Pt / Mo / Al catalyst material and preparation method and application thereof

Abstract

The invention discloses a Pt / Mo / Al catalyst material and a preparation method and application thereof, and belongs to the technical field of material preparation and propane catalytic combustion. According to the invention, MoO3 modified Pt / Al2O3 is used as a model catalyst and is applied to a propane oxidation reaction. The MoO3 modified Pt / Al2O3 catalyst disclosed by the invention has the advantages that the interaction between surface acidity and a metal carrier is enhanced, and more metal Pt sites exist, so that an obvious promotion effect on a propane oxidation reaction is realized; some ideas are provided for designing a high-activity propane catalytic combustion catalyst in the future.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation and propane catalytic combustion, and specifically relates to a Pt / Mo / Al catalyst material and a preparation method and application thereof. Background Art

[0002] The emission of volatile organic pollutants (VOCs) poses a serious threat to human health and the ecological environment. With increasingly stringent pollution control regulations, how to achieve efficient removal of VOCs has received widespread attention. Since the core of catalytic combustion technology is the catalyst, designing catalysts with excellent catalytic performance, high stability and low cost has become one of the research hotspots in the field of environmental catalysis.

[0003] Generally, precious metals (such as Pt, Pd, Ru and Rh, etc.) supported on various supports (such as Al2O3, TiO2, CeO2 and molecular sieves, etc.) are the most commonly used catalysts for the catalytic combustion of VOCs. In order to further improve the supported precious metal catalysts, researchers have adopted various strategies. Considering that the precious metal sites play a key role in the reaction, these strategies mainly focus on regulating the state of precious metals and the interaction between metal supports. However, due to the complex catalyst preparation process, the strategy of regulating the state of precious metals and the interaction between metal supports is difficult to implement in industry. Therefore, researchers have conducted extensive research on simple modifications of supported precious metal catalysts.

[0004] In recent years, researchers generally believe that surface acidity plays a key role in the catalytic oxidation of VOCs. Guided by this understanding, a large number of studies have modified noble metal catalysts with acidic metals or inorganic acid groups by simple impregnation methods, and found that WO3 modification can promote the reduction of Pt species and induce CH bond activation on Pt / Al2O3 catalysts in propane oxidation reactions. In other words, acid modification may have an effect on noble metal catalysts in propane catalytic oxidation. However, to date, there is still a lack of a comprehensive discussion on the mechanism of this effect, especially based on traditional Pt group metal catalysts and commonly used acid modification strategies. Summary of the invention

[0005] The first technical problem to be solved by the present invention is to provide a Pt / Mo / Al catalyst material, which has excellent propane oxidation reaction performance; the second technical problem to be solved by the present invention is to provide a method for preparing the Pt / Mo / Al catalyst material, which is simple and easy to implement, has a small amount of waste by-products and a high product yield; the third technical problem to be solved by the present invention is to provide an application of a Pt / Mo / Al catalyst material in propane combustion, for propane combustion.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a Pt / Mo / Al catalyst material comprises the following steps: firstly preparing a Mo / Al carrier; then loading Pt by an incipient wetness impregnation method to prepare a Pt / Mo / Al catalyst.

[0008] The preparation method of the Mo / Al carrier is as follows: (NH4)6Mo7O 24 4H2O and commercial γ-Al2O3 were dissolved in deionized water and stirred; evaporated to dryness in an oil bath; then dried in an oven; and the resulting solid was calcined.

[0009] The oil bath temperature is 90°C; the drying temperature is 110°C, and the drying time is 4 h.

[0010] The calcination temperature is 550°C, the heating rate is 5°C / min, and the calcination time is 4 h.

[0011] The loading amount of MoO3 is 5-20 wt.%.

[0012] The preparation method of the Pt / Mo / Al catalyst is as follows: a Pt precursor salt is impregnated into a Mo / Al carrier, and then calcined to obtain a Pt / xMo / Al catalyst.

[0013] The Pt precursor is Pt(NO3)2; the loading amount of Pt is 1 wt.%.

[0014] The calcination temperature is 550°C, the heating rate is 5°C / min, and the calcination time is 2 h.

[0015] The Pt / Mo / Al catalyst material prepared by the method.

[0016] The application of the Pt / Mo / Al catalyst material in propane combustion.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention discloses a simple preparation process of MoO3 modified Pt / Al2O3 catalyst, which is simple and easy to operate, low in cost, has low waste by-product production and high product yield;

[0019] (2) The low-loaded Pt-based catalyst material prepared by the present invention has a Pt loading of ≤ 1 wt.%, which is lower than that of the materials reported by previous researchers and has better catalytic performance;

[0020] (3) The present invention fully considers the influence of the surface acidity of the carrier on the metal-carrier interaction and the state of the precious metal, which can improve the propane combustion activity of the Pt-based catalyst to a certain extent. Therefore, the Pt / Al2O3 catalyst material modified by simple MoO3 not only has good synthetic application value, but also has broad prospects in the field of practical catalytic applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD diagram of the sample prepared in the present invention; in the figure, (a) xMo / Al support; (b) Pt / xMo / Al;

[0022] Figure 2 This is the N2 adsorption-desorption isotherm diagram of the sample prepared in the present invention; in the figure, (a) xMo / Al carrier; (b) Pt / xMo / Al;

[0023] Figure 3 The pore size distribution diagram of the samples prepared in the present invention; in the figure, (a) xMo / Al support; (b) Pt / xMo / Al;

[0024] Figure 4 The Raman spectra of the samples prepared in the present invention are shown in FIG. 1 , (a) xMo / Al carrier; (b) Pt / xMo / Al;

[0025] Figure 5 This is the in-situ infrared spectrum of CO adsorption of the sample prepared by the present invention;

[0026] Figure 6 This is a CO temperature-programmed reduction diagram of the sample prepared in the present invention;

[0027] Figure 7 This is the XPS graph of the sample prepared in the present invention; in the figure, (a) Pt 4d; (b) Mo 3d;

[0028] Figure 8 NH3 programmed temperature desorption diagram of the sample prepared by the present invention;

[0029] Fig. 9 This is the pyridine adsorption infrared image of the sample prepared in the present invention;

[0030] Fig.10 Propane oxidation activity diagram of samples prepared for the present invention;

[0031] Fig.11 Stability graph of the samples prepared for the present invention evaluated in the presence of 5 vol.% H2O. DETAILED DESCRIPTION

[0032] The present invention is further illustrated below in conjunction with specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0033] Example 1

[0034] The method for preparing the Mo / Al carrier is as follows:

[0035] Weigh 92 mg, 184 mg, 276 mg and 368 mg of (NH4)6Mo7O 24 4H2O and 1 g of commercial γ-Al2O3 were dissolved in deionized water (MoO3 loadings were 5 wt.%, 10 wt.%, 15 wt.% and 20 wt.%, respectively) and stirred vigorously for 30 min. Subsequently, the mixture was evaporated to dryness in an oil bath at 90 °C. Next, the mixture was dried in an oven at 110 °C for 4 h. Finally, the obtained solid was calcined at 550 °C at a rate of 5 °C / min for 4 h.

[0036] Example 2

[0037] The method for preparing the Pt / Mo / Al catalyst is as follows:

[0038] 16.4 mg of Pt(NO3)2 precursor salt was weighed and impregnated into 1 g of Mo / Al carrier (Pt loading was 1 wt.%), and the temperature was raised to 550 °C at 5 °C / min and kept for 2 h. The obtained Pt catalyst was recorded as Pt / xMo / Al.

[0039] The samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms, pore size distribution, Raman spectra, CO adsorption in situ infrared spectroscopy, CO temperature-programmed reduction, X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption and pyridine adsorption infrared spectroscopy. The results are as follows:

[0040] Figure 1 Figure 2 is the XRD pattern of the prepared samples. When the MoO3 loading does not exceed 15 wt.%, no XRD peaks related to Mo species are observed on xMo / Al and Pt / xMo / Al, except for the XRD peaks attributed to γ-Al2O3. When the MoO3 loading reaches 20 wt.%, an XRD peak attributed to β-MoO3 (111) appears (PDF#47-1081). The γ-Al2O3 carrier (142 m 2 / g) of MoO3 without obvious agglomeration, and the maximum loading of MoO3 was 15-20 wt.%. No crystalline Pt species were observed on all Pt / Al and Pt / xMo / Al catalysts, and the surface Pt was highly dispersed.

[0041] Figure 2 and Figure 3 These are the adsorption / desorption isotherms and pore size distribution diagrams of xMo / Al and Pt / xMo / Al, respectively. Since Mo and Pt species are highly dispersed on Pt / xMo / Al, the isotherm type and pore size of the γ-Al2O3 support remain almost unchanged after Mo and Pt deposition.

[0042] Figure 4 Figure 2 shows the Raman spectra of xMo / Al and Pt / xMo / Al, where peak α and peak β are related to the symmetric stretching vibration of Mo-O and the asymmetric stretching vibration of Mo=O, respectively. For xMo / Al, the peak area ratio of peak β to peak α (β / α) gradually decreases with the increase of MoO3 loading, indicating that Mo=O bonds polymerize into Mo-O-Mo bonds and form polymolybdates. After depositing Pt on xMo / Al, the value of β / α is further reduced, indicating that the deposited Pt species interacts with Mo=O, resulting in the generation of Pt-O-Mo bonds and strong Pt-Mo interactions.

[0043] Figure 5 In situ infrared spectra of CO adsorption on Pt / Al and Pt / Mo / Al. For Pt / Al, the CO adsorption peaks at 2092 and 2037 cm -1 Two ions were observed at the Pt δ+ CO at the site (CO-PtO x ) and adsorbed on Pt 0 CO at the site (CO-Pt 0 ). CO-PtO x and CO-Pt 0 The coexistence of peaks means that the Pt species on Al2O3 are clusters or nanoparticles. 0 The intensity of the peak is enhanced, indicating that the Pt formed on Pt / xMo / Al is 0 In addition, when the MoO3 loading increases to 10 wt.% or higher, the -1 A new broad peak appears at , which is attributed to the aggregated Pt species adsorbed on Pt 0 The bridging CO on the site indicates that more MoO3 leads to more surface Pt on Pt / xMo / Al. 0 Location.

[0044] Figure 6The CO programmed temperature reduction test results of the prepared samples. For Al2O3, no obvious CO consumption peak was observed in the range of 50-700 ℃. After MoO3 deposition, a CO consumption peak at 632 ℃ was observed, which may be related to the reduction of MoO3. Two CO consumption peaks at 256 ℃ and 455 ℃ appeared on the CO ascending temperature reduction curve of Pt / Al, which were attributed to the reduction of Pt-O and Pt-O-Al species. After MoO3 modification, the reduction temperature of Pt-O decreased (from 256 ℃ to 228 ℃), indicating that Mo can promote the reduction of Pt δ+ Species reduction. The CO consumption peak intensity of Pt-O species on Pt / 15Mo / Al is relatively low compared with that on Pt / Al, indicating that the average valence state of Pt species is lower. In addition, the strong CO consumption peak caused by Pt-O-Mo reduction at 355 °C also confirms the formation of a strong Pt-Mo interaction on Pt / 15Mo / Al.

[0045] Figure 7 The XPS test results of Pt / Al and Pt / Mo / Al are shown in Figure 2. For Pt 4d XPS, the peaks at about 314.3 and 331.3 eV are attributed to Pt 0 The peaks at about 317.4 and 334.4 eV are attributed to Pt 4+ According to the fitting analysis results, Pt / Al 0 The Pt / 15Mo / Al produced more metallic Pt species, Pt 0 The proportion increased to 37%. Figure 7 b is the Mo 3d XPS of 15Mo / Al and Pt / 15Mo / Al. The peaks of 15Mo / Al centered at 236.4 eV (Mo 3d3 / 2) and 233.3 eV (Mo 3d5 / 2) indicate that the Mo species on 15Mo / Al are mainly Mo 6+ Pt deposition onto 15Mo / Al causes the Mo 3d XPS (0.2 eV) to shift to a higher binding energy, indicating that Mo species can donate electrons to Pt sites through Pt-O-Mo bonds, leading to the formation of electron-rich Pt species.

[0046] Figure 8 The results of NH3 temperature programmed desorption on Pt / Al and Pt / Mo / Al. The amount of NH3 adsorbed on 15Mo / Al (252 μmolNH3∙g cat . -1 ) is almost Al2O3 (59 μmol NH3∙g cat . -1), indicating that Mo modification can significantly improve the surface acidity of Al2O3. After Pt is deposited on Al2O3 and 15Mo / Al, the NH3 desorption peak is enhanced at low temperature (about 100 ℃) and weakened at high temperature (about 400 ℃), which may be related to the weak adsorption of NH3 on Pt sites and the strong interaction between Pt and Mo sites.

[0047] according to Fig. 9 The infrared results of pyridine adsorption show that for Al2O3 and Pt / Al, the surface acid sites are mainly L acid. For 15Mo / Al and Pt / 15Mo / Al, the infrared peaks attributed to pyridine adsorbed on the B acid sites can be clearly observed, and compared with Al2O3 and Pt / Al, the infrared peaks at 1489 cm -1 The peak intensity of is also enhanced, indicating that the introduction of MoO3 leads to the generation of abundant B acid sites on Al2O3.

[0048] Example 3

[0049] The Pt / Mo / Al catalyst prepared in Examples 1-2 was applied to the propane catalytic combustion reaction. The propane catalytic combustion reaction activity test was evaluated on a fixed bed quartz tube reactor. The specific steps are as follows:

[0050] A certain amount of catalyst (40-60 mesh) mixed with SiC (the mass ratio of catalyst to SiC was 1:5) was loaded into a quartz tube reactor and pretreated with high-purity air (30 mL / min) at 300 °C for 1 h. The catalyst dosage was 60 mg, and the reaction gas (100 mL / min) consisted of 4000 ppm C3H8 and 5% O2, with Ar as the balance gas, and a WHSV of 100,000 mL∙g cat -1 ∙h -1 The propane conversion rate in the propane oxidation reaction is calculated according to the following formula:

[0051]

[0052] Fig.10 The results show that Mo doping can significantly improve the catalytic performance of Pt / Al in propane oxidation reaction, and the optimal MoO3 loading of Pt / xMo / Al is 15 wt.% (T 50 = 242 ℃). This phenomenon suggests that surface MoO3 modification will affect the surface acidity of Pt / Al2O3 catalysts, metal-support interactions, and Pt species state, thus affecting propane combustion activity.

[0053] Fig.11To evaluate the stability of the prepared samples in the presence of 5 vol.% H2O. The results show that the introduction of 5 vol.% H2O will deactivate the Pt / Al and Pt / 15Mo / Al catalysts in propane oxidation. However, the T 50 (25 ℃) compared with Pt / 15Mo / Al, T 50 The increase is small, indicating that Mo modification can enhance the H2O tolerance of Pt / Al catalysts.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a Pt / Mo / Al catalyst material, characterized in that: First, a Mo / Al carrier was prepared; then Pt was loaded by an incipient wetness impregnation method to prepare a Pt / Mo / Al catalyst.

2. The method for preparing the Pt / Mo / Al catalyst material according to claim 1, characterized in that: The preparation method of the Mo / Al carrier is as follows: (NH4)6Mo7O 24 4H2O and commercial γ-Al2O3 were dissolved in deionized water and stirred; evaporated to dryness in an oil bath; then dried in an oven; and the resulting solid was calcined.

3. The method for preparing the Pt / Mo / Al catalyst material according to claim 2, characterized in that: The oil bath temperature is 90°C; the drying temperature is 110°C, and the drying time is 4 h.

4. The method for preparing the Pt / Mo / Al catalyst material according to claim 2, characterized in that: The calcination temperature is 550°C, the heating rate is 5°C / min, and the calcination time is 4 h.

5. The method for preparing the Pt / Mo / Al catalyst material according to claim 2, characterized in that: The loading amount of MoO3 is 5-20 wt.%.

6. The method for preparing the Pt / Mo / Al catalyst material according to claim 1, characterized in that: The preparation method of the Pt / Mo / Al catalyst is as follows: a Pt precursor salt is impregnated into a Mo / Al carrier, and then calcined to obtain a Pt / xMo / Al catalyst.

7. The method for preparing the Pt / Mo / Al catalyst material according to claim 6, characterized in that: The Pt precursor is Pt(NO3)2; the loading amount of Pt is 1 wt.%.

8. The method for preparing the Pt / Mo / Al catalyst material according to claim 6, characterized in that: The calcination temperature is 550°C, the heating rate is 5°C / min, and the calcination time is 2 h.

9. The Pt / Mo / Al catalyst material prepared according to the method according to any one of claims 1 to 8.

10. Use of the Pt / Mo / Al catalyst material according to claim 9 in propane combustion.

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