Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology was employed to study the CO2 methanation reaction catalyzed by Ru/CeO2 (with oxygen vacancy in CeO2) and Ru/α-Al2O3 (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO2 catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce(3+), surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO2 methanation undergoes formate route over Ru/CeO2 catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO2 methanation undergoes CO route over Ru surface in Ru/α-Al2O3 with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO2 methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO2 catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al2O3 (125 vs 250 °C).

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 (Niδ−). Moreover, the creation of a Niδ−–O v –Ti3+ interface site (O v 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 ∼7 times larger than the conventional 15%Ni/TiO2(450) catalyst. Such a high catalytic efficiency is attributed to the interfacial site (Niδ−–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 Niδ− and oxygen vacancy toward WGSR.

Layered double hydroxides (LDHs) are a class of clays with brucite-like layers and intercalated anions which have attracted increasing interest in the field of catalysis. Benefiting from the atomic-scale uniform distribution of metal cations in the brucite-like layers and the ability to intercalate a diverse range of interlayer anions, LDHs display great potential as precursors/supports to prepare catalysts, in that the catalytic sites can be preferentially orientated, highly dispersed, and firmly stabilized to afford excellent catalytic performance and recyclability. The approaches to prepare catalysts based on LDH materials include, but are not limited to, exfoliation of the brucite-like layers, lattice orientation/lattice confinement by the brucite-like layers, and intercalation. This Feature Article summarizes the latest developments in the design and preparation of nanocatalysts by using LDHs as precursors/supports.

A hierarchical CoNi-sulfide nanosheet array is fabricated via an in situ reduction of CoNi-layered double hydroxide (LDH) nanosheets, then a vulcanization process. The material inherits the morphology of the LDH precursor, consisting of well-distributed CoNi-alloy@CoNi-sulfide nanoparticles with a core-shell structure, and demonstrates promising performance toward hydrazine electrooxidation.

How to achieve supported metal nanocatalysts with simultaneously enhanced activity and stability is of vital importance in heterogeneous catalysis and remains a challenging goal. In this work, a surface defect-promoted Ni nanocatalyst with a high dispersion and high particle density embedded on a hierarchical Al 2 O 3 matrix was fabricated via a facile method involving an in situ reduction process, which exhibits excellent activity and stability simultaneously for the reaction of CO 2 methanation. HRTEM, HAADF-STEM, EXAFS, and positron annihilation spectroscopy demonstrate the existence of abundant surface vacancy clusters that serve as active sites, accounting for the significantly enhanced lowtemperature activity of the supported Ni nanoparticles. In addition, the anchoring effect from the support gives rise to a high reaction stability, without sintering and/or aggregation of active species during long-term use.

We report a new synthetic strategy for the fabrication of several supported nickel phosphides (Ni 12 P 5 , Ni 2 P, and NiP 2 ) with particle size ranging in 5−15 nm via a two-step procedure: preparation of supported Ni particles from layered double hydroxide precursors, followed by a further reaction with certain amount of red phosphorus. The selective hydrogenation of phenylacetylene over these metal phosphides was evaluated, and the as-prepared Ni 2 P/Al 2 O 3 catalyst show a much higher selectivity to styrene (up to 88.2 %) than Ni 12 P 5 /Al 2 O 3 (48.0 %), NiP 2 /Al 2 O 3 (65.9 %) and Ni/Al 2 O 3 (0.7 %) catalysts. EXAFS and in situ IR measurements reveal that the incorporation of P increases the bond length of Ni−Ni, which imposes a key influence on the adsorption state of alkene intermediates: as the Ni−Ni bond length extends to 0.264 nm, the alkene intermediate undergoes di-π(C=C) adsorption, facilitating its desorption and the resulting enhanced selectivity. Moreover, electron transfer occurs from Ni to P, as confirmed by EXAFS, XPS and in situ CO-IR experiment, in which the positively-charged Ni reduces the desorption energy of alkene and thus improves the reaction selectivity.

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The sustainable development of carbon recycling has attracted considerable attention from the viewpoint of the environment and resources. Herein, Ni nanoparticles (NPs) immobilized on a TiO 2 support were synthesized via a deposition-precipitation method followed by a calcination-reduction process (denoted as Ni/TiO 2 -DP), which can be used as a promising heterogeneous catalyst towards CO 2 methanation.Transmission electron microscope (TEM) images show that Ni NPs are highly dispersed on the TiO 2 surface (particle size: 2.2 nm), with a low Ni-Ni coordination number revealed by the hydrogen temperature programmed desorption (H 2 -TPD) and extended X-ray absorption fine structure (EXAFS) techniques. Moreover, the catalyst with a Ni loading of 15 wt% exhibits excellent catalytic behavior towards CO 2 methanation (conversion: 96%; selectivity: 99%) at a reaction temperature as low as 260 1C. The good dispersion of Ni NPs with large unsaturation facilitates a high exposure of active sites, which accelerates the formation of surface-dissociated hydrogen and the subsequent hydrogenation removal of surface nickel carbonyl species, accounting for the resulting enhanced low-temperature catalytic performance.