Deactivation of a single-site gold-on-carbon acetylene hydrochlorination catalyst: An X-ray absorption and inelastic neutron scattering study

DOI: 10.1021/acscatal.8b02232

Authors: Grazia Malta (Cardiff Catalysis Institute, Cardiff University) , Simon A. Kondrat (Cardiff Catalysis Institute, Cardiff University; Loughborough University) , Simon J. Freakley (Cardiff Catalysis Institute, Cardiff University) , Catherine Davies (Cardiff Catalysis Institute, Cardiff University) , Simon Dawson (Cardiff Catalysis Institute, Cardiff University) , Xi Liu (Synfuels China Co. Ltd) , Li Lu (Lehigh University) , Krzysztof Dymkowski (Rutherford Appleton Laboratory) , Felix Fernandez-alonso (ISIS Facility; University College London) , Sanghamitra Mukhopadhyay (ISIS Facility; Imperial College London) , Emma Kate Gibson (UK Catalysis Hub; University of Glasgow) , Peter P. Wells (University College London) , Stewart F. Parker (ISIS Facility) , Christopher J. Kiely (Cardiff Catalysis Institute, Cardiff University) , Graham J. Hutchings (Cardiff Catalysis Institute, Cardiff University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Catalysis

State: Published (Approved)
Published: July 2018
Diamond Proposal Number(s): 10306 , 11398 , 15214

Abstract: 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 1st order with respect to each reactant. The addition of 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. The presence of this Au(0) species generated during the sequential gas experiments or after prolonged reaction times, results in the analysis of the normalised near edge white line intensity of the Au L3 X-ray absorption spectrum alone 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 modelling of whole XAS spectrum was required to distinguish active Au(I) and Au(III) species from the spectator Au(0) component.

Journal Keywords: Acetylene hydrochlorination; gold catalysis; heterogeneous catalysis; single-site catalysis; deactivation

Subject Areas: Chemistry


Instruments: B18-Core EXAFS