Structural behaviour of copper chloride catalysts during the chlorination of CO to phosgene

Abstract

The interaction of CO with an attapulgite-supported Cu(II)Cl₂ catalyst has been examined in a micro-reactor arrangement. CO exposure to the dried, as-received catalyst at elevated temperatures leads to the formation of CO₂ as the only identifiable product. However, phosgene production can be induced by using a catalyst pre-treatment where the supported Cu(II)Cl₂ sample is exposed to a diluted stream of chlorine. Subsequent CO exposure at ∼370 °C then leads to phosgene production. In order to investigate the origins of this atypical set of reaction characteristics, a series of X-ray absorption experiments were performed that were supplemented by DFT calculations. XANES measurements establish that at the elevated temperatures connected with phosgene formation, the catalyst is comprised of Cu⁺ and a small amount of Cu²⁺. Moreover, the data show that unique to the chlorine pre-treated sample, CO exposure at elevated temperature results in a short-lived oxidation of the copper. On the basis of calculated CO adsorption energies, DFT calculations indicate that a mixed Cu⁺/Cu²⁺ catalyst is required to support CO chemisorption.