Oxidation over Copper, Silver and Gold Catalysts

Oxidation over Copper, Silver and Gold Catalysts 

Copper and silver have been in use as industrial catalysts for selective oxidation reactions since the early years of this century. Although there have subsequently been many scientific investigations of these processes, a number of problems still remain. This review is intended to cover the most significant areas of published work in this field from 1972 to 1978. Gold has not been used commercially as an oxidation catalyst but has been included where relevant studies have been made. 

Since the area under review is large, we have not tried to cover catalysis by alloys or mixed oxides, neither have we attempted to review the extensive patent literature. Passing references have been made to industrial processes using copper and silver catalysts, but emphasis has been placed primarily on the scientific, and particularly the mechanistic, aspects of the systems involved. We have not hesitated to include non-catalytic work when we felt it contributed to the understanding of a particular catalytic phenomenon. 

Partial oxidation over copper and silver has been reviewed by Voge and Adams and more recently by Hucknel. Adsorption and catalysis on alloys containing copper, silver, and gold has been covered by Moss and Whalley.  

2 Interaction of Oxygen with Copper, Silver, and Gold 

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The results of the oxidation of C2—C5 olefins over copper(i) oxide, silver, and gold catalysts are summarized in Table 1. We have excluded data from studies where additives have been deliberately included in the catalyst, or process gas stream, in order to improve the performance. Where several studies have been carried out we have quoted the best selectively obtained. While copper(i) oxide and gold give unsaturated aldehydes as the major product of partial oxidation, silver gives the epoxide. Copperfii) oxide is not a selective catalyst for olefin oxidation. The difference in behaviour between copper(i) and copper(ii) oxides is in line with the general trend in oxide catalysis. The selective catalysts tend to be those with either a full or an empty tZ-shell, i.e. the oxides of Groups IVA, VA, and VIA, and IB, IIB, IVB, VB, and VIB. ... 

Compensation trends found for decomposition of formic acid on metal (and other) catalysts are represented diagrammatically in Fig. 7. Line I (Table III, Q) refers to reactions over nickel and copper (3, 190, 194, 236), gold (5,189,237), cobalt (137,194), and iron (194) the observations included in this group were obtained by selection, since other metals, which showed large deviations, were omitted [see also (5), p. 422], Line I is close to that calculated for the reaction catalyzed by nickel metal (Table III, R) (3, 137, 189-194, 238). Lines II (19,233) and III (3, 234, 235) (Table III, O and P) refer to decomposition on silver. The other lines were found for the same rate process on IV, copper-nickel alloys (190) V, oxides (47, 137), VI, tungsten bronzes (239) and VII, Cu3Au (Table III, S) (240a). 

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