Diane Stirling

Bio: Diane Stirling is an academic researcher from University of Bath. The author has contributed to research in topics: Catalysis & Zinc. The author has an hindex of 3, co-authored 4 publications receiving 123 citations.

Copper–zinc oxide catalysts. Activity in relation to precursor structure and morphology

Abstract: 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 (Cu/Zn molar ratio 2:1) at 333 K and pH 7.0 consisted of zincian malachite (Cu/Zn ≈ 85:15) 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 (Cu/Zn = 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 vs. reverse shift in the CO2+ H2 reaction at normal pressure.

Catalytic Activity of Reduced CuxZn(1-x)O and CuO/CuxZn(1-x)O in CO2/H2 Reactions

Abstract: Monophasic CuO-ZnO solid solution (Cu x Zn 1-x O) has been prepared at high temperature and superficially reduced at 560 K to produce a catalyst for the CO 2 /H 2 reactions of methanol synthesis and reverse water-gas shift. The activity in both reactions is markedly superior to that of catalysts derived from biphasic systems containing additional CuO, i.e. CuO/Cu x Zn 1-x O. The enhanced activity in the former case is ascribed to very finely-divided Cu particles present in intimate contact with the zinc oxide matrix.

Tandem amine and ruthenium-catalyzed hydrogenation of CO2 to methanol.

Abstract: This Communication describes the hydrogenation of carbon dioxide to methanol via tandem catalysis with dimethylamine and a homogeneous ruthenium complex. Unlike previous examples with homogeneous catalysts, this CO2-to-CH3OH process proceeds under basic reaction conditions. The dimethylamine is proposed to play a dual role in this system. It reacts directly with CO2 to produce dimethylammonium dimethylcarbamate, and it also intercepts the intermediate formic acid to generate dimethylformamide. With the appropriate selection of catalyst and reaction conditions, >95% conversion of CO2 was achieved to form a mixture of CH3OH and dimethylformamide.

The role of zinc oxide in Cu/ZnO catalysts for methanol synthesis and the water–gas shift reaction

Abstract: All commercial catalysts for methanol synthesis and for the water–gas shift reaction in the low temperature region contain zinc oxide in addition to the main active component, copper. The varied benefits of zinc oxide are analysed here. The formation of zincian malachite and other copper/zinc hydroxy carbonates is essential in the production of small, stable copper crystallites in the final catalyst. Further, the regular distribution of copper crystallites on the zinc oxide phase ensures long catalyst life. Zinc oxide also increases catalyst life in the water–gas shift process by absorbing sulphur poisons but it is not effective against chloride poisons. In methanol synthesis, zinc oxide (as a base) removes acidic sites on the alumina phase which would otherwise convert methanol to dimethyl ether. Although bulk reduction of zinc oxide to metallic zinc does not take place, reduction to copper–zinc alloy (brass) can occur, sometimes as a surface phase only. A new interpretation of conflicting measurements of adsorbed oxygen on the copper surfaces of methanol synthesis catalysts is based on the formation of Cu–O–Zn sites, in addition to oxygen adsorbed on copper alone. The possible role of zinc oxide as well as copper in the mechanisms of methanol synthesis is still the subject of controversy. It is proposed that, only under conditions of deficiency of adsorbed hydrogen on the copper phase, hydrogen dissociation on zinc oxide, followed by hydrogen spillover to copper, is significant.

Performance Improvement of Nanocatalysts by Promoter-Induced Defects in the Support Material: Methanol Synthesis over Cu/ZnO:Al

Abstract: Addition of small amounts of promoters to solid catalysts can cause pronounced improvement in the catalytic properties. For the complex catalysts employed in industrial processes, the fate and mode of operation of promoters is often not well understood, which hinders a more rational optimization of these important materials. Herein we show for the example of the industrial Cu/ZnO/Al2O3 catalyst for methanol synthesis how structure–performance relationships can deliver such insights and shed light on the role of the Al promoter in this system. We were able to discriminate a structural effect and an electronic promoting effect, identify the relevant Al species as a dopant in ZnO, and determine the optimal Al content of improved Cu/ZnO:Al catalysts. By analogy to Ga- and Cr-promoted samples, we conclude that there is a general effect of promoter-induced defects in ZnO on the metal–support interactions and propose the relevance of this promotion mechanism for other metal/oxide catalysts also.