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Non-vanadium-based catalysts with high SO2tolerance are still interesting in selective catalytic reduction of NO by NH3(NH3-SCR) and SO2adsorption 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 TiO2catalysts and studied their SO2tolerance for the first time. Owing to suitable surface acidity and reducibility, ReOx/TiO2catalysts exhibited satisfactory activity in a wide temperature range of 250–350 °C. As expected, experimental results and DFT calculations indicated that SO2adsorption on ReOx/TiO2catalysts was rather weak, thus the catalysts performed excellent SO2tolerance in the NH3-SCR reaction. Moreover, in situDRIFTS indicated that the NH3-SCR reaction on ReOx/TiO2catalysts followed the Eley–Rideal mechanism and SO2had little effect on the reaction mechanism. Our findings should provide new insights into the development of SCR catalysts with high SO2tolerance.

It is of great significance to design highly active and stable catalysts for CO oxidation. Herein, a Pt/In–SnO2catalyst was firstly fabricated viaa facile hydrothermal reaction coupled with photoreduction strategy, achieving 1 vol% of CO totally oxidized at just 145 °C, over 200 °C lower than that of Pt/SnO2. Moreover, Pt/In–SnO2demonstrates superior catalytic stability and recyclability under both dry and humid conditions. Incorporation of In cations results in marked structure distortion of SnO2, promoting the formation of oxygen vacancies and enhancing the concentration and mobility of reactive oxygen species. Abundant Pt sites over Pt/In–SnO2further accelerate CO adsorption and activation. Density functional theory results prove that the energy barrier of CO oxidation reduces from 0.85 to 0.75 eV after In doping and the produced CO2can desorb spontaneously from the catalyst surface, which accelerates the CO oxidation process. This work provides new ideas for designing robust catalysts for low-temperature CO elimination.

Optimizing the interaction between metal active centers and supports by tuning crystal facets is an effective strategy to improve the activity and stability of catalysts. Herein, α-MnO2nanowires with different exposed crystal facets (respectively (310), (110) and (100)) were synthesized viaa facile hydrothermal method to promote the activity of an Au/α-MnO2catalyst for propane combustion. Results reveal that Au/α-MnO2-110 exhibits the highest catalytic activity, achieving 90% propane (2500 ppm) conversion at just 216 °C (apparent activation energy as low as 50.2 kJ mol−1). Compared with Au/α-MnO2-310 and Au/α-MnO2-100, Au/α-MnO2-110 with the largest quantity of oxygen vacancies, strong reducibility, and high surface oxygen mobility possesses the best capability for adsorbing and activating oxygen molecules. DFT results reveal that the (110) facet of α-MnO2has the lowest formation energy of oxygen vacancies (Evo(110) = 0.6 eV), suggesting the presence of weak surface Mn–O bonds, facilitating the formation of Auδ+species and therefore promoting C–H bond breaking in propane. This work highlights a new strategy for the design of efficient catalysts for stable light alkane low-temperature decomposition by surface exposed facet engineering.

Iron vanadate (FeVO4) nanorods are used as a carrier to support manganese (Mn) and cerium (Ce) oxides for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3for the first time. Among these developed Ce–Mn/FeVO4catalysts with different molar ratios of Ce/Mn, the Ce0.2Mn0.2/FeVO4catalyst exhibits the best de-NOxperformance and N2selectivity, which are higher than 90% in a wide temperature window of 90–420 °C. Through a series of characterization techniques, it is found that the synergistic effect between Ce and Mn enhances the reduction ability and the number of acid sites on the catalyst, which facilitates the adsorption and conversion of flue gas. The introduction of an appropriate ratio of Ce/Mn increases the concentration of Mn4+and chemisorbed oxygen (OS) on the catalyst, leading to a “fast SCR reaction” with oxidizing NO to NO2, which significantly improves the low-temperature de-NOxefficiency. In addition, the interaction between the active components (Ce/Mn) and the support (FeVO4) increases the de-NOxperformance of Ce0.2Mn0.2/FeVO4at high temperatures. In the meantime, the Mn4++ Ce3+↔ Mn3++ Ce4+reduction electron pair formed between Ce and Mn promotes the transport of electrons, which is also beneficial for the SCR reaction at low temperature. The in situdiffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that the SCR reaction over Ce0.2Mn0.2/FeVO4catalyst follows both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) reaction mechanisms.

The development of noble metal free and highly active cocatalysts is critically important and also challenging for the practical applications of photocatalytic hydrogen production. Here, ultrafine MoO2cocatalyst nanoparticles (≤10 nm) were in situsolvothermally synthesized on carbon nitride nanosheets (CNSs). We found that the ultrafine MoO2nanoparticle decorated CNS exhibits higher electrocatalytic hydrogen evolution reaction (HER) performance than Pt–CNS. Besides, CNS with a curly thin nanosheet structure has an increased specific surface area and broadened bandgap after the solvothermal process compared to bulk carbon nitride (CN). Characterization results reveal that the strong interfacial interaction between metallic MoO2and CNS greatly promotes the photogenerated electrons extracted from CNS to MoO2, resulting in efficient electron excitation and charge transfer in the composite. Accordingly, the hydrogen production rate of 1.0 wt% MoO2/CNS is 3.4 and 1.6 times higher than that of the same mass noble-metal Pt loaded CN and CNS under visible light irradiation, respectively. This work may provide a guide for constructing non-noble metal cocatalyst modified materials for efficient photocatalytic hydrogen production.

Nitric oxide (NO) emitted from the combustion of fossil fuels has drawn global concern, and the oxidation of NO contributes greatly to the DeNOxprocess. Herein, single-crystal γ-MnO2catalysts with well-defined hollow-sphere-, sea-urchin-, and flower-like morphologies (γ-MnO2-HS, γ-MnO2-SU, and γ-MnO2-F) were rationally designed and synthesized viaan environmental-friendly template-free hydrothermal strategy. The physicochemical properties of the prepared materials were characterized by XRD, FE-SEM, TEM, BET, XPS, H2-TPR, O2/NO-TPD and in situDRIFTS, and their catalytic activities in NO oxidation were evaluated. The results showed the γ-MnO2-HS sample possessed the highest activity and could oxidize 91.1% of NO at 275 °C, which was obviously higher than those of the γ-MnO2-SU and γ-MnO2-F catalysts. It was found that the presence of abundant surface-adsorbed oxygen and the largest quantity of Mn3+over the γ-MnO2-HS material respectively accelerated the processes of NO adsorption and O2activation, which greatly promoted the NO oxidation process. This work provides significant insights into NO oxidation over γ-MnO2catalysts.

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-MnO2nanorods 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/MnO2sample has the highest activity and can destroy 90% toluene (1000 ppm) at just 226 °C with a reaction rate of 3.39 × 10−4mol gcat−1s−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-MnO2structure, promote the formation of MnO6–K–MnO6bridging 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-MnO2surface 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.

Manganese-based metal oxides are promising catalysts for the NH3-SCR (selective catalytic reduction) of NOxat low temperatures. However, manganese-based catalysts usually exhibit poor SO2and H2O tolerance. In order to overcome the fatal shortcoming, non-manganese-based CuyCe1−yW5Oxcatalysts (y= 0, 0.4, 0.5, 0.6, 1.0) are synthesized successfully by a standard co-precipitation method, and the catalytic performances of these catalysts are tested by the NH3-SCR of NOx. The results show that there are synergistic effects between Cu and Ce, which affect the CuyCe1−yW5Oxcatalysts in many aspects, such as the specific surface area, the surface contents of Ce3+and Cu2+, the reductive strength and the amount of weak and strong acid sites on the surface. Moreover, the synergistic effects also have an impact on the de-NOxmechanism of CuyCe1−yW5Oxcatalysts, and finally decide their catalytic performances. Among all the CuyCe1−yW5Oxcatalysts, the Cu0.5Ce0.5W5Oxcatalyst shows the best catalytic de-NOxperformance and good tolerance to SO2and H2O poisoning. This work may provide a suggestion for the design of non-manganese-based SCR catalysts with the desired de-NOxperformance and good SO2tolerance by making use of the synergistic effects between different metal oxides.

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 CuCeOxcatalyst, which leads to a remarkable increase in catalytic activity in the oxidation of toluene. Among these catalysts, the CuHoCeOxcatalyst 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 CuCeOxframework, 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 CuCeOxbinary 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 CuHoCeOxsample are proposed by means of in situDRIFTS 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 CO2and H2O.

Developing photocatalysts with efficient spatial charge separation and transfer as well as a high light-harvesting ability remains a key challenge. Here, we report a facile in situprocess to decorate ultrathin g-C3N4nanosheets (NSs) with a co-catalyst, Cu2MoS4, for photocatalytic water splitting. The as-obtained Cu2MoS4/g-C3N4exhibits a superior photocatalytic H2evolution rate of 2170.5 μmol h−1g−1under visible light irradiation, which is nearly 677 and 34 times higher than that of bulk g-C3N4and g-C3N4NSs, respectively, and far exceeds that of most g-C3N4catalysts modified with other sulphide co-catalysts reported in the literature, demonstrating that Cu2MoS4can serve as a promising non-noble metal co-catalyst to couple with g-C3N4for highly efficient photocatalysts. Structural characterization confirms the well-defined morphology of Cu2MoS4/g-C3N4in which Cu2MoS4hollow spheres are uniformly attached on the ultrathin g-C3N4NSs with numerous micropores and vacancies. The optical properties indicate that Cu2MoS4/g-C3N4possesses a superb visible light absorption ability. The photoluminescence spectra, photocurrent response, and electrochemical impedance spectra combine to prove the highly efficient separation and migration of photogenerated electrons and holes. All these factors synergistically enhance the photocatalytic activity of Cu2MoS4/g-C3N4for photocatalytic water splitting, providing new insights into the rational design of high-performance visible light-driven photocatalysts based on earth-abundant elements.

MnOxoxides with different morphologies (nanowire (MnOx-W), nanocube (MnOx-C), nanorod (MnOx-R), and nanosphere (MnOx-S)) and exposed facets were synthesized viaa 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 Mn3O4is 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 CO2at 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 Mn3O4have 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 situDRIFTS and TPSR results indicate that the mineralization of MEK into CO2over 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.

A series of CuSO4/TiO2binary oxide catalysts with different CuSO4loadings (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 viaN2adsorption/desorption, XRD, Raman, NH3-TPD, NO-TPD, H2-TPR, XPS, and in situDRIFTS. The CuSO4content had significant influence on catalytic activity. High CuSO4loading favored the solid reaction between CuSO4and 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, NH3oxidation increased with CuSO4loading and caused NOxconversion to decrease when the CuSO4loading was higher than 10 wt%. Thus, the sample with 10 wt% CuSO4loading presented the broadest temperature window and it also showed an excellent resistant to SO2and H2O. Both Brønsted and Lewis acid sites were formed on the catalyst. S–OH of sulfate and sulfite were the main reason for formation of Brønsted acid sites. NH3-SCR reaction on CuSO4/TiO2followed the Eley–Rideal mechanism: NH3first adsorbed on Brønsted and Lewis acid sites as NH4+and NH3, then reacted with gaseous NO and O2to form N2and H2O.

Pure ceria catalysts were prepared by a facile modified homogeneous co-precipitation method, and their catalytic performance was evaluated in the soot oxidation reaction. The structure and textural properties of the synthesized catalysts were characterized viaXRD, N2adsorption/desorption, TG-DSC-MS, H2-TPR, FE-SEM, HR-TEM and XPS techniques. It is shown that CeO2samples prepared by the improved co-precipitation method exhibit obviously better catalytic activity than those prepared by the conventional co-precipitation method. The CeO2-CP4-F sample shows the best activity, for which the peak temperature, Tp, values of soot combustion are about 465 °C in O2stream gas and 430 °C in a NO/O2stream under soot/catalyst “loose contact” conditions. Moreover, after high temperature aging, the activity of CeO2-CP4-A becomes even better, for which the Tpvalue of soot combustion is lowered to 445 °C in O2air gas. The catalytic activity is not well associated with the physicochemical properties of BET surface area, particle size and reducibility at low temperatures. The number of lattice oxygen and its mobility in the series of CeO2may be the crucial factor to decide the overall catalytic performance. According to the HRTEM result, the excellent migration of lattice oxygen may result from the preferential exposure of more-reactive planes, which may be the essential reason to explain the good performance of CeO2catalysts in soot oxidation.