Copper zinc-based catalysts

According to the reaction temperature (Chen et al, 2008), the WGSR falls into two categories high-temperature shift catalyst (HTC) and low-temperature shift catalyst (LTC). The catalyst commonly used in the former is an iron-chromium-based catalyst, whereas a copper-zinc-based catalyst is frequently adopted in the latter. 

Current WGS catalysts suffer from the facT that they are mostly pyrophoric and thus require a defined shutdown cycle to prevent ignition. In addition to that, the copper-zinc-based catalyst also requires reduction prior to use. So the SILP catalysts were tested for their restart behavior and tolerance against condensation. Both rapid shutdown and fast restart are required for hydrogen generation scenarios, but one... 

Aside from the recently described Cu/Th02 catalysts, copper on chromia and copper on silica have been reported to catalyze methanol synthesis at low temperatures and pressures in various communications that are neither patents nor refereed publications. It is not feasible to critically review statements unsupported by published data or verifiable examples. However, physical and chemical interactions similar to those documented in the copper-zinc oxide catalysts are possible in several copper-metal oxide systems and the active form of copper may be stabilized by oxides of zinc, thorium, chromium, silicon, and many other elements. At the same time it is doubtful that more active and selective binary copper-based catalysts than... 

Methanation as final purification for the raw gas from partial oxidation was proposed by Topsoe [739]. In this case the shift conversion is carried out in two stages with a special sulfur-tolerant shift catalyst followed by removal of hydrogen sulfide and carbon dioxide in an acid gas removal unit. Because of the potential danger of a sulfur break-through causing poisoning, the normal copper - zinc - alumina catalyst is usually not applied, which is surprising as the same risk exists in partial oxidation based methanol plants for the similarly composed methanol catalyst. 

Nissui-Topsoe Methanol-Synthesis Process. A schematic flow diagram [29] of the process offered by Haldor Topsoe of Denmark and Nihon Suiso Kogyo Company of Japan is given in Figure 3.17. The process is based on a copper-zinc-chrome catalyst that is active at 230—280 C and at a pressures of 100-200 atm. 

The conversion of methanol to hydrocarbons is the most studied reaction of oxygenates over microporous solids, for both commercial and academic reasons. Methanol can be generated from syngas over copper- and zinc-based catalysts using the ICI process, and syngas can be prepared from methane, which is a readily available resource. Under the correct economic conditions, methanol conversion reactions can provide an important route to higher... 

Palladium is the precious metal most frequently apphed for methanol steam reforming [176-178]. Despite its higher price compared with the copper-based systems, it is an attractive alternative owing to the potential for higher activity and greater robustness, which are key features for small scale reformers. The combination of palladium and zinc showed superior performance and soon the formation of a palladium-zinc alloy was identified as a critical issue for optimum catalyst performance [179]. Besides palladium/zinc oxide, palladium/ceria/zinc oxide may well be another favourable catalyst formulation [177]. However, precious metal based catalysts have a tendency to show higher carbon monoxide selectivity than copper-zinc oxide catalysts, because it is a primary product of the reforming reaction over precious metals. 

Cobalt catalysts such as cobalt/manganese and cobalt/chromium show higher activity than iron/chromium catalysts at temperatures exceeding 300 °C and are highly sulfur tolerant [107]. However, their activity is certainly lower than that of the precious metal catalysts discussed below. Additionally, they are not suitable for low-temperature applications due to their low activity in this temperature range. Ruettinger et al. reported on proprietary base-metal water-gas shift catalyst development. The catalysts were claimed to have lower pyrophoricity than copper/zinc oxide catalysts, and to be stable towards air exposure at 150 ° C and even to liquid water [302]. 

Precious metal based water-gas shift catalysts have zero reaction order for carbon monoxide below 300 ° C, which means that the rate of conversion is not affected by the carbon monoxide concentration in the low temperature range [57,303]. This is not the situation for the copper/zinc oxide catalysts described above [304]. However, the products carbon dioxide and hydrogen have an inhibiting effect on the reaction in the low temperature range for both types of catalysts [305, 304]. Many publications in the field of water-gas shift catalysts do not take these effects into consideration, which impairs the applicability of the results considerably. Frequently only carbon monoxide and steam are fed to the catalyst samples and the activity is determined while ignoring the effects of product inhibition. 

The reformate left the reformer with a temperature of 814 °C and entered a zinc oxide trap. However, this would he not feasible in a practical system, because zinc oxide adsorbent materials cannot tolerate temperatures exceeding 450 °C. The reformate, which was cooled to 440 °C in heat-exchanger E-2 was then passed to the water-gas shift reactor. This reactor was cooled by steam generation at 15-bar pressure and a temperature of200 °C in a counternoble metal based rhenium/alumina catalyst at the inlet section followed by a copper/zinc oxide catalyst at the outlet section. Despite the fact that a water-gas shift catalyst of fairly low activity had been chosen for the... 

Even the industrial copper/zinc/alumina-based catalysts have been modified to achieve higher productivity or longer catalyst life. ICI recently announced its third-generation copper/zinc/alumina catalyst, described as a "step change" over the previous catalysts [16, 17]. This development was made through optimized formulation and particle and pellet size. Researchers at the University of New South Wales, Australia claimed another new breakthrou on this type of the catalyst [16]. A 100% improvement in performance over the previous catalysts was claimed. 

Isobutyl alcohol [78-83-1] forms a substantial fraction of the butanols produced by higher alcohol synthesis over modified copper—zinc oxide-based catalysts. Conceivably, separation of this alcohol and dehydration affords an alternative route to isobutjiene [115-11 -7] for methyl /-butyl ether [1624-04-4] (MTBE) production. MTBE is a rapidly growing constituent of reformulated gasoline, but its growth is likely to be limited by available suppHes of isobutylene. Thus higher alcohol synthesis provides a process capable of supplying all of the raw materials required for manufacture of this key fuel oxygenate (24) (see Ethers). 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

The low-pressure methanol synthesis process utilizes ternary catalysts based on copper, zinc oxide, and another oxide, such as alumina or chromia, prepared by coprecipitation. Cu-Zn0-Al203 and Cu-Zn0-Cr203 are usually the most important industrial catalysts. A significant advance was made when a two-stage precipitation was suggested in which ZnAl2C>4, a crystalline zinc aluminate spinel, was prepared prior to the main precipitation of copper-zinc species.372 This alteration resulted in an increase in catalyst stability for long-term performance with respect to deactivation. Catalyst lifetimes industrially are typically about 2 years. 

Note added in proof The benzoylation of diols using zinc- and copper-based catalysts has been reported, see Trost BM, Mino T (2003) J Am Chem Soc 125 2410-2411 Matasumura Y, Maki T, Murakami S, Onomura 0 (2003) J Am Chem Soc 125 2052-2053... 

In connection with nickel-catalysed reductive coupling reactions of dihaloarenes, leading to poly(arylene)s, the copper-catalysed reductive carbenoid coupling reactions involving substituted bis(dichloromethyl)arenes and metals or other reductants should be mentioned. The reductive carbenoid coupling of bis(phenyldichloromethyl)arene with zinc in the presence of Cu-based catalysts is shown below ... 

Low-pressure methanol synthesis relies almost exclusively on catalysts based on copper, zinc oxide, and alumina. The catalysts are produced by ICI (now Johnson Matthay), Siidchemie (now Clariant), Haldor Topsoe, in the past also by BASF, and other chemical enterprises and contain 50-70 atomic % CuO, 20%-50% ZnO, and 5%-20% Al203. Instead of alumina, chromium oxide and rare earth oxides have also been used. The mixed oxide catalysts are usually shipped as 4-6 mm cylindrical pellets with specific surface area of 60-100 m2/g. The catalysts are activated in situ with dilute hydrogen, often derived from off-gases from synthesis gas... 

Saito M, et al. Development of copper/zinc oxide-based multicomponent catalysts for methanol synthesis from carbon dioxide and hydrogen. Appl Catal A Gen. 1996 138(2) 311—18. 

The gas from the HTS is cooled to increase the conversion, and then it is passed through the low temperature shift (LTS) converter. The LTS converter is filled with copper oxide/zinc oxide-based catalyst and operates at about 200-220°C. The residual CO content is about 0.2 to 0.4 percent (on a dry gas basis).53... 

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