Black TiO2−x with stable surface oxygen vacancies as the support of efficient gold catalysts for water-gas shift reaction

Abstract

Exploring appropriate supports is a key step to prepare efficient water-gas shift (WGS) catalysts. In this sense, supports with some oxygen vacancies are preferable, but there have been no efficient methods to obtain abundant stable surface oxygen vacancies. Here, a black TiO_2−x support rich in stable surface oxygen vacancies was prepared by hydrogen-etching technology. More impressively, compared with the gold catalyst supported on traditional white TiO₂, the gold catalyst supported on black TiO_2−x has been proven to be an efficient and stable WGS catalyst. According to the in-depth characterization of its structural properties, the disordered layer and abundant stable surface oxygen vacancies of the black TiO_2−x support lead to higher microstrain and more metallic Au⁰ species, respectively, which are all in favor of higher WGS catalytic activities. Furthermore, we successfully linked the WGS thermocatalytic activities with the optoelectronic properties, and then tried to understand the WGS pathway from the view of an electron flow process. Hereinto, the Ohmic barrier has been decreased because of the narrowed forbidden band gap, which improves the transmission efficiency of “hot-electron flow”. Meanwhile, the abundant surface oxygen vacancies function as electron traps, thus promoting the flow of “hot-electrons” and reduction reaction of H₂O. As a consequence, the WGS catalytic activity is enhanced. The involved hydrogen-etching method resulting in abundant stable surface oxygen vacancies can be extended to other supported catalysts for WGS reaction or other thermocatalytic reactions.