One-Step Synthesis of AuCu/TiO2 Catalysts for CO Preferential Oxidation

Catarine Santos Lopes Alencar,Julio Cesar Martins Da Silva,Ana Rita Noborikawa Paiva,Jorge Moreira Vaz,Estevam Vitorio Spinacé

doi:10.1590/1980-5373-mr-2020-0181

Catarine Santos Lopes Alencar, Julio Cesar Martins Da Silva + Show 3 more

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https://doi.org/10.1590/1980-5373-mr-2020-0181

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Abstract

Au/TiO2 (1wt% Au), Cu/TiO2 (1wt% Cu) and AuCu/TiO2 (1wt% AuCu) catalysts with different Au:Cu mass ratios were prepared in one-step synthesis using sodium borohydride as reducing agent. The resulting catalysts were characterized by X-ray diffraction (XRD), X-ray Dispersive Energy (EDX), Transmission Electron Microscopy (TEM) and Temperature Programmed Reduction (TPR) and tested for the preferential oxidation of carbon monoxide (CO-PROX reaction) in H2-rich gases. EDS analysis showed that the Au contents are close to the nominal values whereas for Cu these values are always lower. X-ray diffractograms showed only the peaks of TiO2 phase; no peaks of metallic Au and Cu species or oxides phases were observed. TPR and high-resolution TEM analysis showed that AuCu/TiO2 catalysts exhibited most of Au in the metallic form with particles sizes in the range of 3-5 nm and that Cu was found in the form of oxide in close contact with the Au nanoparticles and well spread over the TiO2 surface. The AuCu/TiO2 catalysts exhibited good performance in the range of 75-100 °C and presented a better catalytic activity when compared to the monometallic ones. A maximum CO conversion of 98.4% with a CO2 selectivity of 47% was obtained for Au0.50Cu0.50/TiO2 catalyst at 100oC.

Highlights

Hydrogen gas is produced predominantly by combining the methane steam reforming and the gas-water shift reactions resulting in a hydrogen-rich mixture containing about 1% of carbon monoxide (10.000 ppm of CO)
The purification of the hydrogenrich mixture is necessary and one process that has been considered very promising is the preferential oxidation of CO in hydrogen-rich mixtures (CO-PROX reaction), because it can dramatically reduce energy and hydrogen losses when compared to the processes currently used in the industry such as CO methanation and pressure swing adsorption (PSA)
It was observed that the amounts of Au and Cu determined by Energy-dispersive X-ray spectroscopy (EDS) increase with the increase of the nominal values; the values determined for Au are close to the nominal values, while for Cu these values are always smaller than the nominal ones

Summary

Introduction

Hydrogen gas is produced predominantly by combining the methane steam reforming and the gas-water shift reactions resulting in a hydrogen-rich mixture containing about 1% of carbon monoxide (10.000 ppm of CO). This CO level is not sufficiently low for application of hydrogen in Proton Exchange Membrane Fuel Cell (PEMFC) and in ammonia synthesis because CO poison the catalysts used in these processes[1,2,3,4,5]. The catalytic activities of the resulting AuCu catalysts for CO-PROX showed a significant enhancement when compared to CuO and Cu2O materials. The catalysts were characterized and tested for CO-PROX reaction

Experimental

Characterizations

Catalytic tests

Results and Discussion

Conclusions