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Cu/M:ZnO (M = Mg, Al, Cu) colloidal nanocatalysts for the solution hydrogenation of carbon dioxide to methanol

DOI: 10.1039/D0TA00509F DOI Help

Authors: Alice H. M. Leung (University of Oxford) , Andrés García-trenco (University of Oxford) , Andreas Phanopoulos (University of Oxford) , Anna Regoutz (University College London) , Manfred E. Schuster (Johnson Matthey Technology Centre) , Sebastian Pike (University of Oxford) , Milo S. P. Shaffer (Imperial College London) , Charlotte K. Williams (University of Oxford)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Materials Chemistry A , VOL 25

State: Published (Approved)
Published: May 2020

Abstract: Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors. Substitutional doping of the wurtzite ZnO nanoparticles with 5 mol% Mg(II), Al(III) and Cu(I) is achieved by the addition of sub-stoichiometric amounts of the appropriate dopant [(n-butyl)(sec-butyl)magnesium, triethylaluminium or mesitylcopper] to diethylzinc in the precursor mixture. After hydrolysis, the resulting colloidal nanoparticles (sizes of 2–3 nm) are characterised by powder X-ray crystallography, transmission electron microscopy, inductively-coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. A solution of the doped-ZnO nanoparticles and colloidal Cu(0) nanoparticles [M:ZnO : Cu = 1 : 1] are applied as catalysts for the hydrogenation of CO2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO2[thin space (1/6-em)]:[thin space (1/6-em)]H2 = 1[thin space (1/6-em)]:[thin space (1/6-em)]3, 150 mL min−1, mesitylene, 20 h]. All the catalyst systems display higher rates of methanol production and better stability than a benchmark heterogeneous catalyst, Cu–ZnO–Al2O3 [480 μmol mmolmetal−1 h−1], with approximately twice the activity for the Al(III)-doped nanocatalyst. Despite outperforming the benchmark catalyst, Mg(II) doping is detrimental towards methanol production in comparison to undoped ZnO. X-Ray photoelectron spectroscopy and transmission electron microscopy analysis of the most active post-catalysis samples implicate the migration of Al(III) to the catalyst surface, and this surface enrichment is proposed to facilitate stabilisation of the catalytic ZnO/Cu interfaces.

Subject Areas: Materials, Chemistry

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