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The alkali metal potassium has the functions of structure promotion and electronic modulation in metal oxides. Herein, diverse potassium precursors (KOH, KNO3, K2SO4, and KCl) were introduced to α-MnO2 nanorods through a facile post-processing strategy. The presence of potassium species has a remarkable promotion effect on the catalytic performance of α-MnO2. Amongst them, the KOH/MnO2 sample has the highest activity and can destroy 90% toluene (1000 ppm) at just 226 °C with a reaction rate of 3.39 × 10−4 mol gcat−1 s−1, which is over 20 times higher than that of pure α-MnO2. Different anions in the potassium precursors bring a distinct mutation in the α-MnO2 structure, promote the formation of MnO6–K–MnO6 bridging bonds in α-MnO2, and exhibit obvious diverse abilities for balancing charge transfer. KOH is identified as the most promising precursor for alkali metal modification, which significantly improves the distribution of K species over the α-MnO2 surface and strengthens the content and activity of lattice oxygen. It is confirmed that the lattice oxygen plays a key role in the catalytic oxidation of toluene over α-MnO2, which follows the Mars–van Krevelen mechanism. Positive hole defects (Mn3+) caused by KOH treatment play an important role in the diffusion of O and enhance the reducibility of manganese oxide. In addition, the enhanced specific surface area, pore volume, and surface acidity are also conducive for the catalytic oxidation of toluene.

Non-vanadium-based catalysts with high SO2 tolerance are still interesting in selective catalytic reduction of NO by NH3 (NH3-SCR) and SO2 adsorption is the foremost step for the deactivation of catalysts. In order to alleviate the adsorption of SO2, we fabricated a series of rhenium (Re; without stable sulfate) supported TiO2 catalysts and studied their SO2 tolerance for the first time. Owing to suitable surface acidity and reducibility, ReOx/TiO2 catalysts exhibited satisfactory activity in a wide temperature range of 250–350 °C. As expected, experimental results and DFT calculations indicated that SO2 adsorption on ReOx/TiO2 catalysts was rather weak, thus the catalysts performed excellent SO2 tolerance in the NH3-SCR reaction. Moreover, in situ DRIFTS indicated that the NH3-SCR reaction on ReOx/TiO2 catalysts followed the Eley–Rideal mechanism and SO2 had little effect on the reaction mechanism. Our findings should provide new insights into the development of SCR catalysts with high SO2 tolerance.

MnOx oxides with different morphologies (nanowire (MnOx-W), nanocube (MnOx-C), nanorod (MnOx-R), and nanosphere (MnOx-S)) and exposed facets were synthesized via a solvothermal method. The catalytic performance of the synthesized MnOx materials for methyl ethyl ketone (MEK) destruction was investigated. Results show that the activity of MnOx-W with highly exposed {101} facets of Mn3O4 is superior to that of MnOx-C, MnOx-R, and MnOx-S exposing {321} facets of Mn2O3, {110} facets of MnO2, and {101} and {112} facets of Mn3O4, respectively. MEK can be completely mineralized into CO2 at 195 °C over MnOx-W under a relatively high gas hourly space velocity of 37 200 h−1, which is even better than some typical noble metal loaded catalysts. The lowest apparent activation energy of MnOx-W (27.7 kJ mol−1) for MEK destruction also confirms its excellent catalytic activity. Density functional theory (DFT) results reveal that the {101} facets of Mn3O4 have the highest MEK adsorption energy (0.79 eV), which indicates that MEK molecules have a high affinity to adsorb onto the MnOx-W surface, promoting the oxidation process of MEK. In situ DRIFTS and TPSR results indicate that the mineralization of MEK into CO2 over MnOx-W goes through an oxidation route with diacetyl as the primary intermediate. We found that the highly exposed {101} active facets, abundant oxygen vacancies, and excellent low-temperature reducibility are responsible for the superior oxidation performance of MnOx-W. This finding may bring new insights into the designing of highly effective catalysts and has implications for a wide range of reactions not limited to MEK oxidation.

Novel CuMCeOx (M = Y, Eu, Ho, and Sm) trimetal oxide catalysts with developed mesoporosity and an enhanced oxygen migration capability were fabricated by a reproducible self-precipitation approach for the first time. The incorporation of a rare-earth element (especially Y, Eu, and Ho) can increase the reducibility of, and mobility of surface adsorbed oxygen on, a CuCeOx catalyst, which leads to a remarkable increase in catalytic activity in the oxidation of toluene. Among these catalysts, the CuHoCeOx catalyst possesses the highest oxidation activity, with the complete mineralization of toluene at 220 °C at a relatively high GHSV of 50 000 h−1, which is ascribable to the synergetic effect of Ho and the CuCeOx framework, which creates abundant active oxygen vacancies over mixed oxides. Raman spectroscopy and density functional theory (DFT) studies reveal that Ho element is coordinated to two oxygen atoms and occupies the site of a Ce atom, which changes the π-bonding of Ce in the CuCeOx binary oxide and thus leads to the weakening of Ce–O bonds and an enhanced oxygen storage capacity. A possible reaction pathway and a mechanism for the combustion of toluene over a CuHoCeOx sample are proposed by means of in situ DRIFTS and DFT studies, which prove that the toluene oxidation process obeys the Mars–van Krevelen mechanism, with aldehydes and ketones as the primary organic intermediates, before decomposition to CO2 and H2O.

A series of CuSO4/TiO2 binary oxide catalysts with different CuSO4 loadings (0–20 wt%) were prepared by a facile solid state impregnation protocol. The physicochemical properties of the catalysts and the NO reaction route were extensively characterized via N2 adsorption/desorption, XRD, Raman, NH3-TPD, NO-TPD, H2-TPR, XPS, and in situ DRIFTS. The CuSO4 content had significant influence on catalytic activity. High CuSO4 loading favored the solid reaction between CuSO4 and TiO2, promoted the formation of sulfite and weak acid sites, and obviously increased the activity at temperatures below 340 °C. However, at a temperature higher than 340 °C, NH3 oxidation increased with CuSO4 loading and caused NOx conversion to decrease when the CuSO4 loading was higher than 10 wt%. Thus, the sample with 10 wt% CuSO4 loading presented the broadest temperature window and it also showed an excellent resistant to SO2 and H2O. Both Bronsted and Lewis acid sites were formed on the catalyst. S–OH of sulfate and sulfite were the main reason for formation of Bronsted acid sites. NH3-SCR reaction on CuSO4/TiO2 followed the Eley–Rideal mechanism: NH3 first adsorbed on Bronsted and Lewis acid sites as NH4+ and NH3, then reacted with gaseous NO and O2 to form N2 and H2O.