Publisher: American Chemical Society (ACS)

Issue: 9

License: http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html

Publication date(s): 2018/09/07 (print) 2018/07/27 (online)

Pages: 8493-8505

Volume: 8 Issue: 9

Journal: ACS Catalysis

Link: /doi/pdf/10.1021/acscatal.8b02232

URL: http://dx.doi.org/10.1021/acscatal.8b02232

Single-site Au species supported on carbon have been shown to be the active sites for acetylene hydrochlorination. The evolution of these single-site species has been monitored by Au L₃ X-ray absorption spectroscopy (XAS). Alternating between a standard reaction mixture of HCl/C₂H₂ and the single reactants has provided insights into the reaction mechanism and catalyst deactivation processes. We demonstrate that oxidative addition of HCl across an Au(I) chloride species requires concerted addition with C₂H₂, in accordance with both the XAS measurements of Au oxidation state and the reaction kinetics being first order with respect to each reactant. Excess C₂H₂ changes the Au speciation and results in the formation of oligomeric acetylene species which were detected by inelastic neutron scattering. Catalyst deactivation at extended reaction times can be correlated with the formation of metallic Au particles. These Au(0) species generated during the sequential gas experiments, or after prolonged reaction times, results in the analysis of the normalized near-edge white line intensity becoming an unsuitable guide for identifying the active Au species, affecting the strong correlation between normalized white line height and VCM productivity usually observed in the active catalyst. Thus, a combination of scanning transmission electron microscopy and detailed modeling of whole XAS spectrum was required to distinguish active Au(I) and Au(III) species from the spectator Au(0) component.