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Acetylene trimerizes to benzene on the (111) face of copper, as it does on the (100) and (110) planes. However, Cu(111) also yields butadiene and cyclooctatetraene, the latter never previously found with Cu or any other material. No coverage threshold is observed for the onset of these coupling reactions, implying high adsorbate mobility: gaseous benzene is formed by a surface reaction rate-limited process, whereas butadiene and cyclooctatetraene are formed by desorption rate-limited processes. H/D isotope tracing shows that benzene formation proceeds via a statistically random associative mechanism, whereas butadiene formation is associated with strong kinetic isotope effects, probably associated with C-H cleavage. A pericyclic mechanism involving dimerization of C4H4 metallocycles is proposed to account for the formation of cyclooctatetraene. We also found that approximately 45 nm alpha-alumina supported copper particles operated under catalytic conditions at atmospheric pressure yield the same principal reaction products as those found with Cu(111) under vacuum conditions. It therefore seems likely that the elementary reaction steps that describe the surface chemistry of the model system are also important under practical conditions. Comparison of the structure, bonding, and reactivity of acetylene on Cu(111) and Pd(111) indicates that the effectiveness of copper in promoting C-H cleavage in adsorbed acetylene is associated with greater rehybridization of the C-C bond with concomitant weakening of the C-H bond.

This paper describes the development of a novel proximity gauging technique for soft deposits, exploiting a siphon effect. This non‐contact technique has the capability to measure the thickness of soft deposits on a surface in situ and in real time. A theoretical model of performance has been developed and its validity demonstrated by calibration experiments. Local thickness measurements of soft deposits such as whey protein deposit, supermarket butter and sticky foam on metal surfaces had an accuracy of ±20 μm for a deposit thickness of 500 to 1000 μm. The potential of this technique for on‐line monitoring of fouling and cleaning processes in liquid environments is demonstrated by preliminary studies of alkali (NaOH) cleaning of whey protein deposits from stainless steel surfaces.

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