Methanol-synthesis catalyst precursor

Baltes C, Vukojevic S, Schiith F. Correlations between synthesis, precursor, and catalyst structure and activity of a large set of CuO/ZnO/Al2C>3 catalysts for methanol synthesis. Journal of Catalysis. 2008 258(2) 334-344. 

There has been much work on new catalysts for methanol synthesis however, commercial catalysts have been composed of Cu-Zn0-Al203(Cr203) even at present. In order to obtain the catalyst that has optimum structure of active sites, the most reliable way must be to increase the Cu dispersion and to accomplish the fine interdispersion between Cu and ZnO. It is described that AU is the sole precursor that derives such an active catalyst. For the selective formation of AU, the conditions of precipitation and the characterization of intermediates and precursors and finally the formation mechanism that can explain the distribution of precursors are discussed. 

Muller M, Hermes S, Kaehler K, van den Berg MWE, Muhler M, Fischer RA. Loading of MOF-5 with Cu and ZnO nanoparticles by gas-phase infiltration with organometallic precursors properties of Cu/ZnO MOF-5 as catalyst for methanol synthesis. Chem Mater 2008 20 4576-87. 

Fig. 6.7. Copper-based catalysts for methanol synthesis. A novel device for controlled precipitation enabled separation of blue from green products. Structural analysis (top left) revealed that the blue products are disordered nanocrystalline materials furnishing poor catalysts. The green products are mixtures of two phases, malachite (violet) and auricalcite (red). By systematically optimizing the reaction conditions it was possible to prepare phase-pure green products and thereby to improve thesynthesisofthe working catalyst based on pure malachite precursors. In the X-ray diffraction pattern (top right), the features are labeled by the Miller Indices, indicating the diffraction lattice plane of the crystal °29 is the diffraction angle.

The presence of copper shifts the exothermal crystallization peak to 823 K for sample SI (10 at% Cu) and to 893 K for samples S3-S7 (30-70 at% Cu, Fig. 1). The exothermic peaks at 473 K and 550 K (Fig. Ic) arc associated with the presence of acetate in the precursor, as emerges from a comparison with the DSC curve of the pure nitrate precursor (Fig. If). Calcination at 623 K in air for 3 h results in an acetate free catalyst (Fig. Id). The exothermic signals appearing at 480 and 613 K after exposing this catalyst to methanol synthesis... 

Microanalysis of a Copper-Zinc Oxide Methanol Synthesis Catalyst Precursor... 

Himelfarb, P. B., Simmons, G. W., Klier, K., Herman, R. G., "Precursors of the Copper-Zinc Oxide Methanol Synthesis Catalysts," J. Catal., in press. 

Besides supported (transition) metal catalysts, structure sensitivity can also be observed with bare (oxidic) support materials, too. In 2003, Hinrichsen et al. [39] investigated methanol synthesis at 30 bar and 300 °C over differently prepared zinc oxides, namely by precipitation, coprecipitation with alumina, and thermolysis of zinc siloxide precursor. Particle sizes, as determined by N2 physisorpt-ion and XRD, varied from 261 nm for a commercial material to 7.0 nm for the thermolytically obtained material. Plotting the areal rates against BET surface areas (Figure 3) reveals enhanced activity for the low surface area zinc... 

Another study on the preparation of supported oxides illustrates how SIMS can be used to follow the decomposition of catalyst precursors during calcination. We discuss the formation of zirconium dioxide from zirconium ethoxide on a silica support [15], Zr02 is catalytically active for a number of reactions such as isosynthesis, methanol synthesis, and catalytic cracking, but is also of considerable interest as a barrier against diffusion of catalytically active metals such as rhodium or cobalt into alumina supports at elevated temperatures. 

Unpromoted Cu/Si02 is found to have a low activity for methanol synthesis from H2/CO mixtures, whereas an increased activity from H2/CO2. Alkali metal promotion increases the activity for methanol synthesis from the H2/CO mixtures, probably due to the increase in surface OH groups engaged in the formation of the formate species which are the precursors to the methanol. Cu/Si02 powder catalysts (with 5 wt% Cu) can be prepared by ion exchange of silica with Cu(NOs)2 in aqueous solution, followed by calcination and reduction. Such preparations contain very fine Cu particles ( 0.5 nm) on a powdered silica support as revealed by HRTEM. 

The preparation of Cu/ZnO catalysts and precursors for the methanol synthesis reaction have been described [87, 88], while others [89] used a mixture of Pt, Ru and a leachable metal such as A1 to prepare catalysts for CO-tolerant catalysts for fuel cells. 

Behrens M, et al. Knowledge-based development of a nitrate-free synthesis route for Cu/ ZnO methanol synthesis catalysts via formate precursors. Chem Commun. 2011 47 (6) 1701-3. 

Figure 5.3.7 The variation of CO and methanol production rates with space velocity (A) and methanol synthesis rates on promoted CuZn-based catalysts derived from hydrotalcite and Malachite precursors (B). Reaction conditions 200 mg catalyst, 30 bar, 230°C, 3 1 H2 C02.

Figure 5.3.9 (A) Simplified geometric model [46, 89] for the preparation of industrial Cu/ZnO catalysts comprising subsequent meso- and nanostructuring of the material from [56], In a first micro structure directing step (mesostructuring), the Cu,Zn coprecipitate crystallizes in the form of thin needles of the zincian malachite precursor, (Cu,Zn)2(0H)C03. In a second step, the individual needles are decomposed and demix into CuO and ZnO. The effectiveness of this nanostructuring step depends critically on a high Zn content in the precursor, which in zincian malachite is limited to Cu Zn ca. 70 30 due to solid-state chemical constraints [75]. Finally, interdispersed CuO/ZnO is reduced to yield active Cu/ZnO. (B) Chemical memory Dependence of catalytic activity in methanol synthesis on the conditions of the coprecipitation and aging steps, from [85].

Li JL, Inui T. Characterization of precursors of methanol synthesis catalysts, copper zinc aluminum oxides, precipitated at different pHs and temperatures. Appl Catal A Gen. 1996 137(1) 105 17. 

Shen GC, Fujita SI, Takezawa N. Preparation of precursors for the Cu/ZnO methanol synthesis catalysts by coprecipitation methods - effects of the preparation conditions upon the structures of the precursors. J Catal. 1992 138(2) 754—8. 

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