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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-06, Vol.8 (22), p.11282-11291
• Main Authors: Leung, Alice H. M, García-Trenco, Andrés, Phanopoulos, Andreas, Regoutz, Anna, Schuster, Manfred E, Pike, Sebastian D, Shaffer, Milo S. P, Williams, Charlotte K
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Benchmarks; Carbon dioxide; Catalysis; Catalysts; Colloids; Continuous flow; Continuously stirred tank reactors; Copper; Crystallography; Dopants; Doping; Hydrogenation; Hydrolysis; Inductively coupled plasma; Interfaces; Liquid phases; Magnesium; Mesitylene; Methanol; Nanocatalysis; Nanoparticles; Optical emission spectroscopy; Photoelectron spectroscopy; Photoelectrons; Selectivity; Spectrometry; Spectroscopy; Transmission electron microscopy; X ray photoelectron spectroscopy; X-ray crystallography
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta00509f

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 CO 2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO 2  : H 2 = 1 : 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-Al 2 O 3 [480 μmol mmol metal −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. Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors.