TiO2-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 TiO2-x-modified Ni nanocatalyst with tunable Ni-TiO2-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-TiO2-x interaction, which results in an increased coverage degree of Ni nanoparticles by TiO2-x as well as electron density of interfacial Ni (Nis-). Moreover, the creation of a Ni delta-,-O-v-Ti3+ interface site (O-nu denotes oxygen vacancy) induced by strong Ni-TiO2-x interaction serves as dual-active site to efficiently catalyze the water-gas shift reaction (WGSR). The optimized catalyst (Ni@TiO2-x(450)) via tuning Ni-TiO2-x interaction gives a TOF value of 3.8 s(-1) which is similar to 7 times larger than the conventional 15%Ni/TiO2(450) catalyst. Such a high catalytic efficiency is attributed to the interfacial site (Ni delta-,O-nu-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 delta- and oxygen vacancy toward WGSR.