A strategy for low-temperature synthesis of hydrotalcite-based nickel phosphide catalysts (Ni2P-Al2O3) with flower-like porous structures was proposed. The in situ reduction of red phosphorus at 500 °C enables Ni2P catalysts with small particle size and abundant active and acidic sites, which facilitate the activation of substrates and H2. In the hydrodeoxygenation of guaiacol, a 100% conversion and 94.5% yield of cyclohexane were obtained over the Ni2P-Al2O3 catalyst under 5 MPa H2 at 250 °C for 3 h. Other lignin-derived phenolic compounds could also afford the corresponding alkanes with yields higher than 85%. Moreover, Ni2P-Al2O3 exhibited high hydrodeoxygenation activity in the deconstruction of more complex wood structures, including lignin oil and real lignin. Among the two different types of Ni sites of Ni(1) and Ni(2) in Ni2P, density functional theory (DFT) calculations showed that the Ni(2) site, highly exposed on the Ni2P-Al2O3 surface, possesses a stronger ability to break C–OH bonds during the hydrodeoxygenation of guaiacol in comparison with the Ni(1) site.

Surface lattice oxygen is crucial to the degradation of volatile organic compounds (VOCs) over transition metal oxides according to the Mars–van Krevelen mechanism. Herein, λ-MnO2 in situ grown on the surface of CoMn spinel was prepared by acid etching of corresponding spinel catalysts (CoMn-Hx-Ty) for VOC oxidation. Experimental and relevant theoretical exploration revealed that acid etching on the CoMn spinel surface could decrease the electron cloud density around the O atom and weaken the adjacent Mn–O bond due to the fracture of the surface Co–O bond, facilitating electron transfer and subsequently the activation of surface lattice oxygen. The obtained CoMn-H1-T1 exhibited an excellent catalytic performance with a 90% acetone conversion at 149 °C, which is 42 °C lower than that of CoMn spinel. Furthermore, the partially maintained spinel structure led to better stability than pure λ-MnO2. In situ diffuse reflectance infrared Fourier transform spectroscopy confirmed a possible degradation pathway where adsorptive acetone converted into formate and acetate species and into CO2, in which the consumption of acetate was identified as the rate-limiting step. This strategy can improve the catalytic performance of metal oxides by activating surface lattice oxygen, to broaden their application in VOC oxidation.

Selective catalytic oxidation of NH3 is the most promising method for removing low-concentration NH3. However, achieving high activity and N2 selectivity remains a great challenge. A Ag/CeSnO x tandem catalyst with dual active centers was designed and synthesized, which couples the NH3 over-oxidation on the noble metal active sites with NO x reduction on the support. The tandem catalyst exhibited excellent NH3 selective catalytic oxidation (NH3–SCO) performance at 200–400 °C. Based on various characterization techniques and DFT calculations, it was identified that the silver species on the Ag/CeSnO x catalysts existed as AgO nanoparticles (AgO NPs), and the electrons on the support were more easily transferred to AgO NPs, which promoted the oxidation activity of AgO and the reduction performance of the CeSnO x support. The coupling between the AgO NPs and CeSnO x helped balance the NH3 oxidation rate and the NO x reduction rate. In addition, the uniform adsorption of gaseous NH3 on the oxidation and reduction sites was also demonstrated by theoretical calculations, which is a prerequisite for tandem catalysis. By in situ DRIFTS, we revealed that the NH3–SCO reaction over Ag/CeSnO x catalysts mainly follows the internal selective catalytic reduction mechanism. It was characterized by excessive oxidation of NH3 to NO x on AgO NPs. At a temperature lower than 200 °C, NO x was reduced to N2 by the adsorbed NH3 on the AgO. When the temperature was higher than 200 °C, NO x was reduced to N2 by NH3 or NH4 + adsorbed on the CeSnO x support. Therefore, the charge transfer at the Ag/CeSnO x catalyst interface and the coordination of atomic scale catalytic sites have realized the conversion of NH3 to N2 through NO x in a tandem catalytic mode.

The severe hazard of chlorinated volatile organic compounds (CVOCs) to human health and the natural environment makes their abatement technology a key topic of global environmental research. Due to the existence of Cl, the byproducts of CVOCs in the catalytic combustion process are complex and toxic, and the possible generation of dioxin becomes a potential risk to the environment. Well-qualified CVOC catalysts should process favorable low-temperature catalytic oxidation ability, excellent selectivity, and good resistance to poisoning, which are governed by the reasonable adjustment of acidity and redox properties. This review overviews the application of different types of multicomponent catalysts, that is, supported noble metal catalysts, transition metal oxide/zeolite catalysts, composite transition metal oxide catalysts, and acid-modified catalysts, for CVOC degradation from the perspective of balance between acidity and redox properties. This review also highlights the synergistic degradation of CVOCs and NO x from the perspective of acidity and redox properties. We expect this work to inspire and guide researchers from both the academic and industrial communities and help pave the way for breakthroughs in fundamental research and industrial applications in this field.

Sample morphology is known to have a significant influence on catalytic performance due to changes in catalysts’ crucial properties such as active sites, oxygen vacancies, and active oxygen species. It is worthwhile revealing the differences in catalyst properties and reaction mechanisms for modified catalysts with different morphologies. Herein, MnO2 was grown in situ on platelike CoAlO (denoted as CoAlO-P) and flowerlike CoAlO (denoted as CoAlO-F) for high-efficiency oxidation of volatile organic compounds, in which platelike MnO2/CoAlO-P exhibited a low T 90% of 175 °C, good stability, and water resistance. Experimental and theoretical results revealed that in comparison with CoAlO-F, MnO2 modification of platelike CoAlO-P led to predominant exposure of Co species and weak Co–O bond due to the strong interaction between CoAlO-P and MnO4 –, which promoted the adsorption/activation of acetone. The oxygen vacancy generated from breaking a Co–O bond adjacent to Mn on MnO2/CoAlO-P was shown to have a strong capacity to dissociate O2 into active oxygen species, accelerating the conversion of formate, acetate, and aldehyde intermediate species into CO2 and H2O. This investigation will guide the rational design of catalysts for application in hydrocarbon oxidation reactions.