Catalyst copper/zirconia

The above example illustrates how important the knowledge of the solid-state reactions and segregational phenomena is for successful preparation of efficient catalysts from glassy precursors. The occurrence of the copper segregation upon hydrogen exposure at elevated temperature was found to be crucial for successful preparation of copper/zirconia catalysts from Cu-Zr precursors this segregation depends on various factors such as the structure of the precursor material, the oxygen content, and the chemical composition of the alloy. 

For illustration, we may consider the preparation of a palladium/zirconia catalyst highly active for the oxidation of CO [4.47,71], the preparation of a copper/zirconia catalyst for the hydrogenation of C02 [4.23], and the preparation of iron/zirconia for ammonia synthesis [4.44]. 

EFFECT OF PREPARATION VARIABLES ON CATALYTIC BEHAVIOUR OF COPPER/ZIRCONIA CATALYSTS FOR THE SYNTHESIS OF METHANOL FROM CARBON DIOXIDE... 

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. 

The crystallization of the amorphous zirconia is likely to result in a drastic decrease of the copper/zirconia interfacial area which certainly contributes to the loss of activity observed upon crystallization. Our investigations provide further support for the crucial role of the interfacial area in copper/zirconia catalysts. Further work focusing on the structural and chemical properties of this interphase and its role in methanol synthesis is presently undertaken. 

Centi, G., Cerrato, G., D Angelo, S. et al. (1996) Catalytic behavior and nature of active sites in copper-on-zirconia catalysts for the decomposition of N20, Catal. Today 27, 265. 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

Raudaskoski R, et al. Catalytic activation of CO2 use of secondary CO2 for the production of synthesis gas and for methanol synthesis over copper-based zirconia-containing catalysts. Catal Today. 2009 144(3 4) 318-23. 

Many catalytic formulation are proposed for the hydroconversion of CO2, most of them are based on promoted copper-zinc oxides given by the long industrial experience on methanol synthesis from syngas (CO+CO2+H2) [3-6]. Specific methanol catalysts working for CO2 are proposed including promoted Cu-Zn catalysts [3,6], zirconia supported systems [7] as well as copper associated with stabilized rare earth oxides [8,9]. In the last case Cu-LaZr and CuZn-Lcfer catalysts were proposed and showed interesting catalytic properties in the methanol formation. 

Bergamaschi, V.S., Carvalho, F.M.S., Rodrigues, G, and Fernandes, D.B. Preparation and evaluation of zirconia microspheres as inorganic exchanger in adsorption of copper and nickel ions and as catalyst in hydrogen production from bioethanol. Chemical Engineering Journal, 2005, 112 (1-3), 153. 

Recently, the high activity of a Cu-on-Zr02 catalyst in steam reforming of methanol has been interpreted as an interaction between copper and zirconia (133). A similar interaction might also contribute to the activity of the foregoing catalyst formed from the amorphous alloy. 

This new single-step synthesis unites the simplicity of preparation and lower production costs, with the outstanding properties of the final catalysts. By the single-step procedure proposed here, deposition of dispersed nanoparticles of noble metals on ceramic supports with customised textural properties and shape was achieved. Noble metals including platinum, palladium, rhodium, ruthenium, iridium, etc. and metal oxides including copper, iron, nickel, chromimn, cerium oxides, etc on sepiolite or its mixtures with alumina, titania, zirconia or other refractory oxides have been also studied. 

Our study also showed that the catalyst deactivates with time-on-stream even at low conversions. The activity dropped 30% from its initial value over a few hours. The present work further investigates this deactivation phenomenon in order to evaluate more thoroughly the potential application of copper oxide catalysts for OMR. Experiments were conducted to determine the cause of deactivation and the effect of the support on deactivation rate. Zirconia has been explored as an alternative support to ZnO and/or alumina. Reaction and deactivation rate data for 18-hour OMR reactions are reported for these catalysts. 

Lindstrom et al. [55] developed a fixed-bed autothermal methanol reformer designed for a 5 kW fuel cell operated with copper/zinc oxide catalyst doped with zirconia. The system was started without preheating from ambient temperature by methanol combustion in a start-up burner, which was operated at sixfold air surplus to avoid excessive temperature excursions. Because significant selectivity toward carbon monoxide was observed for the autothermal reforming process, a WGS stage became mandatory [55]. 

Lattner and Harold [56] performed autothermal reforming of methanol in a relatively big fixed-bed reactor carrying 380 g BASF alumina-supported copper/zinc oxide catalyst modified with zirconia. The 01C ratio was set to 0.22 while the SIC ratio varied from 0.8 to 1.5. The axial temperature profile of the reactor, which had a length of 50 cm, was rather flat, the hot spot temperature did not exceed 280° C which was achieved by the air distribution system through porous ceramic membrane tubes. More than 95% conversion was achieved. Very low carbon dioxide formation was observed for this reactor only 0.4 vol.% was found in the reformate. However, the WHSV calculated from the data of Lattner and Harold [56] reveals a low value of only 6 l/(h gcat) for the highest CHSV of 10 000 h reported. 

Partial oxidation of methanol is less frequently reported in the open literature. Cubeiro et al. investigated the performance of palladium/zinc oxide, palladium/ zirconia and copper/zinc oxide catalysts for partial oxidation of methanol in the temperature range between 230 and 270 °C (194j. Increasing selectivity towards hydrogen and carbon dioxide was achieved with increasing conversion, while selectivity towards steam and carbon monoxide decreased. The palladium/zinc oxide catalyst showed lower selectivity towards carbon monoxide compared with the palladium/zirconia catalyst. However, the lowest carbon monoxide selectivity was determined for the copper/zinc oxide catalyst. 

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