TiO_2–x-Modified Ni Nanocatalyst with Tunable Metal–Support Interaction for Water–Gas Shift Reaction

The modulation of strong metal–support interaction (SMSI) plays a key role and remains a challenge in achieving the desired catalytic performance in many important chemical reactions. Herein, we report a TiO_2–x-modified Ni nanocatalyst with tunable Ni–TiO_2–x interaction via a two-step procedure: preparation of Ni/Ti mixed metal oxide (NiTi–MMO) from NiTi-layered double hydroxide (NiTi–LDH) precursor, followed by a further reduction treatment at different temperatures. A combination study (XRD, TEM, H₂-TPR, XPS, and in situ EXAFS) verifies that a high reduction temperature enhances the Ni–TiO_2–x interaction, which results in an increased coverage degree of Ni nanoparticles by TiO_2–x as well as electron density of interfacial Ni (Ni^δ−). Moreover, the creation of a Ni^δ−–O_v–Ti³⁺ interface site (O_v denotes oxygen vacancy) induced by strong Ni–TiO_2–x interaction serves as dual-active site to efficiently catalyze the water–gas shift reaction (WGSR). The optimized catalyst (Ni@TiO_2–x(450)) via tuning Ni–TiO_2–x interaction gives a TOF value of 3.8 s^–1, which is ∼7 times larger than the conventional 15%Ni/TiO₂(450) catalyst. Such a high catalytic efficiency is attributed to the interfacial site (Ni^δ−–O_v–Ti³⁺) with medium strength of metal–support interaction, as revealed by in situ diffuse reflectance Fourier transform infrared spectroscopy (in situ DRIFTS), which promotes the synergic catalysis between Ni^δ− and oxygen vacancy toward WGSR.