Methanol synthesis catalyst preparation

When methanol synthesis catalyst, prepared from CuO, ZnO and CrOj, was mixed with HY zeolite, C2+ hydrocarbons were obtained in a good selectivity(Run 1)[2]. The same catalyst made into granule gave better results (Run 3). The selectivities to ethane, propane and butane were higher and that to methane was lower. No olefin was observed. The hydrocarbons distribution of typical Cu-Zn-Cr/HY is shown in Figure 1. This is a typical distribution of MTG reaction, and quite different from Schultz-Anderson-Flory law. 

Several series of methanol synthesis catalysts were prepared by the coprecipitation of the appropriate metal salts in either Na2C03 or (NH4)2C03 using the CaviPro 300 (dual-orifice processor) at both high and low pressures. The experiments were carried out using a 0.152-mm first orifice while varying... 

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. 

In an NMR investigation of a methanol synthesis catalyst based on Cu/Zn/Al oxides (95), a resonance line was found at 85 ppm (with respect to H2O) and attributed to dissociativcly adsorbed hydrogen on copper metal. Its intensity was found to be highly variable, even for similar sample preparations and treatments. The hypothesis was therefore proposed that the actual availability of copper metal in these systems is very sensitive to preparation and handling details, e.g., oxygen contamination. 

Cu-Zn-Cr oxides were prepared as follows. CuO was added to an aqueous solution of CrOj, and ZnO was added after 1 h aging. The obtained paste was dried without heating. Fe-based catalysts were prepared by the coprecipitation of the corresponding nitrates using sodium hydroxide. The precipitate was washed five times, dried at 120 C for 6 h and calcined at SSO C for 3 h. The composite catalysts were obtained by the physical mixing of the equal amounts of a methanol synthesis catalyst and a zeolite. HY [JRC-Z-HY4.8(2)] and NaY(JRC-Z-Y4.8) were provided from the Catalysis Society of Japan as the Reference Catalyst. 

The yield of hydrocarbons (14.4%) were higher than that of equilibrium conversion of COj to methanol (ca 7% at 4001C, 50 atm). It means that methanol formation was accelerated by MTG reaction. When methanol synthesis catalyst was prepared by coprecipitation, the yield of hydrocarbons decreased (Run 2). This seems to be due to the deactivation of zeolite by the sodium remaining after 5 times wash. Similar tendency was observed on the hydrocarbon synthesis between two Cu-Zn/HY composite catalyst, in which one Cu-Zn catalyst was precipitated by Na2C03, and another Cu-Zn catalyst was precipitated by oxalic acid[3]. When methanol synthesis catalyst was prepared by sodium compound, remaining sodium deactivate an active site of zeolite on MTG reaction. 

The catalytic CO hydrogenation activity for methanol production over Cu based catalysts are listed in Table 2. In Table 2, the activity of conventional copper based methanol synthesis catalysts, Cu/Zn0/Cr203 (Cu Zn Cr = 6 3 1) and Cu/Zn0/Al203 (Cu Zn AI = 4 5 1), as well as Cu-Yb203 prepared in the present work at various reaction... 

It is known that ZnO alone is a methanol synthesis catalyst [8,9,10], however, the impurities (for example, alkaline residues) introduced to the catalyst during the preparation accelerate side reactions including higher alcohol synthesis and hydrocarbon synthesis [9], In this paper, the support and the gold catalysts were prepared in a similar way, which enables us to investigate the function of gold over the supported catalysts. The results above show that the catalytic behaviour is improved with the addition of Au to the catalyst, since the Au/ZnO selectivity produces alcohols as products and there is a distinct increase in the selectivity for higher alcohols for Au/ZnO when compared with ZnO alone. 

Wu ZG. Copper-based methanol synthesis catalyst to enlarge the pilot prepared by acid — base alternately deposition. Dissertation,. Hangzhou Zhejiang University of... 

A series of copper-zirconia catalysts have been prepared by methods of sequential precipitation, coprecipitation and deposition precipitation. The influence of various pretreatments and of the copper zirconia ratio on the structural and chemical properties of these samples are examined. High activity and selectivity of the catalysts is shown to be correlated to the presence of amorphous zirconia which is stabilized by copper ions. The results indicate that the structural and chemical properties of the support and particularly the interface copper/zirconia are most decisive in governing the catalytic properties of these methanol synthesis catalysts. 

Although methanol synthesis catalysts have been studied intensively for several years there is still much controversy about the nature of the active components and the reaction steps that take place on them. Many aspects of the reaction mechanism are still not fully understood and are the subject of an active debate. Several investigations (refs. 10,11) have shown that over typical commercial catalysts practically all of the methanol is formed from COj under industrial conditions and that support effects are minimal for these catalysts (ref. 12). Other workers reported a marked support effect for the synthesis of methanol over copper catalysts prepared by different methods (refs. 3,7,8,13) showing that the activity of supported copper catalysts depends strongly on both the choice of the support and the nature of the feedstock. The results suggest that more than one mechanism may lead to methanol. 

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. 

Along with hydrophobicity, large amounts of both water (to promote hydrolysis) and methanol employed as co-solvent in the catalyst preparation (to promote homogeneity) are needed to ensure optimal reactivity, showing the number of experimental parameters of the sol-gel synthesis which can be controlled independently to optimize the performance of the resulting catalyst. Finally, in contrast to zeolites and other crystalline porous materials, amorphous sol-gel materials show a distribution of porosity which does not restrict the scope of application of sol gel catalysts to substrates under a threshold molecular size. 

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