PL234050B1 - Method for obtaining a catalyst for steam reforming of methanol and the catalyst obtained by this method - Google Patents

Abstract

The subject of the application is a method for preparing a catalyst involving zinc and palladium salts, deposited on a zinc and chromium oxide support, useful for hydrogen production in methanol steam reforming reactions, as well as a catalyst prepared by this method. The method is characterized in that the dried zinc and chromium oxide support is mixed with an alkaline or neutral impregnation solution, used in excess, in the form of near-saturated solutions of palladium and zinc compounds, excluding halogen salts, in which the percentage of palladium ions is more than 3% by weight per unit weight of the support, and the molar concentration of zinc ions is two to four times greater than the molar concentration of the corresponding palladium salt used, after which the solvent is evaporated until a wet, solid catalyst is obtained. The resulting catalyst is conditioned, dried, and calcined to obtain palladium and zinc oxides, which are then pre-activated with a reducing gas until the active centers are obtained in the form of metallic palladium or a palladium-zinc alloy. The application also concerns a catalyst for steam reforming methanol, obtained by the method of the invention, the use of which increases methanol conversion and reduces carbon monoxide formation compared to catalysts known in the art.

Description

Description of the invention

The subject of the invention is a method of obtaining a catalyst with the use of zinc and palladium salts, deposited on a support in the form of zinc and chromium oxides, the use of which in methanol steam reforming reactions increases methanol conversion and reduces the formation of carbon monoxide in relation to the catalysts known in the art.

Hydrogen is widely used in the chemical and refining industries. The demand for hydrogen also appears in the field of highly processed compounds technology, e.g. for selective hydrogenation reactions. Hydrogen is also used to power fuel cells that produce electricity. Currently, the most important methods of hydrogen production include the catalytic conversion of hydrocarbons with steam (steam reforming), mainly of natural gas (methane) and partial oxidation of hydrocarbons. For the production of hydrogen in dispersed small stationary or mobile units for fuel cell applications, it is advantageous to use liquid feedstocks that can be easily stored, transported and processed on site. An attractive carrier of hydrogen with such properties is methanol and its reaction with water - methanol steam reforming.

CH3OH + H2O 3H2 + CO2

During such a process, side and secondary reactions may take place, leading to changes in selectivity and formation of carbon monoxide.

CH3OH 2H2 + CO CO H2O θ CO2 + H2

The proportion of the individual reaction products depends on the type of catalyst and the reaction temperature. The most commonly used methanol steam reforming catalysts are copper catalysts with ZnO as the basic component of the support. In many patents and scientific publications, e.g. S. Sa, H. Silva, L. Brandao, J.M. Sousa, A, Mendes, Catalysts for methanol steam reforming. A review, Applied Catalysis B: Environmental 99 (2010) 43-57 and S.T. Yong, C.W. Ooi, S.P. Chai, X.S. Wu, Review of methanol reform ing-Cu-based catalysts, surface reaction mechanisms, and reaction schemes, International Journal of Hydrogen Energy, (2013) 9541-9552, systems modified with Al, Zr, La, Ce or Cr are described. For the most part, catalyst systems containing copper are characterized by high pyrophoricity and insufficient resistance to frequent changes in the system's work cycles.

Known, e.g. from the publication of N. Takezawa, N. Iwasa, Steam reforming and dehydrogenation of methanol: Difference in the catalytic functions of copper and group VIII metals, Catalysis Today 36 (1997) 45-56, S. Sa, H. Silva , L. Brandao, JM Sousa, A. Mendes, Catalysts for methanol steam reforming. A review, Applied Catalysis B: Environmental 99 (2010) 43-57, Y. Suwa, S. Ito, S. Kameoka, K. Tomishige, K. Kunimori, Comparative study between Zn-Pd / C and Pd / ZnO catalysts for steam reforming of methanol, Applied Catalysis A: General 267 (2004) 9-16 and L. Yang, GD Lin, H.B. Zhang, Highly efficient Pd-ZnO catalyst doubly promoted by CNTs and SC2O3 for methanol steam reforming, Applied Catalysis A: General 455 (2013), 137-144, the second group of methanol steam reforming catalysts, are supported platinum and palladium catalysts on oxide-containing supports zinc, to a lesser extent gallium or indium oxides, which may contain simultaneously various modifiers such as titanium, chromium, molybdenum, vanadium, manganese, nickel, bismuth, lanthanum, cerium, gadolinium, and samarium. They do not have pyrophoric properties and show similar activity and selectivity to copper catalysts. JP 57007255 describes catalysts obtained by two-stage impregnation of moldings containing zirconium and aluminum oxides and one or two metals or their oxides from the group of Cu, Zn, Cr, Fe, Co, Ni, Pt or Pd. In turn, from US 6,413,449, US 6,936,237, catalysts for alcohol reforming containing active ingredients are known, such as, for example, Pd-Zn alloy deposited on a ZnO carrier or other carriers containing at least one of the components or a mixture of aluminum oxide, silicon oxide, aluminum silicate , titanium oxide, zirconium oxide, zeolite, lanthanum oxide, as well as palladium catalysts with a zinc oxide support or catalysts with active ingredients such as Pd-Ru, Pd-Zn, Cu, Pd, Zn, Ru on Al2O3, ZrO2 support , on aluminum oxide or zirconium with added cerium.

The patent description WO2007019361 mentions a palladium catalyst for the production of hydrogen for fuel cells in the steam reforming reaction of methanol, containing palladium in an amount of at least 0.05% by weight, deposited on lanthanide oxides (Ce, La) and transition metals (Fe, Cr or Me).

As disclosed in the patent specification CN101053833, in the high-temperature steam reforming reaction of methanol (350-450 ° C), low percent Pall catalysts are used.

Dioxide (less than 0.6%) deposited on metal oxides from the lanthanide group (La, Ce, Gd, Sm) and on oxides of transition metals such as Ti, Cr, Mo, V, Mn, Ni.

The group of Japanese patents, such as e.g. JP60137434, JP62250948 or JP2004284857, disclose catalysts containing noble metals such as Pt, Pd, deposited on a pure TiO2 support or coated with zinc and chromium oxides. Also described are catalysts containing metals from the group Ni, Co, Fe, Mn, Mo, Cr, noble metals (Pd, Pt or Rh) and alkali or alkaline earth metals deposited on thermally resistant inorganic supports.

From patents EP2435182, EP1312413 and US6916458 there are also known palladium or platinum-based methanol steam reforming catalysts, forming alloys with Hf, V, Nb, Ta, Ru, Os, Co, Rh, Ir, Ni, B, Al, Ga, In, Ti, C, Si, Ge, Sn, Pb and containing one or more promoters from the group Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Fe, La, Y, Zr or Pd-ZnO-Cr systems containing at least one metal from the Cr, Ga, Cu, In, Bi, Pt group.

Palladium-zinc catalysts known from patents and scientific literature are obtained by the impregnation method by depositing soluble palladium compounds on a zinc oxide carrier, optionally modified with other metals. Methanol steam reforming reactions with the use of this type of catalysts run with a CO selectivity above 2%.

The aim of the invention was to develop a method for the preparation of a catalyst applicable in the steam reforming reaction of methanol, which, as a product obtained in this way, would make it possible to obtain hydrogen in the highest possible yield and at the same time with the lowest possible content of carbon monoxide.

The method of obtaining a methanol steam reforming catalyst with a support in the form of zinc and chromium oxides with a chromium content of 5-17% by weight, impregnated with palladium and zinc salts, according to the invention, is characterized in that the dried support is mixed at a temperature of 20- 40 ° C for 2-3 hours with an excess of alkaline or neutral impregnating solution, in the form of near saturation of solutions of palladium and zinc compounds, with the exception of halogen salts, preferably, anhydrous solutions of zinc acetylacetonate and palladium acetylacetonate dissolved in acetone, the percentage of which is the palladium ion content is greater than 3 wt.%. per weight unit of the carrier, and the molar concentration of zinc ions in relation to the molar concentration of palladium ions corresponding to the palladium salt used is greater than 2 to 4 times, then the solvent is evaporated at a temperature close to its boiling point, while maintaining the pressure above the solution suitable for the boiling point. The thus obtained wet, solid catalyst is conditioned for 12-6 hours. at the temperature of 20-35 ° C, dried at the temperature of 70-140 ° C for 12-6 hours and calcined to decompose the zinc and palladium compounds used for impregnation with the formation of oxides of these metals, for 0.5-2 hours. at a temperature of 200-400 ° C, preferably for 1 hour. at 250 ° C.

The obtained oxide form of the catalyst is activated with a known gas with reducing properties, e.g. hydrogen or its gaseous mixture, to form active centers in the form of metallic palladium or palladium-zinc alloy for 15 to 0.5 hours at a temperature of 200 -400 ° C, preferably for 1 hour. at 350 ° C.

The invention is illustrated in the following examples.

Example 1 g of a dry carrier in the form of zinc and chromium oxides with a chromium content of 4.98 ± 0.24% by weight was stirred at 20 ° C for 2.5 hours. from 100 ml of an impregnating solution containing 0.1432 g of palladium acetylacetonate anhydrides and 0.2477 g of zinc acetylacetonate dissolved in acetone, then the solvent was evaporated at 20 ° C and a pressure over a solution of 230 mbar to obtain a wet solid. The separated catalyst was conditioned for 12 hours. at 20 ° C and dried at 140 ° C for 6 hours, then calcined for 2 hours at 250 ° C. The obtained oxide form of the catalyst was activated with hydrogen at 400 ° C for 0.5 h, and then its physicochemical properties were tested as described in Example 4.

Example 2 g of a dry carrier in the form of zinc and chromium oxides with a chromium content of 17.20 ± 0.80% by weight, was stirred at 30 ° C for 3 hours. from 100 ml of an impregnating solution containing 0.1432 g of palladium acetylacetonate anhydrides and 0.3716 g of zinc acetylacetonate dissolved in acetone, then the solvent was evaporated at 56 ° C and pressure over 1000 mbar solution to obtain a wet solid. The separated catalyst was conditioned for 6 hours. in tem

PL 234 050 Β1 at 35 ° C and dried at 70 ° C for 12 hours, then calcined for 0.5 hours at 400 ° C. The obtained oxide form of the catalyst was activated with a mixture of methanol and steam at 200 ° C for 15 hours, and then its physicochemical properties were tested as described in Example 4.

Example 3 g of a dry carrier in the form of zinc and chromium oxides, with a chromium content of 9.13 ± 0.37% by weight, was mixed at 40 ° C for 2 hours. from 100 ml of an impregnating solution containing 0.1432 g of palladium acetylacetonate anhydrides and 0.4955 g of zinc acetylacetonate dissolved in acetone, then the solvent was evaporated at 40 ° C and a pressure over a solution of 540 mbar to obtain a wet solid. The separated catalyst was conditioned for 12 hours. at 20 ° C and dried at 110 ° C for 12 hours, then calcined for 1 hour at 250 ° C. The obtained oxide form of the catalyst was activated with hydrogen at 350 ° C for 1 hour, and then its physicochemical properties were tested as described in Example 4.

Example 4

The catalysts obtained by the methods according to the invention were tested and their physicochemical properties were compared with the catalysts known in the art. The individual catalyst numbers correspond to the different Cr content in the catalyst support, determined by XRF fluorescence using an Axios ^mAX spectrometer (PANalytical). The crystallite size of the active phase was tested by hydrogen chemisorption at 110 ° C in the ASAP 2020HD analyzer (Micromeritics).

The results are shown in Tables 1 and 2.

Table 1

Characteristics of the catalysts according to the invention impregnated with anhydrous solutions of palladium acetylacetonate and zinc acetylacetonate, in which the content of palladium ions is 5 wt.%. and the ratio of zinc ions to palladium is 3: 1.

Catalyst Chromium content, (carrier)% wt. Palladium content (active centers) wt.% Crystallite size of the active phase (nm) 1 4.9810.24 4.7410.14 6.63 2 9.1310.37 4.8410.14 5.75 3 10.90-0.44 4.7210.14 6.22 4 17,2010.80 4.8710.15 5.22

Table 2

Characteristics of prior art catalysts impregnated only with anhydrous palladium acetylacetonate solution, in which the palladium ion content is 5 wt.%.

Catalyst Chromium content, (carrier)% wt. Palladium content (active centers) wt.% Crystallite size of the active phase (nm) 1 4.98 ± 0.24 4.6610.14 4.22 2 9.1310.37 4.7310.14 4.65 3 10.90 ± 0.44 4.62 ± 0.14 4.09 4 17,2010.80 4.9010.15 4.41

The data in Tables 1 and 2 show that the catalysts obtained according to the invention have larger crystallites of the active phase containing active centers, which has a significant influence on the more favorable effects of the methanol steam reforming process, as demonstrated in the example 5 below.

PL 234 050 Β1

Example 5

Influence of catalysts according to the invention on methanol conversion and selectivity of methanol steam reforming reaction.

The methanol steam reforming reaction was carried out in the presence of catalysts obtained according to the invention and prior art catalysts - impregnated only with a palladium compound, in a Microactivity Reference (PID ENG & TECH) reference reactor system. In a fixed bed reactor of 0.1 g of catalyst at atmospheric pressure, the catalysts were placed in the form of grains with a size of 0.15-0.3 mm, pre-activated in a hydrogen stream at 350 ° C for 1 hour. A stream of methanol and water vapor, produced by evaporating the metering solution with an HPLC pump, was stirred with a stream of nitrogen. The flow rate of the methanol + water vapor mixture in the molar ratio CH3OH / H2O = 1 / 1.5 was 50 cm ³ / min, and the nitrogen flow rate was 50 cm ³ / min. The loading of the catalyst with a mixture of methanol vapors and water was 30 L / h. giot., and the catalyst loading with a mixture of both vapors and nitrogen was 60 L / h. git. Methanol steam reforming products were analyzed on-line using a Varian GC-450 and Miero GC CP-4900 gas chromatograph system equipped with TCD detectors.

Tables 3-6 show the% conversion of methanol and the selectivity to hydrogen and carbon oxides in the reactions using the individual catalysts.

Table 3

The effects of methanol steam reforming at the temperature of 220 ° C on the catalysts obtained according to the invention by impregnating the support in the form of zinc and chromium oxides with the content of Cr in the support as in Table 1 with a solution containing zinc and palladium in a Zn / Pd ratio of 3: 1.

Γ Catalyst Methanol conversion (Χμλη) and selectivity (S), in% Xweon Sh2 Sc02 Sco 1 14.16 99.52 98.56 1.44 2 11.48 99.62 98.86 1.14 3 12.51 99.64 98.93 1.07 4 11.82 99.72 99.15 0.85

Table 4

The effects of methanol steam reforming at a temperature of 220 ° C with the participation of known supported catalysts in the form of zinc and chromium oxides with Cr content as in Table 2, impregnated only with a palladium compound.

Catalyst Methanol conversion (Xm = oh) and selectivity (S), in% XMeOH ScO2 Sco 1 13.65 99.17 97.52 2.48 2 10.66 99.32 97.95 2.05 3 12.85 99.33 97.99 2.01 4 9.76 99.53 98.58 1.42

The data in Tables 3 and 4 show that the catalysts obtained according to the invention have a significant impact on the more favorable effects of the methanol steam reforming process, and in particular, on the reduction of the selectivity of carbon monoxide formation and its lower content in the produced hydrogen-containing gas, compared to the effects of the steam reforming process. methanol, using known catalysts, obtained by impregnating the same support only with a solution of a palladium compound.

PL 234 050 Β1

Table 5 Effects of methanol steam reforming at 220 ° C on catalysts according to the invention, obtained by impregnating a support in the form of zinc and chromium oxides (9.13% by weight of chromium) with a solution containing zinc and palladium at various molar Zn / Pd ratios.

Zn / Pd molar ratio in the rr used for impregnation Methanol conversion (Χμ «οη) and selectivity (S), in% Xm «oh s »2 $ CO2 Sco 1: 1 9.76 98.33 97.45 2.55 2: 1 10.22 99.67 98.78 1.22 3: 1 11.48 99.62 98.86 1.14 4: 1 11.02 99.72 98.90 1.10 5: 1 8.54 99.59 98.78 1.22

The results presented in Table 5 show that higher methanol conversion rates with a simultaneous reduction in the selectivity of the formation of unfavorable carbon monoxide are achieved when the Zn / Pd molar ratio in the solution used to impregnate the carrier is between 2 and 4.

Table 6

The effects of methanol steam reforming at 220 ° C on the catalysts according to the invention, with different contents of palladium and zinc, while maintaining the Zn / Pd ratio of 3: 1, on a support in the form of zinc and chromium oxides (17.20% by weight of chromium).

Palladium catalyst, wt.% Methanol conversion (Xmcoh) and selectivity (S),% Xmcoh Sh2 ScO2 Sco 1.41 ± 0.08 6.22 98.00 93.99 6.01 2.95 ± 0.09 8.50 98.08 94.24 5.76 4.87 ± 0.15 11.82 99.72 99.15 0.85 7.88 ± 0.22 12.18 99.65 99.50 0.77

The results, presented in Table 6, prove that the palladium content of the catalyst according to the invention greater than 3 wt.% Advantageously increases the methanol conversion and preferably the conversion reduces the selectivity of carbon monoxide formation.

PL 234 050 B1

Claims (3)

Patent claims 1. The method of obtaining a methanol steam reforming catalyst with a support in the form of zinc and chromium oxides with a chromium content of 5-17%, with the participation of palladium and zinc salts, characterized in that the dried support is mixed at a temperature of 20-40 ° C for 2-3 hours with alkaline or neutral impregnating solution, used in excess, in the form of near saturation of solutions of palladium and zinc compounds, except for halogen salts, in which the percentage of palladium ions is greater than 3% by weight, based on the weight unit of the carrier , and the molar concentration of zinc ions in relation to the molar concentration corresponding to the palladium salt used is greater than 2 to 4 times, then the solvent is evaporated at a temperature close to its boiling point, keeping the pressure above the solution appropriate to the boiling point, and the resulting wet catalyst with a constant form, it is conditioned for 12-6 hours. at a temperature of 20-35 ° C, dried at a temperature of 70-140 ° C for 12-6 hours and calcined at the time and temperature required for the decomposition of the zinc and palladium compounds used for impregnation, until the formation of oxides of these metals, and then the obtained oxide form The catalyst is pre-activated with known gases with reducing properties to form active sites in the form of metallic palladium or palladium-zinc alloy. 2. The method according to p. The process of claim 1, wherein the impregnation is preferably made of anhydrous solutions of zinc acetylacetonate, and palladium acetylacetonate dissolved in acetone. 3. The method according to p. The method of claim 1, characterized in that the calcination of the catalyst is carried out at a temperature of 200-400 ° and during 0.5-2 hours, preferably for 1 hour. at 250 ° C (and its activation within 15 to 0.5 hours, at 200-400 ° C, preferably within 1 hour at 350 ° C.