It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

Reducing carbon dioxide to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single atoms of palladium and platinum supported on graphitic carbon nitride (g-C3N4), i.e., Pd/g-C3N4 and Pt/g-C3N4, respectively, acting as photocatalysts for CO2 reduction were investigated by density functional theory calculations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from the hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, deposition of atom catalysts on g-C3N4 significantly enhances the visible-light absorption, rendering them ideal for visible-light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply.

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Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide.

Metal nanoparticles stabilized on a support material catalyse many major industrial reactions. Metal-support interactions in these nanomaterials can have a substantial influence on the catalysis, making metal-support interaction modulation one of the few tools able to enhance catalytic performance. This topic has received much attention in recent years, however, a systematic rationalization of the field is lacking due to the great diversity in catalysts, reactions and modification strategies. In this review, we cover and categorize the recent progress in metal-support interaction tuning strategies to enhance catalytic performance for various reactions. Furthermore, we quantify the productivity enhancements resulting from metal-support interaction control that have been achieved in C1 chemistry in recent years. Our analysis shows that up to fifteen-fold productivity enhancement has been achieved, and that metal-support interaction is most impactful for metal nanoparticles smaller than four nanometres. These findings demonstrate the importance of metal-support interaction to improve performance in catalysis. Methods to control the performance of heterogeneous catalysts are extremely relevant to the success of industrial processes. This review provides a rationalization of the effects that metal support interactions have on the reactivity of different catalytic systems, emphasizing strategies to tune such effects.

Control of metal-support interactions in heterogeneous catalysts to enhance activity and selectivity

Selective catalytic reduction with NH3 (NH3-SCR) is the most efficient technology to reduce the emission of nitrogen oxides (NOx) from coal-fired industries, diesel engines, etc. Although V2O5-WO3(MoO3)/TiO2 and CHA structured zeolite catalysts have been utilized in commercial applications, the increasing requirements for broad working temperature window, strong SO2/alkali/heavy metal-resistance, and high hydrothermal stability have stimulated the development of new-type NH3-SCR catalysts. This review summarizes the latest SCR reaction mechanisms and emerging poison-resistant mechanisms in the beginning and subsequently gives a comprehensive overview of newly developed SCR catalysts, including metal oxide catalysts ranging from VOx, MnOx, CeO2, and Fe2O3 to CuO based catalysts; acidic compound catalysts containing vanadate, phosphate and sulfate catalysts; ion exchanged zeolite catalysts such as Fe, Cu, Mn, etc. exchanged zeolite catalysts; monolith catalysts including extruded, washcoated, and metal-mesh/foam-based monolith catalysts. The challenges and opportunities for each type of catalysts are proposed while the effective strategies are summarized for enhancing the acidity/redox circle and poison-resistance through modification, creating novel nanostructures, exposing specific crystalline planes, constructing protective/sacrificial sites, etc. Some suggestions are given about future research directions that efforts should be made in. Hopefully, this review can bridge the gap between newly developed catalysts and practical requirements to realize their commercial applications in the near future.

Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts: State of the Art and Future Prospects.

Abatement of various types of VOCs by adsorption/catalytic oxidation: A review

High temperature reduction generally induces the sintering of supported noble metals, therefore resulting in a negative effect on their performance. Here, we show that high temperature reduction was able to dramatically increase the activity of Pd/TiO 2 for ambient HCHO oxidation. We prepared a Pd/TiO 2 catalyst and pre-reduced it with H 2 at low temperature (300 °C) and high temperature (450 °C), respectively, and then tested the activity for HCHO oxidation at ambient temperature. The Pd/TiO 2 -450R catalyst showed a much better performance than Pd/TiO 2 -300R at room temperature. 100% HCHO conversion could be obtained on the Pd/TiO 2 -450R catalyst at a GHSV of 95000 h −1 and 140 ppm inlet HCHO. The catalysts were then characterized by using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and other methods. The results indicate that high temperature reduction could induce the strong metal-support interaction (SMSI), decreasing the surface Pd particle size by partially encapsulating and trapping Pd clusters with TiO 2 , and also could produce more oxygen vacancies, beneficial to the activation of O 2 and formation of surface OH groups, opening a more effective pathway for ambient HCHO oxidation. Therefore, the Pd/TiO 2 -450R catalyst demonstrated high activity for ambient HCHO oxidation.

High temperature reduction dramatically promotes Pd/TiO2 catalyst for ambient formaldehyde oxidation

Highly dispersed iron vanadate catalyst supported on TiO2 for the selective catalytic reduction of NOx with NH3

Different amounts of silver were successfully incorporated into cryptomelane-type manganese oxide (K-OMS-2) via a one-step hydrothermal method for application in the catalytic combustion of benzene. Silver incorporation could promote the benzene oxidation performance of the catalysts. The silver doping effect was addressed in terms of the relationship between structure and activity. The prepared catalysts were characterized by ICP-OES, BET, XRD, Raman, FE-SEM, TEM, XPS, XAFS, H2-TPR and CO-TPD. The best precursor Mn/Ag mole ratio was 40. The resulting K/Ag-OMS-40 catalyst exhibited the highest activity in terms of benzene combustion and good tolerance to chlorine poisoning, all of which make it a promising candidate as an alternative to noble metal supported catalysts. All catalysts after silver incorporation maintained the structural integrity of the cryptomelane structure but with decreased crystalline size, which significantly increased the surface area and number of defects of the catalyst. The silver species, mostly in the form of Ag+, were well dispersed and partially replaced K+ in the tunnels of cryptomelane. K/Ag-OMS-40 had the largest surface area, the smallest nanorods and most abundant Mn octahedral defects. The large number of active oxygen species derived from the high Mn3+ content and Ag-O-Mn bridge bonds appeared to play critical roles in VOC decomposition.

Silver incorporated into cryptomelane-type Manganese oxide boosts the catalytic oxidation of benzene

Manganese oxides are prominent candidates for the catalytic oxidation of volatile organic compounds (VOCs) or ambient decomposition of O3 individually. Here, we compared various preparation methods...

Role of Structural Defects in MnOx Promoted by Ag Doping in the Catalytic Combustion of Volatile Organic Compounds and Ambient Decomposition of O3.

Investigation into the Enhanced Catalytic Oxidation of o-Xylene over MOF-Derived Co3O4 with Different Shapes: The Role of Surface Twofold-Coordinate Lattice Oxygen (O2f)

Hua Deng

Papers

High temperature reduction dramatically promotes Pd/TiO2 catalyst for ambient formaldehyde oxidation

Highly dispersed iron vanadate catalyst supported on TiO2 for the selective catalytic reduction of NOx with NH3

Silver incorporated into cryptomelane-type Manganese oxide boosts the catalytic oxidation of benzene

Role of Structural Defects in MnOx Promoted by Ag Doping in the Catalytic Combustion of Volatile Organic Compounds and Ambient Decomposition of O3.

Investigation into the Enhanced Catalytic Oxidation of o-Xylene over MOF-Derived Co3O4 with Different Shapes: The Role of Surface Twofold-Coordinate Lattice Oxygen (O2f)