Adsorbent and preparation and application thereof

Abstract

An adsorbent for passive NOx adsorption, the adsorbent comprising a small pore zeolite having an eight membered ring and non-noble metal ions introduced into the pore channels of the zeolite. The invention also relates to a tail gas system comprising the adsorbent and a method for preparing the adsorbent.

Description

Technical Field

[0001] The present invention relates to an adsorbent, for example, but not exclusively, an adsorbent comprising small pore zeolite having an eight-membered ring / octacycle framework structure and non-noble metal ions introduced / doped into its pores; and a method for preparing the adsorbent. The present invention also relates to the use of the adsorbent in an exhaust gas system. Background Art

[0002] Nitrogen oxides (NO x ) are one of the most common air pollutants in the world. NO x gas is usually produced after the reaction between nitrogen and oxygen during the fuel combustion process. Although there are technologies such as selective catalytic reduction (SCR) and selective non-catalytic reduction for reducing post-combustion NO x , it should be understood that those technologies have limited efficiency at low operating temperatures (such as below 200 °C). In particular, such a "low temperature range" is inevitable after the engine starts, which is usually referred to as the cold start period of the engine. Therefore, it should be understood that the cold start NO x emissions mainly including nitric oxide (NO) generated from the exhaust gas of a low-temperature diesel engine during the cold start period of the engine will significantly cause NO x pollution.

[0003] Passive nitrogen oxide adsorption (PNA) has been considered as one of the solutions to such problems. Generally, PNA involves placing an adsorbent upstream of the SCR process to capture the NO emitted during the cold start period. Subsequently, the captured NO can be released at an elevated temperature during the engine preheating period, at which time the downstream SCR process can effectively perform NO x reduction.

[0004] Among the developed passive NO x adsorbents, molecular sieves doped with noble metals such as Pd, Pt or compounds derived therefrom (such as Pt / Pd / Al 2 O 3 , Pt / Pd / CeO 2 etc.) have attracted wide attention because it is considered that Pt or Pd cations are effective NO adsorption sites for PNA. However, it should be noted that these adsorbents still exhibit insufficient NO adsorption capacity, where complete removal of NO from the engine exhaust has never been achieved at temperatures below 200 °C x . This defect can be attributed to Pd 2+The loading amount is limited (usually less than 2 wt% for the formation of isolated Pd cations). Although the NO adsorption capacity of Pd-zeolite can be enhanced by further increasing the Pd loading amount, this method will also lead to the aggregation of Pd, resulting in a significant decrease in the NO / Pd ratio and a relatively high adsorbent cost. In addition, the reusability of Pd-zeolite has not been demonstrated by the results of cyclic NO adsorption / desorption within simulated engine exhaust. This is particularly concerning due to the insufficient hydrothermal stability of the previously reported Pd species.

[0005] Accordingly, the present invention seeks to eliminate or at least mitigate such drawbacks by providing novel or otherwise improved adsorbents for PNA, particularly adsorbents containing non-noble metal cations as NO adsorption sites. Summary of the Invention

[0006] In a first aspect of the present invention, there is provided an adsorbent for passive NO x adsorption, which comprises a small-pore zeolite having an eight-membered ring and non-noble metal ions introduced into its pores.

[0007] Optionally, the non-noble metal ions include Na + , K + , Mg 2+ , Ca 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Y 3+ , La 3+ , Ce 3+ , Eu 3+ , Tb 3+ or Yb 3+ and any one of them.

[0008] In an optional embodiment, the non-noble metal ions are selected from the group consisting of Na + , Mg 2+ , Ca 2+ , Co 2+ , Ni 2+ and combinations thereof.

[0009] Optionally, the eight-membered ring of the small-pore zeolite is selected from any one of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, LTA, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON.

[0010] In an optional embodiment, the small-pore zeolite comprises the framework structure of any one of CHA and LTA.

[0011] Optionally, the framework structure of LTA includes an Si / Al ratio of 5.5 to 6.

[0012] Optionally, the small-pore zeolite comprises the framework structure of LTA-6.

[0013] Optionally, the degree of ion exchange of the small-pore zeolite with non-noble metal ions is 20% to 104%.

[0014] Optionally, the small-pore zeolite contains a plurality of exchangeable sites that can be ion-exchanged with non-noble metal ions.

[0015] Optionally, the adsorbent has a particle size of about 0.5 mm.

[0016] Optionally, the non-noble metal ion is Co 2+ and Ni 2+ and the small-pore zeolite has the framework structure of LTA-6.

[0017] Optionally, the small-pore zeolite is introduced with about 5 wt% to about 6 wt% of Ni 2+ .

[0018] Optionally, the small-pore zeolite is introduced with about 2 atomic% to about 3 atomic% of Ni 2+ .

[0019] In an optional embodiment, the small-pore zeolite is introduced with about 5 wt% to about 6 wt% of Co 2+ .

[0020] Optionally, the small-pore zeolite is introduced with about 2 atomic% to about 3 atomic% of Co 2+ .

[0021] Optionally, the adsorbent has a NO adsorption capacity of about 0.22 mmol / g to about 0.35 mmol / g at about 80 °C. In an optional embodiment, the adsorbent (such as Co-LTA-6 and Ni-LTA-6 adsorbents) has a NO adsorption capacity of about 675 μmol / g to about 773 μmol / g at about 100 °C.

[0022] Optionally, the adsorbent is capable of capturing an effective amount of NO at a first temperature or below the first temperature and releasing substantially the same amount of the captured NO at a second temperature above the first temperature.

[0023] Optionally, the first temperature is about 183 °C to about 255 °C.

[0024] Optionally, the second temperature is about 195 °C to about 460 °C.

[0025] Optionally, the effective amount of NO is about 200 ppm.

[0026] In a second aspect of the present invention, there is provided an exhaust gas system for an internal combustion engine, which includes a passive NO x adsorber and an exhaust gas treatment component. The passive NO x adsorber contains the adsorbent according to the first aspect, and the exhaust gas treatment component is configured downstream of the adsorber and in fluid communication with the adsorber.

[0027] In an optional embodiment, the adsorber is loaded with about 0.2 g to about 1.2 g of the adsorbent.

[0028] Optionally, the adsorber loaded with the adsorbent has a bed porosity of about 70% to about 80%.

[0029] Optionally, the adsorbent is thermally pretreated at a temperature of about 300 °C or higher.

[0030] Optionally, the exhaust gas treatment component includes at least one of a selective catalytic reduction (SCR) catalyst, a particulate filter, an SCR filter, a NO x adsorbent catalyst, a three-way catalyst, and an oxidation catalyst.

[0031] In a third aspect of the present invention, there is provided a method for preparing the adsorbent according to the first aspect, which includes the following steps: providing a small-pore zeolite containing NH 4 + ions or Na + ions; and adding the small-pore zeolite to a first solution containing a non-noble metal nitrate or a non-noble metal acetate to carry out an ion exchange reaction, so that NH 4 + ions or Na +The ions are replaced by non-noble metals.

[0032] Optionally, the small pore zeolite contains NH 4 + LTA-6 or Na in ionic form + LTA-6 in ionic form.

[0033] Optionally, NH 4 + The solid / liquid ratio of LTA-6 in ionic form to the first solution is about 1 g / 50 mL.

[0034] Optionally, Na + The solid / liquid ratio of LTA-6 in ionic form to the first solution is about 1 g / 100 mL.

[0035] In an optional embodiment, the non-noble metal includes any one of Na, K, Mg, Ca, Mn, Co, Ni, Cu, Zn, Y, La, Ce, Eu, Tb or Yb. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will now be described more specifically by way of example only with reference to the accompanying drawings, in which:

[0037] Figure 1 A schematic diagram of an experimental apparatus for column breakthrough dynamic adsorption testing is shown;

[0038] Figure 2A XRD patterns of H-, Na-, K-, Mg- and Ca-LTA-6 zeolites are shown;

[0039] Figure 2B XRD patterns of Mn-, Co-, Ni-, Cu- and Zn-LTA-6 zeolites are shown;

[0040] Figure 2C XRD patterns of Y-, La-, Ce-, Eu-, Tb- and Yb-LTA-6 zeolites are shown;

[0041] Figure 2D Synchrotron radiation XRD of Ni-LTA-6 is shown;

[0042] Figure 3 Is a table summarizing the ion exchange degree of LTA-6 zeolite;

[0043] Figure 4A Shows the N of H-, Na-, K-, Mg- and Ca-LTA-6 zeolites at 77 K temperature 2 Adsorption isotherm;

[0044] Figure 4Bshows the N adsorption isotherms of Mn-, Co-, Ni-, Cu-, and Zn-LTA-6 zeolites at 77 K; 2 ;

[0045] Figure 4C shows the N adsorption isotherms of Y-, La-, Ce-, Eu-, Tb-, and Yb-LTA-6 zeolites at 77 K; 2 ;

[0046] Figure 5 is a table summarizing the porous properties of LTA-6 zeolites;

[0047] Figure 6A shows the NO breakthrough curves of H-, Na-, K-, Mg-, and Ca-LTA-6 zeolites (activated at 300 °C) during NO adsorption using NO / N (200 ppm NO balanced by N) at room temperature (about 25 °C); 2 (by N 2 equilibrated 200 ppm NO) during NO adsorption;

[0048] Figure 6B shows the NO breakthrough curves of Mn-, Co-, Ni-, Cu-, and Zn-LTA-6 zeolites (activated at 300 °C) during NO adsorption using NO / N (200 ppm NO balanced by N) at room temperature (about 25 °C); 2 (by N 2 equilibrated 200 ppm NO) during NO adsorption;

[0049] Figure 6C shows the NO breakthrough curves of Y-, La-, Ce-, Eu-, Tb-, and Yb-LTA-6 zeolites (activated at 300 °C) during NO adsorption using NO / N (200 ppm NO balanced by N) at room temperature (about 25 °C); 2 (by N 2 equilibrated 200 ppm NO) during NO adsorption;

[0050] Figure 6D shows the NO breakthrough curves of Na-, Mg-, Ca-, Co-, and Ni-LTA-6 zeolites (activated at 300 °C) during NO adsorption using NO / N (200 ppm NO balanced by N) at 80 °C; 2 (by N 2 equilibrated 200 ppm NO) during NO adsorption;

[0051] Figure 7 is a table summarizing the NO adsorption capacity of LTA-6 zeolites (activated at 300 °C) in NO / N (200 ppm NO balanced by N) at 100 kPa; 2 (200 ppm NO balanced by N 2 equilibrated NO);

[0052] Figure 8AShows NO breakthrough curves of Na-, Mg-, Ca-, Co-, and Ni-LTA-6 zeolites (activated at 300 °C) during NO adsorption using NO / N 2 (balanced with 200 ppm NO by N 2 ) at 100 °C;

[0053] Figure 8B Shows the NO storage capacity and NO / cation ratio of Na-, Mg-, Ca-, Co-, and Ni-LTA-6 zeolites (activated at 300 °C) in NO / N 2 (balanced with 200 ppm NO by N 2 ) at 100 °C and 100 kPa;

[0054] Figure 8C Shows NO breakthrough curves of Na-, Mg-, Ca-, Co-, and Ni-LTA-6 zeolites (activated at 600 °C) during NO adsorption / desorption using programmed heating from 80 to 600 °C at a heating rate of 15 °C / min;

[0055] Figure 8D Shows Ni K-edge XANES spectra of Ni-LTA-6, Ni foil, and NiO;

[0056] Figure 8E Shows the XPS spectra of Ni 2p in LTA-6;

[0057] Figure 8F Shows the Fourier transform of the k 2 weighted EXAFS spectra of Ni-LTA-6, Ni foil, and NiO in R space;

[0058] Figure 8G Is a table comparing the NO capacity and NO / metal (cation) ratio between reported Pd-zeolites and Co-LTA-6 and Ni-LTA-6;

[0059] Figure 9A Shows the relationship between the NO adsorption capacity (adsorption temperature 100 °C, pressure 100 kPa, sample activation temperature 600 °C), DFT binding energy, and charge / size ratio of metal cations. NO adsorption was measured at room temperature and 100 kPa using NO / N 2 (balanced with 200 ppm NO by N 2 ). The NO number per unit cell was used as the normalized unit of capacity to avoid bias caused by different metal cation weights;

[0060] Figure 9B Shows in-situ DRIFTS results of Mg-, Ni-, and Co-LTA-6 during NO adsorption;

[0061] Figure 10A shows the breakthrough curves of NO, CO, and H 2 (by N 2 equilibrated 200 ppm NO) of Ni-LTA-6 (activated at 300 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O;

[0062] Figure 10B shows the breakthrough curves of NO, CO, and H 2 (by N 2 equilibrated 200 ppm NO) of Ni-LTA-6 (first activated at 300 °C and completed the first programmed heating cycle from 80 °C to 600 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O;

[0063] Figure 10C shows the breakthrough curves of NO, CO, and H 2 (by N 2 equilibrated 200 ppm NO) of Ni-LTA-6 (activated at 600 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O;

[0064] Figure 10D shows the breakthrough curves of NO, CO, and H 2 (by N 2 equilibrated 200 ppm NO) of Ni-LTA-6 (first activated at 600 °C, pretreated with N 2 containing 1% H 2 O, and finally activated at 300 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O;

[0065] Figure 10E shows the breakthrough curves of NO, CO, and H 2 (by N 2 equilibrated 200 ppm NO) of Ni-LTA-6 (first activated at 600 °C, pretreated with dry air containing 400 ppm CO 2 , and finally activated at 300 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H2 Penetration curve of O;

[0066] Figure 10F Shows Figures 10A to 10C Comparison of NO penetration curves;

[0067] Figure 11A Shows NO, CO, and H 2 (from N 2 equilibrated 200 ppm NO) of Co-LTA-6 (activated at 300 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O penetration curves;

[0068] Figure 11B Shows for the second cycle NO, CO, and H 2 (from N 2 equilibrated 200 ppm NO) of Co-LTA-6 (first activated at 300 °C and completed the first programmed heating cycle from 80 °C to 600 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O penetration curves;

[0069] Figure 11C Shows NO, CO, and H 2 (from N 2 equilibrated 200 ppm NO) of Co-LTA-6 (activated at 600 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 O penetration curves;

[0070] Figure 11D Shows Figures 11A to 11C Comparison of penetration curves;

[0071] Figure 11E Shows NO, CO, and H 2 (from N 2 equilibrated 200 ppm NO) of Co-LTA-6 (first activated at 600 °C, pretreated with N containing 1% H 2 O, and finally activated at 300 °C) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min; 2 and H 2 and H 2 O penetration curves;

[0072] Figure 11FThe NO / N ratio is shown during the heating process from 80°C to 600°C at a heating rate of 15°C / min. 2 (By N 2 Co-LTA-6 (first activated at 600 °C with 1% H 2 O'N 2 pre-treated, and finally activated at 300°C) 2 and H 2 The penetration curve of O;

[0073] Figure 12A The results show that during the heating process from 80°C to 600°C at a heating rate of 15°C / min, the 2 The balance contains 200ppm NO, 200ppm CO, 50ppm C 3 H 8 , 5% CO 2 , with 10% O 2 (called NO / Mix) or without 10% O 2 (called O-free 2 NO / Mix without O 2 ) of the simulated engine exhaust gas;

[0074] Figure 12B The results show that during the heating process from 80°C to 600°C at a heating rate of 15°C / min, the 2 NO, CO, C in Ni-LTA-6 (activated at 600℃) mixture 3 H 8 , CO 2 and H 2 The penetration curve of O;

[0075] Figure 12C The NO, CO, C and CO of Ni-LTA-6 (activated at 600 °C) in NO / gas mixture during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min are shown. 3 H 8 , CO 2 and H 2 The penetration curve of O;

[0076] Figure 12D The cyclic adsorption / desorption results of Ni-LTA-6 activated / regenerated at 600 °C with dry He purge in NO / gas mixture are shown;

[0077] Figure 12E It shows that in the absence of O 2Cyclic adsorption / desorption results of Ni-LTA-6 activated / regenerated at 600 °C by purging with dry He in NO / mixed gas;

[0078] Figure 13A Shows the breakthrough curves of NO of Ni-LTA-6 activated at 600 °C in simulated engine exhaust gas containing different levels of H 2 O content (0% (i.e., dry), 1% and 2% H 2 O) and consisting of N 2 balanced 200 ppm NO, 200 ppm CO, 50 ppm C 3 H 8 , 5% CO 2 and 10% O 2 (referred to as NO / mixed gas) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min;

[0079] Figure 13B Shows the breakthrough curves of NO of Ni-LTA-6 (1.2 g loading) activated at 600 °C in simulated engine exhaust gas with or without SO 2 pretreatment and consisting of N 2 balanced 200 ppm NO, 200 ppm CO, 50 ppm C 3 H 8 , 5% CO 2 and 10% O 2 (referred to as NO / mixed gas) and 2% H 2 O;

[0080] Figure 14 Shows the breakthrough curves of NO of Ni-LTA-6 (activated at 600 °C, 0.2 g or 1.2 g loading) in simulated engine exhaust gas containing N 2 balanced 200 ppm NO, 200 ppm CO, 50 ppm C 3 H 8 , 5% CO 2 and 10% O 2 (referred to as NO / mixed gas) and containing 2% H 2 O;

[0081] Figure 15 Shows Ni-LTA-6 (in SO 2The cyclic adsorption / desorption results after pre-adsorption and activation at 600 °C. Between every two cycles, Ni-LTA-6 was allowed to cool naturally in the absence of a drying He purge. During the cooling process, the column outlet was connected to ambient air (60 - 70% RH);

[0082] Figure 16 Shows the NO adsorption / desorption breakthrough curves of 1.2 g of Ni-LTA-6 in wet simulated engine exhaust (referred to as NO / mixed gas (2% H 2 O))) during programmed heating from 80 °C to 600 °C at a heating rate of 15 °C / min. The NO / mixed gas contains 200 ppm NO, 200 ppm CO, 50 ppm C x balanced by N 2 , 5% CO 3 H 8 , 10% O 2 and 2% H 2 O. 2

[0083] Figure 17A Shows the synchrotron radiation XRD patterns of Ni-LTA-6 before and after 10 PNA cycles;

[0084] Figure 17B Shows the (Cu target) XRD patterns of Ni-LTA-6 before and after 10 PNA cycles, which are complementary to Figure 17A ;

[0085] Figure 17C Shows the Ni 2p XPS of Ni-LTA-6 before and after 10 PNA cycles corresponding to Figure 17A and Figure 17B ;

[0086] Figure 18A Shows the Ni K-edge XANES spectra of Ni-LTA-6, NiO, and Ni foil before and after 10 PNA cycles; and

[0087] Figure 18B Shows the Fourier transform of the k 2 -weighted EXAFS spectra in the R space of Ni-LTA-6, NiO, and Ni foil after 10 PNA cycles. DETAILED DESCRIPTION

[0088] As used herein, unless the context clearly indicates otherwise, the forms "a" and "the" are intended to include both singular and plural forms.

[0089] ​As used in this invention, the words "example" or "exemplary" are intended to be used as examples, instances, or illustrations. Any aspect or design described as "exemplary" in this disclosure is not necessarily to be construed as more preferred or advantageous than other aspects or designs. Instead, the use of the words "example" or "exemplary" is intended to present concepts in a concrete manner. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless otherwise specified or clear from the context, "X employs A or B" is intended to mean any of the natural inclusive permutations in a natural inclusive arrangement. That is, if X employs A; X employs B; or X employs both A and B, then "X employs A or B" is satisfied in any of the foregoing instances.

[0090] As used herein, the phrase "about" is intended to refer to a value that slightly deviates from the value stated herein. For example, "about 0.5 mm" can mean any value from 0.45…0.48…0.5…0.51…0.55 mm; "about 2 wt%" can mean any value from 1.8…1.85…1.9…2…2.05…2.1…2.2 wt%; "about 0.22 mmol / g" can mean any value from 0.20…0.205…0.21…0.22…0.222…0.225 wt%; "about 80 °C" can mean any value from 78…78.5…79.5…80…80.2…81.2…82 °C; "about 255 °C" can mean any value from 253…254.5…255…255.2…256…256.8…257 °C.

[0091] Molecular sieves, particularly small-pore molecular sieves, or small-pore zeolites, may be attractive candidates for passive NO x adsorption (PNA) because it is believed that the negatively charged Si-O-Al framework of zeolites, along with the restricted pore space and its good structural hydrothermal stability, can allow for a rich distribution of charge-balancing cations as effective adsorption sites. While the above properties of zeolites may be optimal for accommodating Pd cations for PNA, it is believed that the use of noble metal ions will result in various PNA defects as mentioned herein.

[0092] Without being bound by theory, the inventors have designed, through their own research, testing, and experimentation, an adsorbent for PNA, particularly an adsorbent containing non-noble metal ions accommodated by a zeolite framework. In embodiments of the present invention, it has been found that the non-noble metal PNA adsorbent has outstanding NO adsorption / desorption capabilities and reusability in scenarios simulating engine cold start, warm-up, and shutdown, indicating its significant practical application and industrialization potential.

[0093] According to the present invention, there is provided a method for passive NO xThe adsorbed adsorbent. The adsorbent may comprise a molecular sieve, particularly small-pore zeolites having an eight-membered ring / octagonal ring framework structure and non-noble metal ions introduced / doped into their pores. In particular, the introduced non-noble metal ions can serve as NO adsorption sites.

[0094] The term "small-pore zeolite" generally refers to a zeolite having a framework structure with pore entrance dimensions of an eight-ring window, which framework structure has a maximum free pore diameter of about 0.41 nm to about 0.43 nm. It should be understood that this pore diameter can be calculated by subtracting the diameter of the oxygen ion (0.27 nm) in the silicate structure from the interatomic distance between two opposite oxygen atoms across the ring. In an embodiment of the present invention, the eight-membered ring of the small-pore zeolite can be selected from any one of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, LTA, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON.

[0095] In a specific embodiment, the small-pore zeolite may comprise the framework structure of any one of CHA and LTA. In a more specific embodiment, the small-pore zeolite may comprise the framework structure of LTA. Preferably, the framework structure of LTA may have an Si / Al ratio of 5.5 to 6. That is, in this embodiment, the small-pore zeolite includes the framework structure of LTA-6. It is believed that by using LTA zeolite having such an Si / Al ratio, good structural stability and promising low-concentration NO gas capture ability will be provided for the adsorbent of the present invention, as discussed in the later part of this disclosure.

[0096] It should be understood that the zeolite or the framework structure of the zeolite is generally anionic, which is balanced by charge-compensating cations such as H + ions, NH 4 + ions, etc. In particular, these charge-compensating cations can exist as multiple exchangeable sites for ion exchange with non-noble metal ions in the zeolite or its framework structure. That is, multiple exchangeable sites including H + and NH 4 + are replaced / introduced with non-noble metal ions / ion-exchanged with non-noble metal cations. Through such an ion exchange process, the small-pore zeolite thus accommodates non-noble metal ions as NO adsorption sites.

[0097] It should be understood that different non-noble metal ions may have different degrees of ion exchange. In an embodiment of the present invention, the degree of ion exchange of the adsorbent may be from 20% to 104%.

[0098] As used herein, "non-noble metal ions" generally include monovalent, divalent or trivalent cations of alkali metals, alkaline earth metals, transition metals or rare earth metals selected from any one of the following: Na + 、K + 、Mg 2+ 、Ca 2+ 、Mn 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Y 3+ 、La 3+ 、Ce 3+ 、Eu 3+ 、Tb 3+ ,or Yb 3+ 。In a specific embodiment, the non-noble metal ions may be selected from the group consisting of Na + 、Mg 2 + 、Ca 2+ 、Co 2+ 、Ni 2+ and combinations thereof.

[0099] The adsorbent can have various physical forms according to actual needs. In one embodiment, the adsorbent can be configured as particles, which can have a particle size of, for example, about 0.5 mm.

[0100] As a specific embodiment, the adsorbent can comprise small-pore zeolite having a framework structure of LTA-6 (also known as LTA-6 zeolite), into which is introduced either Co 2+ or Ni 2+ . The adsorbent can have a NO adsorption capacity of about 0.22 mmol / g to about 0.35 mmol / g at about 80 °C. In addition, the adsorbent may be able to capture an effective amount of NO, such as 200 ppm of NO, at a first temperature (such as about 183 °C to about 255 °C) or below this first temperature, and release substantially the same amount of the captured NO at a second temperature higher than the first temperature, such as at a second temperature of about 195 °C to about 460 °C.

[0101] In one embodiment where the non-noble metal ion is Co 2+ ,the LTA-6 zeolite can be introduced with about 5 wt% to about 6 wt% of well-dispersed isolated Co 2+ (corresponding to an introduction of 2 atomic% to about 3 atomic% of Co 2+ ). In the case where the non-noble metal ion is Ni2+ In another embodiment, the LTA-6 zeolite may be introduced with about 5 wt% to about 6 wt% of well-dispersed and independent Ni 2+ (introducing corresponding to 2 atomic % to about 3 atomic % of Ni 2+ ). This loading amount is much higher than that of the currently reported noble metal PNA adsorbents (less than 2 wt%, 0.4 atomic %), enabling the zeolite to have a larger number of NO adsorption sites, thus having a strong NO adsorption capacity. In an exemplary embodiment, LTA-6 may be introduced with about 5 wt% to about 6 wt% of Ni 2+ , and it is found that this adsorbent can completely capture NO (200 ppm) in the temperature range of 80 - 255 °C from wet engine exhaust gas, and then desorb the captured NO in the temperature range of 260 - 420 °C. Details of the performance will be discussed in the later part of this disclosure.

[0102] Now a method for preparing the adsorbent will be described. The method may include the following steps: providing a small-pore zeolite containing NH 4 + ions or Na + ions; and adding the small-pore zeolite to a first solution containing a non-noble metal nitrate or a non-noble metal acetate for an ion exchange reaction, such that the NH 4 + ions or Na + ions are replaced by non-noble metals.

[0103] In one embodiment, the small-pore zeolite may comprise LTA-6 in the form of NH 4 + ions or LTA-6 in the form of Na + ions. Specifically, LTA-6 in the form of NH 4 + ions or LTA-6 in the form of Na + ions can be prepared by hydrothermal synthesis of LTA-6, followed by an ion exchange reaction with ammonium nitrate and / or sodium nitrate.

[0104] In an exemplary embodiment, LTA-6 can be prepared by stirring a mixture containing aluminum sec-butoxide, Ludox HS-40 colloidal silica, 25% solution of tetraethylammonium hydroxide (TEAOH), 20% solution of diethyldimethylammonium hydroxide (DEDMAOH), sodium chloride (NaCl), and tetramethylammonium chloride (TMACl) in a Teflon liner of a stainless-steel autoclave at room temperature for 24 hours. Subsequently, the mixture is sealed in a stainless-steel autoclave and aged for a duration of 13 days in an air convection oven at 98 °C, and then aged for a duration of 7 days at 125 °C. Thereafter, the LTA zeolite can be separated from the supernatant by filtration or centrifugation, and then washed several times with deionized water, such as 5 times. Then, the as-synthesized LTA zeolite can be dried in a vacuum oven at 60 °C for at least 8 hours. Finally, LTA-6 can be calcined at 600 °C for 10 hours at a heating rate of 2 °C / min to remove the organic structure-directing agent (OSDA). Then the LTA-6 zeolite can be ion-exchanged in a 1 M ammonium nitrate solution to obtain LTA-6 in the NH 4 + ion form.

[0105] Specifically, the ion exchange of NH 4 + can be carried out at a solid / liquid ratio of 1 g / 50 mL and magnetically stirred at 60 °C for a duration of 24 hours. Thereafter, the LTA zeolite is separated by filtration or centrifugation and washed several times with deionized water. Finally, the washed LTA zeolite can be dried in an air convection oven at 60 °C. These procedures can be repeated four times to complete the NH 4 + exchange process.

[0106] In one embodiment, LTA-6 in the Na + ion form can be obtained by ion-exchanging with LTA-6 in the NH 4 + ion form in a 1 M sodium nitrate solution. Specifically, the ion exchange of Na + can be carried out by using LTA in the NH 4 + ion form in a 1 M sodium nitrate solution at a solid / liquid ratio of 1 g / 50 mL and magnetically stirred at 60 °C for a duration of 24 hours. Thereafter, the LTA zeolite in the Na + ion form can be separated by filtration or centrifugation and washed several times with deionized water. Finally, the washed LTA zeolite can be dried in an air convection oven at 60 °C. These procedures can be repeated four times to complete the Na + exchange process.

[0107] The non-noble metals in the first solution may include any one of Na, K, Mg, Ca, Mn, Co, Ni, Cu, Zn, Y, La, Ce, Eu, Tb, or Yb. In the embodiments respectively related to Na + , K + , Mg 2+ and Ca 2+ , for the ion exchange reaction, LTA-6 in the form of NH 4 + ions may be added to the first solution containing 1 M metal nitrate (Na / K / Mg / Ca nitrate) at a solid / liquid ratio of 1 g / 50 mL and magnetically stirred at room temperature (about 25 °C) for a duration of 24 hours. In the embodiments respectively related to the transition metal cations Mn 2 + , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Y 3+ , La 3+ , Ce 3+ , Eu 3+ , Tb 3+ or Yb 3+ ), in another embodiment of the ion exchange, LTA-6 in the form of Na + ions may be added to the first solution containing 1 M metal nitrate or metal acetate (Mn / Co / Ni / Cu / Zn / Y / La / Ce / Eu / Tb / Yb nitrate or acetate) at a solid / liquid ratio of 1 g / 100 mL and magnetically stirred at room temperature (about 25 °C) for a duration of 24 hours.

[0108] After that, the LTA zeolite in the non-noble metal ion-exchanged form may be separated by filtration and washed several times with deionized water. Finally, the washed LTA zeolite may be dried in an air convection oven at 60 °C. These procedures may be repeated four times to complete the exchange process.

[0109] Another aspect of the present invention relates to a simulated exhaust gas system for an internal combustion engine, which includes a passive NO x adsorber and an exhaust gas treatment component. The passive NO x adsorber contains the adsorbent as described herein, and the exhaust gas treatment component is configured downstream of the adsorber and in fluid communication with the adsorber.

[0110] In one embodiment, the exhaust gas treatment component may include a selective catalytic reduction (SCR) catalyst, a particulate filter, an SCR filter, NO xAt least one of an adsorbent catalyst, a three-way catalyst, and an oxidation catalyst. It should be understood that these components are well-known in the art and suitable treatment components can be selected according to actual needs.

[0111] The exhaust gas system can be configured such that passive NO x The adsorber is positioned close to the engine, and the exhaust gas treatment component is located downstream relative to the adsorber and in fluid communication with the adsorber. It should be understood that by configuring the exhaust gas system in this way, it will be ensured that the exhaust gas of the engine first flows through the adsorber for PNA before contacting the exhaust gas treatment component, thereby minimizing the low-temperature exhaust gas during the cold start period of the engine.

[0112] Passive NO x The adsorber can have any shape and / or size suitable for actual needs. In one embodiment, passive NO x The adsorber can be a column loaded with an adsorbent, particularly an adsorbent that has been thermally pretreated at about 300 °C or above, such as up to about 600 °C. It is believed that by thermally pretreating the adsorbent at different temperatures, it is possible to manipulate the NO adsorption / desorption window of the adsorbent, thereby enabling more effective NO capture during the cold start period.

[0113] The adsorber can be loaded with about 0.2 g to about 1.2 g of the adsorbent and have a bed porosity of about 70% to about 80%. In a specific embodiment where the adsorber is loaded with about 1.3 g of the adsorbent, it was unexpectedly found that such a loading amount can promote the adsorption of water from the wet engine exhaust gas without affecting the PNA performance of the adsorbent / adsorber. Details of the effects of the pretreatment temperature and the adsorbent loading amount will be disclosed in a later part of this disclosure.

[0114] In the following, the present invention will be described more specifically by way of examples, but the present invention is not limited thereto.

[0115] Examples

[0116] Preparation of LTA zeolite

[0117] LTA zeolite with a Si / Al ratio of 6 (abbreviated as LTA-6) was synthesized by the following steps: 11.78 g of a 25% solution of tetraethylammonium hydroxide (TEAOH), 7.95 g of a 20% solution of diethyldimethylammonium hydroxide (DEDMAOH), 1.64 g of aluminum sec-butoxide, and 10 g of Ludox HS-40 colloidal silica were successively mixed in the polytetrafluoroethylene liner of a stainless steel autoclave. Vigorous stirring was required after adding each substance. Then, 5 g of H was evaporated from the mixture 2O. The obtained mixture was sealed in a stainless - steel autoclave and aged in an air - convection oven at 95 °C for 1 day. After the mixture was cooled to room temperature, a solution containing 0.2 g of sodium chloride (NaCl), 0.37 g of tetramethylammonium chloride (TMACl) and 5 g of H 2 O was added dropwise under vigorous stirring. Then the mixture was magnetically stirred at room temperature for a duration of 24 hours. Finally, the mixture was sealed in a stainless - steel autoclave and aged in an air - convection oven at 98 °C for a duration of 13 days, and then aged at 125 °C for a duration of 7 days. After hydrothermal synthesis, the LTA zeolite was separated from the supernatant and then washed 5 times with deionized water by centrifugation. Then, the as - synthesized LTA zeolite was dried overnight in a vacuum oven at 60 °C. Finally, LTA - 6 was calcined at 600 °C at a heating rate of 2 °C / min to remove the OSDA. This calcination was carried out in a continuous gas flow (compressed air, Linde plc. HK) at a flow rate of 50 mL / min for a duration of 10 hours.

[0118] First, the as - synthesized LTA - 6 was ion - exchanged in 1 M ammonium nitrate (NH 4 NO 3 ) solution to obtain LTA in the NH 4 + ionic form. The NH 4 + ion - exchange was carried out at a solid / liquid ratio of 1 g / 50 mL and magnetically stirred at 60 °C for a duration of 24 hours. Then, the LTA zeolite was separated by filtration and washed several times with deionized water. Finally, the washed LTA zeolite was dried in an air - convection oven at 60 °C. These procedures were repeated four times to complete the NH 4 + exchange process. The LTA zeolite in proton (H + ) form was prepared by calcining the NH 4 + form of LTA at 550 °C at a heating rate of 2 °C / min. This calcination was carried out in a continuous gas flow (compressed air, Linde plc. HK) at a flow rate of 50 mL / min for a duration of 10 hours. The ion - exchanges of Na + , K + , Mg 2 + and Ca 2+ were carried out respectively by using the NH 4 + form of LTA in 1 M metal nitrate solutions at a solid / liquid ratio of 1 g / 50 mL according to the procedures mentioned above. All transition - metal cations (including Mn 2+ , Co 2+ , Ni2+ , Cu 2+ , Zn 2+ , Y 3+ , La 3+ , Ce 3+ , Eu 3+ , Tb 3+ and Yb 3+ ) The ion exchange of (is carried out respectively by using LTA in the form of Na + ions in a 0.05 M metal acetate / nitrate solution at a solid / liquid ratio of 1 g / 100 mL according to the procedure mentioned above at room temperature. The LTA zeolite exchanged with metal cations and the LTA zeolite in the form of protons (H + ) are named M-LTA-6, where M represents the type of charge-balancing cation.

[0119] Methods and Characterization

[0120] Structural Characterization

[0121] X-ray powder diffraction (XRD) was performed using an X’Pert3 Powder, PANalytical to evaluate the crystallinity and phase purity of the zeolite adsorbent. The X’Pert3 Powder, PANalytical is equipped with a Cu anode (λ = 0.15406 nm) and runs in the 2θ range from 5° to 50° at a step of 0.026° under a voltage of 40 V and a current of 40 mA. X-ray energy dispersive spectroscopy (EDS) was measured using an Oxford Aztec Energy X-MAX 50 attached to a scanning electron microscope (FEI Quanta 450FEG) to determine the elemental composition of the zeolite adsorbent. To improve the accuracy, the elemental composition was calculated from the average values of multiple spots from multiple coatings. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed on an Agilent 720ES with a concentric pneumatic nebulizer to reconfirm the degree of ion exchange of the zeolite adsorbent. Nitrogen (N 2 ) adsorption isotherms were measured at -196.15 °C using a Micromeritics 3Flex to obtain the porous properties of the adsorbent. Specifically, the Brunauer-Emmett-Teller (BET) surface area was calculated by the BET theory. The micropore surface area, external surface area, and micropore volume were calculated by the t-plot method. Before the adsorption measurement, the adsorbent was activated at 300 °C under high vacuum (10 -6 Pa) for 10 hours to remove pre-adsorbed impurities. Using a wavelength of The Mythen-II detector collected synchrotron radiation XRD data at the PD beamline at the Australian Synchrotron, ANSTO. Synchrotron radiation X-ray absorption spectroscopy (XAS) was performed at the XAS beamline at the Australian Synchrotron, ANSTO. XAS spectra were recorded at the nickel K absorption edge in transmission mode. X-ray photoelectron spectroscopy (XPS) spectra were recorded using an XPS spectrometer (Thermo Scientific K-Alpha+, USA). Using a Thermo Nicolet i550 spectrometer with a scanning rate of 64 times and a resolution of 4 cm -1 in the 200 ppm NO balanced by N 2 (referred to as NO / N 2 ), in-situ DRIFTS spectra during the NO 2 adsorption process were collected. Before the adsorption measurement, the adsorbent was activated in an Ar flow of 40 mL / min at 400 °C for 3 hours to remove pre-adsorbed impurities.

[0122] NO Adsorption / Desorption Experiments

[0123] The NO adsorption / desorption ( Figure 1 ) was measured by using an in-house constructed column breakthrough dynamic adsorption device. In this experimental setup, a stainless-steel column with an inner diameter of 0.4 cm and a length of 10 cm was used to hold the adsorbent. The column was properly placed in a furnace (Carbolite) and interconnected with the inlet and outlet piping systems. The flow rate of the feed gas was precisely controlled by a digital mass flow controller (Alicat Scientific, USA). The concentrations of NO x and accompanying gas components at the outlet were detected by a gas analyzer. Before the NO adsorption / desorption test, the column was loaded with 0.2 g or 1.2 g of adsorbent, respectively. The size of the adsorbent particles was approximately 0.5 mm, and the bed porosity was estimated to be in the range of 70% to 80%. The remaining part of the column was filled with glass beads. Subsequently, the adsorbent was subjected to activation in a continuous He flow at a flow rate of 40 mL / min. The activation process was carried out at 300 °C or 600 °C at a heating rate of 2 °C / min and for a duration of 10 hours.

[0124] After the adsorbent activation, the NO adsorption test was carried out at room temperature. The feed gas (referred to as NO / N 2 ) was prepared by mixing 1000 ppm NO (balanced by helium) with a flow rate of 40 mL / min and N 2) with a total flow rate of 200 mL / min and a NO concentration of 200 ppm. The NO concentration at the outlet was detected by an FTIR gas analyzer (MKS MultiGas 6030).

[0125] The NO adsorption capacity was calculated by the following equation.

[0126]

[0127] Where N NO represents the NO adsorption capacity (in mmol / g), Q represents the total flow rate of the feed gas equivalent to 200 mL / min, w is the weight of the activated sample (in g), C represents the NO concentration in the feed gas (200 ppm), C d is the NO concentration detected at the outlet at time t, and Ts is the saturation time (the time when C d changes from 0 to 200 ppm) (in minutes).

[0128] After the adsorbent was activated at 300 °C or 600 °C, the NO adsorption / desorption test was carried out using NO / N 2 during the programmed heating. After the adsorbent was activated, the temperature of the adsorption column was initially maintained at 80 °C. After introducing NO / N 2 feed, the temperature of the adsorption column was gradually increased to 600 °C at a heating rate of 15 °C / min. The adsorption or desorption of NO was defined by comparing the NO concentration at the outlet with the initial 200 ppm concentration in the feed gas.

[0129] After the adsorbent was activated at 600 °C, the NO adsorption / desorption test was carried out using simulated engine exhaust gas (400 ppm NO, 400 ppm CO, 100 ppm C 3 H 8 and 10% CO 2 (balanced by N 2 ). After introducing the simulated engine exhaust gas, the temperature of the adsorption column was increased from 80 °C to 600 °C at a heating rate of 15 °C / min. The feed gas was prepared by mixing the simulated engine exhaust gas with a flow rate of 100 mL / min and a balance gas (air or N 2 ) with a flow rate of 100 mL / min, and its total flow rate was 200 mL / min. The simulated engine exhaust gas without O 2 was named NO / Mix without O 2 (NO / Mix without O 2 ), and the case containing O 2 was named NO / Mix (NO / Mix) 。

[0130] For the tests using wet tail gas, the balance gas (air) of NO / mixed gas was bubbled through a water storage tank at room temperature (about 25 °C) or 40 °C, thereby generating feed gases containing 1% and 2% H 2 O, respectively. For the tests after SO 2 pretreatment, the adsorbent activated at 600 °C was exposed to wet SO 2 feed gas for 10 hours. The feed gas was prepared by mixing 200 ppm SO 2 (balanced by nitrogen) with a flow rate of 100 mL / min and wet air with a flow rate of 100 mL / min, and the total flow rate was 200 mL / min. The concentrations of SO 2 and H 2 O were 100 ppm and 2%, respectively. After SO 2 pretreatment, the adsorbent was reactivated at 600 °C for NO adsorption / desorption tests.

[0131] The cyclic NO adsorption / desorption using NO / mixed gas was carried out by regenerating the adsorbent in a continuous Ar flow at a flow rate of 40 mL / min at 600 °C for 1 hour. Subsequently, the adsorbent was cooled to 80 °C in the Ar flow before starting the next cycle. To further illustrate the reusability of our adsorbent under actual conditions, we simulated scenarios similar to cold start and shutdown of automobiles. Specifically, after the initial cycle of NO adsorption / desorption in the simulated wet tail gas containing 2% H 2 O, the supply of the feed gas was stopped. At the same time, the adsorbent was naturally cooled to 80 °C without undergoing dry Ar exchange, where the adsorption column was exposed to ambient air. Once the adsorbent was cooled to 80 °C, the subsequent cycle was started.

[0132] Example 1

[0133] Characterization of the adsorbent

[0134] The LTA structure, Si / Al ratio, degree of ion exchange, and porous properties of LTA-6 zeolite were characterized by XRD, EDS, ICP-OES, and N 2 adsorption at 77K.

[0135] The XRD pattern of LTA-6 zeolite was consistent with the reported characteristics of LTA zeolite ( Figures 2A to 2D ), thus confirming their high crystallinity and phase purity. The Si / Al ratio and degree of ion exchange were determined by EDS and ICP-OES analyses to provide the elemental composition ( Figure 3 ). The actual Si / Al ratio of LTA-6 was determined to be 5.5.

[0136] The degree of ion exchange is illustrated in Figure 3indicates that alkali metal cations (Na + and K + ), alkaline earth metal cations (Mg 2+ and Ca 2+ ) and divalent transition metal cations (Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ) have a relatively high degree of ion exchange (exceeding 60%). However, due to the steric hindrance caused by the large size of hydrated rare earth metal cations and the limited diffusion kinetics, the trivalent transition metals classified as rare earth metals (Y 3+ , La 3+ , Eu 3+ , Ce 3+ , Tb 3+ and Yb 3+ ) exhibit a relatively low degree of ion exchange (less than 40%). Among these rare earth metal cation-exchanged LTA-6 zeolites, monovalent Na + still seems to be the main cation. It is worth noting that Cu 2+ in LTA-6 shows an over-exchange with a degree of ion exchange higher than 100%, which is due to the overestimation of Cu 2+ caused by the presence of both Cu + and (Cu-O-Cu) 2+ in Cu-LTA.

[0137] The microporous characteristics of LTA-6 zeolite are determined by the N 2 adsorption isotherm at 77 K, as reflected in their type I isotherms ( Figures 4A to 4C ). The surface area and pore volume are calculated based on the N 2 adsorption results at 77 K, where LTA-6 zeolites exhibit similar values ( Figure 5 ). K-LTA is an exception, which shows a negligibly small surface area and pore volume, attributed to the blocking of the probe molecule N + by large K 2 cations. Additionally, slightly smaller surface areas and pore volumes are observed in LTA zeolites exchanged with divalent and trivalent transition metal cations, mainly due to the higher molecular weights of the heavier transition metals compared to alkali metals and alkaline earth metals.

[0138] Example 2

[0139] NO Adsorption Capacity of Metal Cation-Exchanged LTA Zeolites

[0140] To evaluate the potential of non-noble metal cation-exchanged LTA-6 for PNA, NO adsorption tests were conducted at two different temperatures: 25 °C (room temperature) and 80 °C (initial temperature during cold start-up period), where a column breakthrough adsorption configuration was adopted, using a 200 ppm NO gas mixture balanced with N 2 (denoted as NO / N 2 ) and 0.2 g loading of non-noble metal cation-exchanged LTA-6. Among the cations studied, Na + , Ca 2+ , Mg 2+ , Co 2+ , and Ni 2+ were selected as representatives of monovalent and divalent cations for further discussion. After evaluating the NO adsorption capacity calculated at room temperature, the reference adsorbent H-LTA-6 showed negligible NO adsorption capacity ( Figures 6A to 6D and Figure 7 ). Similarly, Na + -exchanged LTA-6 also exhibited negligible NO capacity. In contrast, divalent and trivalent metal cation-exchanged LTA-6 showed significant NO adsorption. This observation indicates that divalent metal cations are effective NO adsorption sites, which is further demonstrated by the DFT binding energy to be discussed later.

[0141] As mentioned, it should be understood that the cold start-up period of the engine will last at least until the engine temperature reaches 200 °C. That is, it is expected that an effective adsorbent for PNA will be able to adsorb NO at least at any temperature below 200 °C. Therefore, NO adsorption tests were further conducted at 100 °C on LTA-6 using monovalent and divalent cation representatives (i.e., Na + , Ca 2+ , Mg 2+ , Co 2+ , and Ni 2+ ). As shown in Figure 8A and 8B , similarly, divalent Ca 2+ , Mg 2+ , Co 2+ , and Ni 2+ -exchanged LTA-6 showed significant NO adsorption. In addition, Ni-LTA-6 showed the highest NO capacity and NO / cation ratio among the zeolites studied, indicating that Ni is the most effective NO adsorption site.

[0142] Given that PNA requires the adsorbent to be able to adsorb NO between 80 - 200 °C and then desorb within 250 - 450 °C after rapid heating, the temperature range of NO adsorption and desorption of divalent non-noble metal cation-exchanged LTA-6 in this work was studied. AsFigure 8C As shown, Ni-LTA-6 is superior to other zeolites due to its highest NO adsorption breakthrough temperature. This finding confirms that Ni sites have superior NO adsorption capacity compared to other divalent metal cations. Notably, Ni-LTA-6 not only achieves complete NO adsorption between 80 - 235 °C, but also promotes complete NO desorption within 250 - 450 °C. This result highlights the appropriate adsorption strength of Ni sites towards NO, which meets the prerequisite of PNA.

[0143] The following characterizations further confirm the divalent cation nature of well-dispersed Ni within Ni-LTA-6. Specifically, the K-edge X-ray absorption near-edge structure (XANES) analysis of Ni shows that the absorption edge between Ni-LTA-6 and NiO is consistent ( Figure 8D ), indicating that Ni is in the +2 oxidation state within Ni-LTA-6. Similar results are also confirmed by analyzing Ni 2p using X-ray photoelectron spectroscopy (XPS) ( Figure 8E ). In addition, the results obtained from the extended X-ray absorption fine structure (EXAFS) analysis in the R space reveal the good dispersion of isolated Ni 2+ within the Ni-LTA-6 framework ( Figure 8F ), as evidenced by the absence of obvious Ni-Ni bonds and the predominance of Ni-O (zeolite framework O) bonds.

[0144] Using the NO / metal (cation) ratio as the normalization standard, the efficiency of Ni 2+ as a NO adsorption site is compared with that of Pd sites. Notably, Ni-LTA-6 exhibits a NO / Ni ratio of 0.89 at 100 °C ( Figure 8B ), exceeding most reported Pd zeolites (NO / Pd ratios below 0.7) and being quite close to the highest reported NO / Pd ratio (between 0.09 - 1) at the same temperature ( Figure 8G ). This result indicates that Ni 2+ is an effective NO adsorption site within LTA-6. More importantly, Ni-LTA-6 exhibits a remarkable NO capacity of 773 μmol / g at 100 °C ( Figure 8B ), which is more than twice the NO capacity of Pd zeolites (usually below 200 μmol / g) reported at the same temperature. This superior NO capacity of Ni-LTA-6 is attributed to the fact that the achievable loading ratio of well-dispersed isolated Ni 2+ (about 5 wt%, 2 at% of Ni-LTA-6) is higher than that of Pd species (usually below 2 wt%, 0.4 at% of Pd zeolites) as effective NO adsorption sites. Therefore, compared to Pd species, Ni2+ It can be considered a more superior NO adsorption site because it has a comparable NO adsorption capacity, is easy to incorporate, and has a significantly reduced cost.

[0145] Example 3

[0146] NO adsorption mechanism

[0147] The DFT binding energy with NO was calculated to evaluate the adsorption strength of LTA zeolite exchanged with non-noble metal cations for NO. As Figure 9A shown, the Na + , Ca 2+ , and Mg 2+ -exchanged LTA-6 showed an increase in the DFT binding energy with NO, which corresponded to an increase in the cation charge-size ratio. This observation indicates that NO adsorption within these adsorbents is controlled by the electrostatic interaction between NO and non-noble metal cations. Notably, Mg 2+ , Co 2+ , and Ni 2+ have similar charge-size ratios, which would generally result in similar electrostatic forces during NO adsorption. Nevertheless, Co-LTA-6 and Ni-LTA-6 showed significantly higher binding energies with NO than Mg-LTA-6 ( Figure 9A ), indicating that the adsorption of NO at Co 2+ and Ni 2+ sites is controlled by different driving forces. In addition, it is worth noting that at temperatures above 110 °C, the electrostatic interaction was proven ineffective for NO adsorption, as demonstrated by the NO breakthrough of Ca-LTA-6 and Mg-LTA-6 around 110 °C ( Figure 8C ). Therefore, the superior NO adsorption capacity of Co-LTA-6 and Ni-LTA-6 at temperatures above 110 °C ( Figure 8C ), which is crucial for practical PNA, is attributed to interactions other than electrostatic forces.

[0148] Meanwhile, at room temperature, Ca-LTA-6 has a higher NO capacity than Mg 2+ , Co 2+ , and Ni 2+ , which is attributed to Ca 2+ "having an appropriate" charge-size ratio, while Mg 2+ , Co 2+ , and Ni 2+ with an overly large charge-size ratio are subject to a more significant "shielding effect". Specifically, Mg 2+ , Co 2+ , and Ni 2+ sites seem to be more susceptible to pre-adsorbed contaminants (such as H2 O and a small amount of chemisorbed CO 2 ) effects. Therefore, via Mg 2+ , Co 2+ and Ni 2+ The available NO capacity of exchanged LTA-6 is limited.

[0149] To further explore the adsorption mechanism of NO on Co 2+ and Ni 2+ sites, in situ DRIFTS tests during NO adsorption were carried out in Mg 2+ , Co 2+ and Ni 2+ exchanged LTA-6. Figure 9B The results plotted in show NO adsorbed in the form of mononitrosyl at the Mg 2+ and Ni 2+ sites. Notably, the red shift of the N-O stretch from 1933 cm -1 (in Mg-LTA-6) to 1893 cm -1 (in Ni-LTA-6) demonstrates the back-bonding interaction between the d orbitals of Ni 2+ and the π* orbitals of NO. This finding reveals that the (π-) back-bonding interaction is the main driving force for the superior NO adsorption ability of Ni-LTA-6. In contrast, the main NO species adsorbed in Co-LTA-6 was found to be dinitrosyl, as evidenced by the doublet bands at 1900 cm -1 and 1811 cm -1 . The superior NO adsorption ability of Ni-LTA-6 compared to Co-LTA-6 may be attributed to the stronger binding energy of mononitrosyl than dinitrosyl.

[0150] Example 4

[0151] Operating temperature ranges for NO adsorption / desorption on Ni-LTA-6 and Co-LTA-6 during programmed heating

[0152] To evaluate the NO adsorption / desorption performance of Ni-LTA-6 and Co-LTA-6 under PNA operating conditions, a series of column breakthrough adsorption / desorption experiments were carried out using 0.2 g loadings of Ni-LTA-6 and Co-LTA-6, with NO / N 2 at a heating rate of 15 °C / min from 80 °C to 600 °C.

[0153] As Figure 10A depicted, NO / N 2200 ppm of NO in the medium can be completely captured by Ni-LTA-6 activated at 300 °C in the temperature range of 80 - 183 °C. The breakthrough of NO occurs above 183 °C, and the subsequent desorption occurs in the temperature range of 195 - 285 °C. It is noteworthy that after the desorption of NO, the NO concentration in the tail gas drops below 200 ppm at temperatures above 300 °C. At the same time, the desorption of H 2 O and CO 2 is observed in the same temperature range ( Figure 10A ). It is believed that these desorbed H 2 O and CO 2 substances are those that were strongly pre-adsorbed from ambient air on the adsorbent during storage and do not seem to desorb completely after activation at 300 °C. Therefore, a small fraction of the Ni 2+ cations that act as strong NO adsorption sites in LTA-6 activated at 300 °C are occupied by these strongly adsorbed pollutants. Thus, when these pollutants desorb at temperatures above 300 °C, the newly released Ni 2+ sites capture additional NO molecules, resulting in the NO concentration dropping below 200 ppm.

[0154] These inferences seem to be supported by the NO adsorption / desorption behavior of Ni-LTA-6 activated at 300 °C during the second cycle (previously heated to 600 °C in the first cycle) and the NO adsorption / desorption behavior of Ni-LTA-6 activated at 600 °C ( Figure 10B and 10C ), where the strongly adsorbed H 2 O and CO 2 are removed by activation / regeneration at 600 °C. Specifically, in both cases, at temperatures above the NO desorption temperature, the NO concentration always remains around the initial concentration of 200 ppm, indicating the absence of NO adsorption.

[0155] In addition, the strongly adsorbed substances occupying the strong Ni 2+ sites are shown to be chemisorbed carbonates co-adsorbed from wet air by CO 2 and H 2 O, respectively. This is demonstrated by control experiments of Ni-LTA-6 activated at 300 °C (which is achieved by activating Ni-LTA-6 at 600 °C, pretreating with wet N 2 or dry air respectively, and finally activating at 300 °C) that retain either H 2 O or CO 2 . In neither case was NO adsorption observed at temperatures above the NO desorption temperature ( Figure 10D and 10E ).

[0156] It should be noted that after increasing the activation / regeneration temperature from 300 °C to 600 °C, the temperature window for NO adsorption / desorption in Ni-LTA-6 increased ( Figure 10F ). Specifically, the temperature at which NO breakthrough occurred increased from 183 °C (activated at 300 °C, Figure 10A ) to 210 - 220 °C (activated at 600 °C, Figure 10B and 10C ). Additionally, the temperature for NO desorption also increased from 195 - 285 °C (activated at 300 °C, Figure 10A ) to 230 - 475 °C (activated at 600 °C, Figure 10B and 10C ). Co-LTA-6 exhibited a similar trend ( Figures 11A to 11F ). This increase in the temperature for NO adsorption / desorption of Ni-LTA-6 activated at 600 °C compared to 300 °C is attributed to the presence of more active Ni 2+ sites for NO capture obtained by removing strongly adsorbed contaminants. It is believed that the elevated temperature window for NO adsorption / desorption provides a significant advantage for the LTA adsorbent in this work for PNA, as it enables more efficient capture of NO during the cold start period. Subsequently, when the downstream NO x reduction process reaches higher efficacy, the captured NO can be released at higher temperatures. In this work, it is noteworthy that Ni-LTA-6 activated at 600 °C can completely capture 200 ppm of NO at temperatures below 200 °C and release most of the captured NO within 250 - 450 °C, which can be considered a potentially effective adsorbent for PNA.

[0157] Example 5

[0158] Ni-LTA-6 for PNA against simulated engine exhaust

[0159] It should be understood that the exhaust emissions from automobiles cover various components other than NO, namely carbon monoxide (CO), carbon dioxide (CO 2 ), hydrocarbons (C x H y ), oxygen (O 2 ), and N 2 . To demonstrate the efficacy of Ni-LTA-6 in an actual scenario, by using a mixture containing 200 ppm NO, 200 ppm CO, 50 ppm C 2 balanced with N 3 H 8 , 5% CO 2 and 10% O 2A series of gas adsorption / desorption experiments were carried out on the simulated engine exhaust gas (denoted as NO / mixed gas). To examine the role of O in the engine exhaust gas, a simulated engine exhaust gas without O 2 was used to conduct parallel gas adsorption / desorption tests to study its effect on PNA. 2 The simulated engine exhaust gas without O 2 (named NO / mixed gas without O

[0160] ) was used to identify potential gas-phase reactions in the simulated engine exhaust gas during programmed heating from 80 °C to 600 °C. Blank experiments without adding a PNA adsorbent were carried out using both NO / mixed gas and NO / mixed gas without O 2 (as depicted). As the NO / mixed gas without O Figure 12A was heated, the CO concentration decreased above 200 °C, which was attributed to the oxidation of CO by trace levels of O 2 in the NO / mixed gas without O 2 at elevated temperatures. Notably, the NO concentration remained largely unchanged before 400 °C because even under high-temperature conditions, the trace O 2 in the NO / mixed gas without O 2 was not sufficient to oxidize NO. For the blank experiment using NO / mixed gas, the presence of 10% O 2 in the feed gas led to more significant CO oxidation. Additionally, a small portion of NO was oxidized to NO 2 at temperatures above 400 °C. The decrease in the C 2 concentration above 400 °C could be attributed to the combustion reaction between C 3 H 8 and O 3 H 8 and O 2 . Note that within the operating temperature range of PNA (from 80 °C to 200 °C), the gas concentrations in both the NO / mixed gas without O 2 and the NO / mixed gas remained consistent, indicating the absence of gas-phase reactions. This observation reveals the effectiveness of using NO / mixed gas and NO / mixed gas without O 2 in this study to demonstrate the PNA performance of the LTA adsorbent in this work.

[0161] Column breakthrough adsorption / desorption tests carried out on Ni-LTA-6 (0.2 g loading) activated at 600 °C clearly showed that under PNA conditions, the presence of CO, CO 2 and C 3 H 8 had no adverse effect on the adsorption / desorption of NO ([[]] Figure 12B and 12C ). Trace amounts of CO, CO 2and C 3 H 8 The instantaneous adsorption of and desorbs at temperatures below 200 °C before NO breakthrough. This observation indicates that the adsorption affinity of NO on Ni-LTA-6 is superior to that of CO, CO 2 and C 3 H 8 .

[0162] As Figure 12B depicted, Ni-LTA-6 activated at 600 °C can prevent NO breakthrough at temperatures below 247 °C, followed by desorption in the temperature range of 275 - 373 °C. Parallel experiments conducted with a NO / mixed gas showed similar results, where NO breakthrough occurred above 260 °C and subsequent desorption occurred between 290 °C and 420 °C. It is important to recognize that a small fraction of NO in the NO / mixed gas undergoes oxidation by O 2 and is subsequently desorbed as NO 2 . In addition, at temperatures above 450 °C under NO / mixed gas conditions without O 2 , a decrease in the NO concentration to below 200 ppm was observed, along with a decrease in the C 3 H 8 concentration. This phenomenon can be attributed to the selective catalytic reduction (SCR) of NO promoted by Ni-LTA-6, where C 3 H 8 is used as a reducing agent. In contrast, this behavior does not exist in the case of the NO / mixed gas due to the depletion of C 3 H 8 via combustion reactions ( Figure 12B ).

[0163] The adsorption / desorption cycles indicate that Ni-LTA-6 exhibits excellent reusability in both the NO / mixed gas and the NO / mixed gas without O 2 , where Ni-LTA-6 is regenerated by He purge at 600 °C ( Figure 12D and 12E ). Ni-LTA-6 has excellent NO adsorption / desorption and regeneration capabilities in simulated engine exhaust and has been considered a promising adsorbent for PNA.

[0164] Example 6

[0165] H 2 O and SO 2 Effect of on the PNA efficacy of Ni-LTA-6

[0166] Water molecules (H 2O) has a large dipole moment and is always strongly adsorbed by zeolites, thereby deactivating the zeolites as adsorbents. For zeolite adsorbents used in PNA, the presence of H 2 O has been widely considered to have an adverse effect on the adsorption efficacy. To study the effect of H 2 O on NO adsorption / desorption under PNA conditions, breakthrough adsorption / desorption tests were conducted on Ni-LTA-6 (0.2 g loading) using wet NO / mixed gas with different concentrations of H 2 O vapor. As Figure 13A shown, an increase in the H 2 O concentration led to a significant decrease in the temperature at which NO breakthrough and desorption occurred. Since the efficiency of the downstream NO x reduction process was low, this change in the operating temperature was detrimental to the PNA process. This phenomenon may be mainly attributed to the competitive adsorption of H 2 O on the zeolite (due to its large dipole moment), thus potentially deactivating the adsorption sites for NO.

[0167] Another pollutant gas of concern in PNA is sulfur dioxide (SO 2 ), which is known to undergo tenacious adsorption that is difficult to desorb, resulting in the deactivation of the adsorbent. To evaluate the effect of SO 2 on the PNA performance of the Ni-LTA-6 adsorbent (0.2 g loading and 1.2 g loading) in this work, the material was subjected to a 10-hour pretreatment using a SO 2 stream (200 mL / min, 100 ppm SO 2 balanced with air) containing 2% H 2 O, followed by activation at 600 °C. As Figure 13B shown, the SO 2 pretreatment had no significant effect on the adsorption / desorption of NO in a NO / mixed gas containing 2% H 2 O. This finding strongly indicates that in this work, the functionality of the Ni-LTA-6 adsorbent is not affected by the presence of SO 2 in engine exhaust gases, indicating its resilience to SO 2 -induced deactivation.

[0168] Example 7

[0169] Ni-LTA-6 for wet engine exhaust in PNA

[0170] Based on the above situation, it is worth noting that Ni-LTA-6 exhibits remarkable performance in the PNA process under dry conditions, but its efficiency decreases under humid conditions. Given the inevitable significant water vapor content (up to 15%) in engine exhaust, the development of strategies for implementing Ni-LTA-6 in PNA under humid conditions was studied.

[0171] It is worth noting that PNA requires instantaneous adsorbent utilization during the cold start period, and H 2 O is hardly adsorbed at temperatures above 350 °C ( Figure 9A and 13A ). That is to say, this confirms that Ni-LTA-6 adsorbing H 2 O can be regenerated during engine preheating (250 - 450 °C) and steady-state operation (e.g., 450 - 600 °C). In other words, the amount of H 2 O adsorbed by Ni-LTA-6 during the cold start period was proven to be constant.

[0172] Therefore, the present inventors designed to deliberately load an excessive amount of Ni-LTA-6 for H 2 O adsorption (i.e., overloading the adsorbent for H 2 O adsorption), thereby promoting the adsorption of NO by Ni-LTA-6 under actual humid engine conditions. As Figure 14 depicted, it is worth noting that the performance of 1.2 g of Ni-LTA-6 exceeds that of 0.2 g of Ni-LTA-6, as evidenced by a significant increase in the NO adsorption / desorption temperature. Specifically, the temperature of NO breakthrough increased from 141 °C to 255 °C, while the temperature range of NO desorption increased from 160 - 200 °C to 260 - 420 °C.

[0173] By implementing this strategy, Ni-LTA-6 demonstrated its excellent ability to meet all the operational requirements of PNA. It is believed that compared with the reported PNA adsorbents, especially Pd-adsorbents, Ni-LTA-6 exhibits excellent NO adsorption ability because it can effectively prevent the breakthrough of NO below 200 °C in wet engine exhaust. This advantage is attributed to a higher achievable Ni 2+ loading (2 - 3 wt%) compared to Pd cations (usually less than 2 wt%), and faster Ni 2+ adsorption kinetics derived from π-backbonding compared to the reactive NO chemisorption derived from Pd cations.

[0174] In addition, it should be understood that the stability and regenerability of PNA adsorbents under actual scenarios have always been a challenge. After the vehicle is turned off, the tail gas flow stops, and the adsorbent needs to cool naturally. To evaluate the cyclic adsorption / desorption performance in humid simulated engine exhaust under simulated actual scenarios (including engine cold start, warm-up, steady-state operation, and shutdown), Ni-LTA-6 was naturally cooled between two cycles without dry He purge. In addition, during cooling, the column outlet was exposed to ambient air with a relative humidity of 60 - 70% to simulate the scenario of PNA adsorbent in the tailpipe.

[0175] As Figure 15 shown, the NO adsorption / desorption temperature window of Ni-LTA-6 remained unchanged over ten cycles, thus confirming its robust reusability under actual conditions. Ni-LTA-6 also exhibited excellent stability and regeneration ability under the actual scenarios of PNA. As Figure 16 shown, Ni-LTA-6 in humid simulated engine exhaust can be regenerated by temperatures above 430 °C. In addition, after 10 PNA cycles, the structure and crystallinity of Ni-LTA-6 remained unchanged (as evidenced by the identical synchrotron XRD patterns of Ni-LTA-6 before and after PNA cycles), which further demonstrated the excellent hydrothermal stability of Ni-LTA-6 ( Figures 17A to 17C ). Similarly, the well-dispersed isolated Ni 2+ sites in the cycled Ni-LTA-6 were evidenced by Ni K-edge XANES and EXAFS results ( Figure 18A and 18B ).

[0176] Based on the above, Ni-LTA-6 has excellent NO adsorption capacity and cost-effectiveness and is proven to be the most promising candidate for practical PNA, with great industrialization potential.

[0177] The present invention is given by way of example only, and various other modifications and / or alterations may be made to the described embodiments by those skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. A method for passive NO x The adsorbent comprises a small-pore zeolite having an eight-membered ring and non-noble metal ions introduced into the pores of the small-pore zeolite.

2. The adsorbent of claim 1, wherein the non-noble metal ions include Na + , K + Mg 2+ , Ca 2+ , Mn 2+ 、Co 2+ 、Ni 2+ , Cu 2+ 、Zn 2+ , Y 3+ ,La 3+ 、Ce 3+ 、Eu 3+ , Tb 3+ or Yb 3+ Any of .

3. The adsorbent according to claim 1, wherein the non-noble metal ions are selected from Na + Mg 2+ , Ca 2+ 、Co 2+ 、Ni 2+ and their combinations.

4. The adsorbent according to claim 1, wherein the eight-membered ring of the small pore zeolite is selected from any one of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, LTA, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON. The adsorbent according to claim 1 , wherein the small pore zeolite comprises a framework structure of any one of CHA and LTA.

6. The adsorbent of claim 5, wherein the framework structure of the LTA comprises a Si / Al ratio of 5.5 to 6.

7. The adsorbent according to claim 5, wherein the small pore zeolite comprises a framework structure of LTA-6.

8. The adsorbent according to claim 2, wherein the degree of ion exchange between the small pore zeolite and the non-noble metal ions is 20% to 104%.

9. The adsorbent of claim 8, wherein the small pore zeolite comprises a plurality of exchangeable sites, wherein the plurality of exchangeable sites are ion-exchangeable with the non-precious metal ions.

10. The adsorbent according to claim 1, which has a particle size of 0.5 mm.

11. The adsorbent according to claim 1, wherein the non-noble metal ion is Co 2+ and Ni 2+ Any one of the above, and the small pore zeolite has a framework structure of LTA-6.

12. The adsorbent according to claim 11, wherein the small pore zeolite is introduced with 5 wt% to 6 wt% Ni 2+ .

13. The adsorbent according to claim 11, wherein the small pore zeolite is introduced with 2 to 3 atomic % of Ni 2+ .

14. The adsorbent according to claim 11, wherein the small pore zeolite is introduced with 5 wt% to 6 wt% of Co 2+ .

15. The adsorbent according to claim 11, wherein the small pore zeolite is introduced with 2 to 3 atomic % of Co. 2+ .

16. The adsorbent according to claim 11, having a NO adsorption capacity of 0.22 mmol / g to 0.35 mmol / g at 80°C.

17. The adsorbent of claim 11, capable of capturing an effective amount of NO at a first temperature or below, and releasing substantially the same amount of captured NO at a second temperature above the first temperature.

18. The adsorbent of claim 17, wherein the first temperature is 183°C to 255°C.

19. The adsorbent of claim 17, wherein the second temperature is 195°C to 460°C.

20. The adsorbent according to claim 17, wherein the effective amount of NO is 200 ppm.

21. An exhaust system for an internal combustion engine comprising a passive NO x Adsorbers and exhaust treatment components, the passive NO x The adsorber contains the adsorbent as claimed in claim 1 , and the exhaust gas treatment component is arranged downstream of the adsorber and is in fluid communication with the adsorber.

22. The exhaust system of claim 21, wherein the adsorber is loaded with 0.2 g to 1.2 g of the adsorbent.

23. The tail gas system of claim 22, wherein the adsorber loaded with the adsorbent has a bed porosity of 70% to 80%.

24. The exhaust system of claim 21, wherein the adsorbent is thermally pretreated at a temperature of 300°C or above.

25. The exhaust system of claim 21, wherein the exhaust treatment component comprises a selective catalytic reduction (SCR) catalyst, a particulate filter, an SCR filter, a NO x At least one of an adsorbent catalyst, a three-way catalyst, and an oxidation catalyst.

26. A method for preparing the adsorbent according to claim 1, the method comprising the following steps: Provides NH4 + Ion or Na + Ionic small pore zeolites; and The small pore zeolite is added to a first solution containing a non-precious metal nitrate or a non-precious metal acetate to perform an ion exchange reaction, so that the NH4 + Ion or Na + The ions are replaced by the non-noble metal.

27. The method of claim 26, wherein the small pore zeolite comprises NH4 + LTA-6 or Na in ionic form + LTA-6 in ionic form.

28. The method of claim 27, wherein the NH4 + The solid / liquid ratio of the ionic form of LTA-6 to the first solution was 1 g / 50 mL.

29. The method of claim 27, wherein the Na + The solid / liquid ratio of the ionic form of LTA-6 to the first solution was 1 g / 100 mL.

30. The method of claim 26, wherein the non-precious metal comprises any one of Na, K, Mg, Ca, Mn, Co, Ni, Cu, Zn, Y, La, Ce, Eu, Tb, or Yb.

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