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

Abstract

The interaction of CO with an attapulgite-supported Cu(II)Cl 2 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 CO 2 as the only identifiable product.However, phosgene production can be induced by using a catalyst pre-treatment where the supported Cu(II)Cl 2 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 Cu 2+.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 + /Cu 2+ catalyst is required to support CO chemisorption.

The interaction of CO with a copper(ii) chloride oxy-chlorination catalyst

“…This outcome connects with a previous communication concerning CO exposure to this catalyst at elevated temperatures. 15 However, this outcome is not that expected from Equation…”

“…9 We have previously used X-ray absorption spectroscopy to investigate the catalyst under consideration here. 15 XANES measurements recorded on application of a temperature ramp up to a maximum temperature of 640 K showed a decrease in Cu 2+ character and at temperatures from 633 K onwards there was an increasing contribution from Cu + species; at 640 K the sample consisted of a mixture of Cu + and a small amount of Cu 2+ . 15 Page 13 of 28 Faraday Discussions…”

“…In an earlier study we used X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) together with DFT calculations to investigate the interaction of CO over the same 10% CuCl 2 /8% KCl/attapulgite catalyst under consideration here. 15 Interestingly, that work showed that for temperatures <673 K, CO exposure to the dried 10% CuCl 2 /8% KCl/attapulgite catalyst yielded no phosgene but, instead, CO 2 was selectively produced.…”

“…On the basis of calculated CO adsorption energies, DFT calculations indicated that a mixed of Cu + /Cu 2+ was required to support CO chemisorption. 15 In the present work, a micro-reactor arrangement is used to examine conditions that support phosgene production from continuous exposure of CO over the 10% CuCl 2 /8% KCl/attapulgite catalyst at elevated temperatures and ambient temperature. The article is constructed as follows.…”

“…19 to lead to reduction of Cu 2+ to Cu + , resulting in a mixture of Cu 2+ and Cu + . 15 This scenario indicates some discrepancy between the copper oxidation states in the bulk and at the surface of the CuCl 2 crystallites on thermal treatment.…”