Cu-Zn hydroxycarbonates have been studied as precursors of Cu-ZnO catalysts, with particular reference to the effect on catalyst activity of ageing the precursor prior to decomposition and reduction. The precursor obtained by precipitation from mixed nitrate solution ( C u / Z n molar ratio 2 : 1 ) at 333 K and pH 7.0 consisted of zincian malachite ( C u / Z n = 8.5: 1.5) and aurichalcite. The precursor was aged in the mother liquor at 333 K for various times. Characterisation by XRD, i.r., DTA, electron microscopy, EDAX and XPS showed that ageing led to loss of the aurichalcite and production of a more finely divided copper-enriched ( C u / Z n = 2 : 1) malachite phase. The unaged precursor yielded a catalyst of low activity for both methanol synthesis (studied at 50 bar and at 1 bar) and the reverse water-gas shift reaction. The aged precursor gave catalysts of much higher activity for both reactions. Increased ageing did not change the selectivity ratio for methanol synthesis cs. reverse shift in the CO,+ H, reaction at normal pressure.
The hydrogen sulfide absorption capacity of zinc oxide doped with first-row transition-metal oxides (ca. 5% metal oxide loading) has been determined using a pulse reactor. The doped oxides were prepared either by impregnation of ZnO with t h e transition-metal nitrates or by coprecipitation of t h e transition-metal and zinc nitrates with ammonium/sodium carbonate. These absorbent precursors were then calcined to give the mixed oxides.Transmission electron microscopy studies of t h e impregnated and calcined absorbents revealed that the transition-metal oxides were finely dispersed over the ZnO a s y-Fe203, Co,O, and CuO from the respective nitrate salts of these metals. The basal planes were t h e predominant exposed faces of the hexagonal ZnO in all t h e absorbents, irrespective of whether t h e y were prepared by t h e coprecipitation or impregnation route. CuO and Co,O, were not seen as separate phases in the respective calcined coprecipitated absorbents, but t h e particle morphology was noticeably changed after sulfidation and crystalline ZnS was detected by electron diffraction. Oxides prepared by t h e coprecipitation route had higher surface areas and a greater capacity for H,S removal than their impregnated counterparts. Doping with iron salts had little effect on t h e H2S uptake of ZnO, irrespective of whether an impregnation or a coprecipitation route had been used, but doping with copper or cobalt salts resulted in a marked enhancement in t h e H,S uptake in each case.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.