Samarium-zirconium-deficient fluorite-type nickel-based catalyst for hydrogen production by autothermal reforming of acetic acid

Abstract

The present application relates to a kind of for the hydrogen production of acetic acid autothermal reforming samarium zirconium defect fluorite type nickel-based catalyst.The present application is directed to the problem of existing catalyst structure easy sintering and carbon deposition etc., which leads to catalyst deactivation, provide a new catalyst with stable structure, high activity.The molar composition of the catalyst of the present application is as follows: a (SmO 1.5 ) b (ZrO2) c Wherein a is 0.79-0.82, b is 1.13-1.16, c is 1.13-1.16.The present application uses coprecipitation method to prepare catalyst precursor, after calcination, reduction, the defect fluorite type nickel-based catalyst containing Ni and Sm2Zr2O7 is obtained, which effectively improves the hydrogen production rate and catalyst structure stability, and has anti-sintering ability and anti-carbon deposition ability.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of samarium zirconium defect fluorite type nickel-based catalyst for the self-thermal reforming of acetic acid and its preparation method, belong to the field of hydrogen production by the self-thermal reforming of acetic acid. BACKGROUND

[0002] Hydrogen is a clean renewable energy carrier, which can be produced by electrolysis of water, natural gas conversion, biomass conversion and other ways. Biomass hydrogen production utilizes renewable biomass resources, and is a promising way to obtain green hydrogen. The yield of direct hydrogen production from biomass is low, and the biomass oil is often obtained by fast pyrolysis of biomass. The inexpensive biomass oil-water phase components are separated, and then the main component of water phase, acetic acid, is obtained as a good inexpensive hydrogen production raw material.

[0003] Acetic acid can be hydrogenated by traditional steam reforming process, while the traditional steam reforming reaction is an endothermic reaction (CH3COOH+2H2O→2CO2+4H2, ΔH=+131.4 kJ / mol). In order to make the reaction continue, heat needs to be continuously obtained from the outside world. The partial oxidation reaction of acetic acid introduces oxygen and acetic acid as raw materials, which is an exothermic reaction, but the hydrogen production rate is low. The self-thermal reforming reaction of acetic acid (CH3COOH+aO2+bH2O→cCO+dCO2+eH2, ΔH=0 kJ / mol) combines the above two ways of producing hydrogen, and introduces water vapor and oxygen or air. By controlling the ratio of oxygen to reactants and balancing the heat supply of the reaction system, self-heating is achieved, which has significant advantages.

[0004] In the process of hydrogen production by self-thermal reforming of acetic acid, nickel-based catalysts have the ability to activate C-C and C-H bonds and can be applied in this process. However, in the process of hydrogen production by self-thermal reforming of acetic acid, on the one hand, oxygen is introduced into the raw materials, and oxidation reaction easily occurs at the front end of the catalyst bed, making the local temperature reach above 1000℃, which leads to the aggregation and sintering of the catalyst. On the other hand, in the process of hydrogen production by self-thermal reforming of acetic acid, acetic acid reforming reaction, water gas shift reaction and acetic acid thermal cracking reaction are the main reactions. Water gas shift reaction and acetic acid thermal cracking reaction produce the same amount of hydrogen, but also produce CO, CO2, C2H4, CH2CO and other C-containing products. CO and CO2 will continue to undergo methanation reaction, CH2CO will undergo polymerization reaction, etc., producing C* and other intermediate species, forming carbon deposition and covering on the active component nickel, resulting in the decrease or even inactivation of the catalyst activity.

[0005] Therefore, for the problems of carbon deposition, oxidation and sintering of the autothermal reforming process, improving the carbon deposition resistance, oxidation resistance and sintering resistance of the nickel-based catalyst is the key to improve the reaction activity and selectivity of hydrogen production by acetic acid autothermal reforming.

[0006] To solve the above problems, the present application introduces Sm and Zr components according to the characteristics of the acetic acid autothermal reforming conversion process, and creates a Sm2Zr2O7 samarium-zirconium defective fluorite type nickel-based catalyst with Ni as the active component by using the coprecipitation method.

[0007] Firstly, in the catalyst of the present application, the composite oxide Sm2Zr2O7 with a defective fluorite structure is used as the carrier of Ni, forming a strong interaction between the nickel species and the carrier, enhancing the dispersion and thermal stability of the Ni active sites, and improving the activity, stability and carbon deposition resistance of the catalyst; secondly, the ratio of the ionic radii of samarium and zirconium is less than 1.46, the carrier Sm2Zr2O7 forms a defective fluorite phase belonging to the Fm-3m space group, and the samarium and zirconium cations are uniformly distributed in the sublattice, while the oxygen species in the anion sublattice is distributed in disorder, thereby resulting in more surface active oxygen species; thirdly, the introduced Sm and Zr elements have the ability of multi-valence electron transfer, and construct two kinds of redox electron pairs, Zr 4+ / Zr 3+ and Sm 3+ / Sm 2+ under the oxygen atmosphere, the formation of the electron pairs promotes the charge circulation in the acetic acid autothermal reforming reaction process, effectively promotes the reduction of Ni metal, thereby exposing more active sites, promoting the bond breaking of the reactant acetic acid molecules and the conversion of the carbon-containing intermediate products generated thereby, and improving the gasification ability of the carbon deposition precursor CH x * / C* and inhibiting carbon deposition; finally, the samarium-zirconium defective fluorite type nickel-based catalyst prepared by the coprecipitation method is a mesoporous material, and the porous structure thereof is beneficial to the diffusion and transmission of the product molecules and the reactant molecules, is beneficial to increasing the dispersion of Ni, inhibits the polymerization of the acetic acid autothermal reforming hydrogen production carbon deposition precursor ethylene ketone, and reduces the formation of carbon deposition.

[0008] The innovation of the catalyst composition and structure of the present application enables the catalyst to exhibit good activity, stability and carbon deposition resistance, oxidation resistance and sintering resistance in the acetic acid autothermal reforming reaction, and to improve the selectivity of hydrogen, thereby exhibiting the characteristics of an excellent catalyst. SUMMARY

[0009] The technical problem to be solved by the present application is to provide a novel catalyst with stable structure, high conversion rate and good selectivity, in view of the problems of poor stability, easy carbon deposition, oxidation and sintering of the active component of the existing catalysts in the acetic acid autothermal reforming reaction, which leads to the decrease of the catalyst activity and even deactivation.

[0010] The present application uses Ni as an active component, introduces Sm2Zr2O7 samarium-zirconium defect fluorite structure as a carrier, and prepares a nickel-based catalyst by using a coprecipitation method; the catalyst is used in an acetic acid autothermal reforming reaction for hydrogen production, and in the case that the reaction temperature is 700 DEG C, the conversion rate of the catalyst acetic acid is close to 100%, and the hydrogen production rate is stably around 2.4 mol-H2 / mol-HAc.

[0011] The technical scheme of the present application is as follows:

[0012] The present application is directed to the characteristics of acetic acid autothermal reforming, and a Ni / Sm2Zr2O7 catalyst is prepared by using a coprecipitation method. The molar composition of the catalyst is (NiO) a (SmO 1.5 ) b (ZrO2) c , wherein a is 0.79-0.82, b is 1.13-1.16, and c is 1.13-1.16; the weight percentage composition is as follows: nickel oxide is 14.0%-16.0%, samarium sesquioxide is 49.2%-50.4%, zirconium dioxide is 34.8%-35.6%, and the sum of the weight percentages of the components is 100%.

[0013] The specific preparation method steps are as follows:

[0014] 1) preparing a mixed solution of metal nitrates: a certain amount of nickel nitrate hexahydrate, samarium nitrate and zirconyl nitrate is weighed according to a certain molar ratio, and is dissolved in water to form a mixed nitric acid solution 1#;

[0015] 2) preparing a precipitant: according to the molar ratio [OH - ] / [Sm 3+ +Zr 4+ ]=1 / 8 and [OH - ] / [CO3 2- ]=1 / 16, Na2CO3 and NaOH are weighed to prepare a precipitant, and are dissolved in deionized water to form a mixed solution 2#;

[0016] 3) simultaneously adding 1# and 2# solutions to a beaker, keeping the temperature at about 65 DEG C, controlling the solution pH at 10.5±0.5, and continuously stirring to perform a coprecipitation reaction, after titration, stirring the solution and aging for 24 hours;

[0017] 4) after aging, the precipitate is obtained by 3 times of suction filtration and washing, and is immediately transferred into a 105 DEG C oven for drying for 24 hours to obtain a catalyst precursor;

[0018] 5) The obtained precursor is calcined at a temperature raising rate of 10°C / min to 900°C and at this temperature for 4h, to obtain the NiO / Sm2Zr2O7 catalyst of the present application, whose main components are NiO and Sm2Zr2O7, as shown in the X-ray diffraction pattern (Figure 1), and which has a mesoporous structure, as shown in the BJH desorption average pore size distribution (Figure 2); Figure 3 Figure 2

[0019] 6) The catalyst is activated by reduction in H2 at 600-800°C for 1h before the self-thermal reforming reaction of acetic acid, to obtain the Ni / Sm2Zr2O7 catalyst, in which the metal nickel is supported on the samarium-zirconium defective fluorite structure, as shown in the X-ray diffraction pattern (Figure 3), and in which the Ni-Sm-Zr-O Figure 1 x active center is formed; the mixed gas with a molar ratio of acetic acid / water / oxygen / nitrogen = 1 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5) is introduced into the catalyst bed, and the reaction is carried out at a temperature of 600-800°C.

[0020] Advantages of the present application:

[0021] 1) The catalyst of the present application uses Ni as the active component, and introduces Sm2Zr2O7 as the carrier by co-precipitation, to form the stable Ni / Sm2Zr2O7 catalyst, and the Ni-Sm-Zr-O x active center is formed. The catalyst of the present application exhibits good selectivity, catalytic activity and oxidation resistance in the hydrogen production by self-thermal reforming of acetic acid, and the acetic acid conversion rate of the preferred catalyst is about 100%, and the hydrogen production rate is about 2.4 mol-H2 / mol-HAc.

[0022] 2) The catalyst of the present application introduces the carrier Sm2Zr2O7, and since the Sm / Zr ion radius ratio is less than 1.46, a defective fluorite phase belonging to the Fm-3m space group is formed, and Sm and Zr are uniformly dispersed in the sublattice, while the oxygen species in the anion sublattice is arranged in disorder, and has a high lattice oxygen mobility and a rich oxygen vacancy, thereby generating more surface active oxygen species, improving the oxygen storage capacity of the catalyst, and further promoting the gasification conversion capacity of the CH2CO and C* etc. carbon precursor produced by the self-thermal reforming of acetic acid, and effectively improving the carbon deposition resistance of the catalyst.

[0023] 3) The Sm2Zr2O7 carrier formed by the catalyst of the present application is a material with good thermal stability and mechanical stability, and the composite oxide Sm2Zr2O7 with a defective fluorite structure is used as the carrier of Ni, and a strong interaction is formed between the metal nickel and the Sm2Zr2O7 carrier, which enhances the dispersity and thermal stability of the Ni active site, and forms the Ni-Sm-Zr-O x ​​​The active center provides a stable reaction interface, exposes more active sites, and is conducive to the adsorption and conversion of CH3COOH, H2O and O2 into H2 and other products; in addition, Sm2Zr2O7 has rich oxygen vacancies, and the Zr 4+ / Zr 3+ and Sm 3+ / Sm 2+ Under the action of the redox pair, electrons are transferred through the Sm-O-Zr bridge, further increasing the surface oxygen defects, promoting the bond breaking of the acetic acid molecules and the conversion of the carbon-containing intermediate products generated thereby, and improving the gasification capacity of CH x * / C* carbon precursor, the activity, stability and anti-coking performance of the catalyst.

[0024] 4) The catalyst Ni / Sm2Zr2O7 of the present application has a mesoporous structure, which is conducive to the transmission and diffusion of the reactant molecules, increases the dispersion of Ni, and improves the activity of the catalyst; and through the confinement effect of the mesoporous structure, the condensation and carbon formation of intermediate species such as CH2CO and CH3OCH3 are effectively inhibited, and the selectivity to the reaction products H2 and CO / CO2 is improved.

[0025] 5) The results of the acetic acid autothermal reforming reaction show that in the conversion of acetic acid, the catalyst of the present application has high conversion of acetic acid, high hydrogen yield, and effectively inhibits the generation of by-products, and has excellent properties such as stability, anti-coking, anti-oxidation, anti-sintering, etc. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 : X-ray diffraction spectrum of the catalyst of the present application

[0027] Figure 2 : BJH pore size distribution graph of the catalyst of the present application

[0028] Figure 3 : X-ray diffraction spectrum of the oxidized state of the catalyst of the present application DETAILED DESCRIPTION

[0029] Reference Example One

[0030] Take 24.99 g of Al(NO3)3·9H2O and 2.33 g of Ni(NO3)2·6H2O into separate beakers, add a certain amount of deionized water to dissolve, and obtain solution 1#; then take 8.34 g of sodium hydroxide and 1.38 g of anhydrous sodium carbonate, dissolve and mix to obtain solution 2#; under the conditions of 65°C and pH 10.5±0.5, slowly add solution 1# and solution 2# for coprecipitation reaction, and keep the temperature and stirring aging for 24 h; after 3 times of suction filtration and washing, the precipitate is obtained, and then it is transferred into a 105°C oven for drying for 24 h, the catalyst precursor is obtained, which is transferred into a tube furnace to rise to 700°C at a temperature rising rate of 10°C / min, and kept for 4 h to obtain the CDUT-NA catalyst, which is a Ni-based catalyst supported on Al2O3; the weight percentage composition of the catalyst in terms of oxides is: 15.1% of nickel oxide (NiO) and 84.9% of aluminum oxide (AlO 1.5 ).

[0031] The activity evaluation of the acetic acid autothermal reforming reaction was carried out in a continuous flow fixed bed reactor. The catalyst was ground and tabletted, and then sieved into 20-40 mesh particles, 0.1-0.2 g of which was loaded into the reactor and reduced in H2 at a temperature of 600-800°C for 1 h; then a mixed solution of acetic acid and water was injected into a vaporizer by a constant flow pump, mixed with oxygen, and nitrogen was used as an internal standard gas to form a reaction raw gas with a molar composition of CH3COOH / H2O / O2 / N2 = 1 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5), and the raw gas was introduced into the reaction bed layer, and the reaction conditions were 600-800°C, atmospheric pressure, space velocity 10000-35000 mL / (g catalyst ·h), and the tail gas was analyzed online by a gas chromatograph.

[0032] The activity of the catalyst CDUT-NA in acetic acid autothermal reforming was investigated, and under the reaction conditions of atmospheric pressure, space velocity 25000 mL / (g catalyst ·h), reaction temperature 700°C, and raw gas acetic acid / water / oxygen = 1 / 4.0 / 0.28, the conversion rate of acetic acid decreased from 93.5% to 64.6% in 10 hours of activity experiment, and the hydrogen production rate also decreased from 2.27 mol-H2 / mol-HAc to 0.78 mol-H2 / mol-HAc; the low hydrogen production rate was not only due to the low conversion rate of acetic acid, but also because the selectivity of the byproduct acetone increased to about 41.2%, indicating that the ketone reaction of acetic acid mainly occurred during the experiment; the characterization results of XRD, BET, etc. showed that the catalyst had poor stability in the process of acetic acid autothermal reforming, and there were many byproducts, the acetone reaction was not effectively inhibited, sintering, carbon deposition and partial oxidation occurred, and the activity was low.

[0033] Example 1

[0034] Take 5.08 g of Sm(NO3)2, 2.64 g of ZrO(NO3)2·9H2O and 2.33 g of Ni(NO3)2·6H2O, pour into a beaker, add a certain amount of deionized water to dissolve, mix to obtain solution 1#; then take 5.93 g of sodium hydroxide and 1.03 g of anhydrous sodium carbonate, dissolve and mix to obtain solution 2#; slowly add solution 1# and solution 2# under the condition of 65℃, pH 10.5±0.5, carry out coprecipitation reaction, and keep temperature stirring and aging for 24 h; after 3 times of suction filtration and washing, the precipitate is obtained, and then it is immediately transferred into a oven at 105℃ for drying for 24 h, the catalyst precursor is obtained, it is transferred into a tube furnace to rise to 900℃ at a temperature rising rate of 10℃ / min, and keep for 4 h, the CDUT-NSZ11 catalyst is obtained, which forms a NiO / Sm2Zr2O7 catalyst, and its typical crystal structure is shown in the attached figure 1, there are strong defect-fluorite Sm2Zr2O7 diffraction peaks at the positions of 29.2°, 33.9°, 48.5°, 57.8°, 60.6°, 71.1°, 78.5° of the diffraction spectrum, and NiO diffraction peaks appear at 37.4°, 43.4°, 63.0°, 75.8°; after the sample is reduced by hydrogen at 600-800℃, the crystal structure is shown in the attached figure 2, the defect-fluorite Sm2Zr2O7 peaks remain stable, and Ni metal diffraction peaks are formed, and a Ni-Sm-Zr-O Figure 3 Figure 1 x The Ni / Sm2Zr2O7 catalyst with Ni as active center has the following composition in terms of weight percentage of oxides: 15.0% of nickel oxide, 49.8% of samarium sesquioxide, and 35.2% of zirconium dioxide.

[0035] The activity of the catalyst CDUT-NSZ11 in acetic acid autothermal reforming is investigated, and the results show that under the reaction conditions of normal pressure, space velocity of 25000 mL / (g catalyst ·h), reaction temperature of 700℃, and raw gas acetic acid / water / oxygen = 1 / 4.0 / 0.28, the initial conversion rate of acetic acid is close to 100%, the hydrogen production rate is 2.42 mol-H2 / mol-HAc, the selectivity of CO2 is about 49.4%, the selectivity of CO is about 50.6%, and there is no byproduct methane and acetone; with the reaction proceeding, the hydrogen production rate is stable at about 2.40 mol-H2 / mol-HAc, and the acetic acid conversion rate remains at 100% in the ten-hour activity experiment. The characterization results of XRD, BET, etc. show that the specific surface area of the catalyst is 48.101 m 2 / g, and the pore volume is 0.032 cm 3 ​​The average pore size is 2.671 nm, and the catalyst is a mesoporous material; the catalyst has good stability in the self-heat reforming process of acetic acid, is resistant to carbon deposition, oxidation and sintering, and the Sm2Zr2O7 carrier stably exists before and after the reaction, thereby providing stable reaction sites for the reaction.

Claims

1. The application of samarium-zirconium defective fluorite-type nickel-based catalysts in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: 0.1-0.2 g of catalyst was weighed and reduced in H2 at 600-800 °C for 1 h. After purging with nitrogen, a mixed solution of acetic acid and water was injected into a vaporizer using a constant flow pump. After vaporization, oxygen was mixed in, and nitrogen was used as an internal standard gas to form a reaction feed gas with a molar composition of CH3COOH / H2O / O2 / N2 = 1 / (1.3-5.0) / (0.21-0.35) / (2.5-4.5). This feed gas was introduced into the reaction bed, and the reaction temperature was 600-800 °C. The catalyst was prepared by the following method: a certain amount of nickel nitrate, zirconium oxynitrate, and samarium nitrate were weighed and dissolved in water to form a mixed nitric acid solution 1#; a certain amount of sodium carbonate and sodium hydroxide were weighed and dissolved in deionized water to form a mixed solution 2#; solutions 1# and 2# were added dropwise to a beaker, and the temperature was maintained at 65 °C. The solution pH was controlled at 10.5±0.5, and the co-precipitation reaction was carried out with continuous stirring. Stirring was maintained for 24 h, followed by aging. After aging, the precipitate was obtained by three filtrations and washings, and then dried in an oven at 105 ℃ for 24 h to obtain the catalyst precursor. The dried sample was placed in a tube furnace and heated from room temperature to 900 ℃ at a rate of 10 ℃ / min, and calcined for 4 hours to obtain the NiO / Sm2Zr2O7 structure. After reduction with hydrogen at 600-800 ℃, a Ni-Sm-Zr-O structure was obtained on a Ni-metal particle-supported defective fluorite Sm2Zr2O7 support. x The catalyst is a Ni / Sm2Zr2O7 catalyst with the active center, wherein the Sm2Zr2O7 support is a defective fluorite phase belonging to the Fm-3m space group; the molar composition of the catalyst of this invention, based on oxides, is (NiO). a (SmO 1.5 ) b (ZrO2) c The composition of nickel oxide is as follows: nickel oxide is 14.0%-16.0%, samarium oxide is 49.2%-50.4%, and zirconium dioxide is 34.8%-35.6%, with the total weight percentage of each component being 100%.

2. The application of the samarium-zirconium defect fluorite-type nickel-based catalyst according to claim 1 in the autothermal reforming of acetic acid to produce hydrogen, characterized in that: The catalyst has the following composition by weight percentage of oxides: nickel oxide 15.0%, samarium trioxide 49.8%, and zirconium dioxide 35.2%.

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