Confined Catalysts Application in Environmental Catalysis: Current Research Progress and Future Prospects

The work presents Pd-containing catalysts for practical application with enhanced low-temperature activity in the complete oxidation of volatile organic compounds (VOCs) using innovative combinations of reduced graphene oxide (RGO) and alumina. The catalysts were characterized by XRD, SEM, TEM, XPS, low-temperature N2-adsorption, and CO chemisorption. The tests on complete catalytic oxidation of different VOC (propane, butane, hexane, dimethyl ether, toluene, propylene) and CO were carried out. The reaction kinetics and the mechanism of the reaction of complete oxidation of toluene are being investigated in detail. The results show that the new catalyst design makes it able to completely oxidize the studied VOCs and CO at low temperatures (100–350 °C) with long-term stability. Using a variety of instrumental methods, it was established that for high activity and long-term stability, the optimal ratio Pd/PdO should be close to 1:1. The most probable mechanism of complete toluene oxidation is the mechanism of Langmuir–Hinshelwood. The high activity and the weak effect of water on the catalyst performance leads to further perspectives for the application of the currently developed approach for the preparation of large-scale monolithic catalytic systems for air pollution control.

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

General study of catalytic oxidation of various VOCs over La0.8Sr0.2MnO3+x perovskite catalyst—influence of mixture

The emission of gaseous pollutants from the combustion of fossil fuels is believed to be one of the most serious environmental challenges in the 21st century. Given the increasing demands of multipollutant control (MPC) via adsorption or catalysis technologies, such as NOx, volatile organic compounds (VOCs), heavy metals (Hg etc.), and ammonia, and considering investment costs and site space, the use of existing equipment, especially the selective catalytic reduction (SCR) system to convert pollutants into harmless or readily adsorbed substances, is one of the most practical approaches. Consequently, many efforts have been directed at achieving the simultaneous elimination of multipollutants in a SCR convertor, and this method has been widely used to mitigate the stationary emission of NOx. However, the development of active, selective, stable, and multifunctional catalysts/adsorbents suitable for large-scale commercialization remains challenging. Herein, we summarize recent works on the applications of SCR in MPC, describing the approaches of (i) SCR + VOCs oxidation, (ii) SCR + heavy metal control, and (iii) SCR + NH3 reduction to reveal that the efficiency of simultaneous elimination depends on catalyst composition and flue gas parameters. Furthermore, the synergistic promotional/inhibitory effects between SCR and VOCs/ammonia/heavy metal oxidations are shown to be the key to the feasibility of the reactions.

Theoretical study on photocatalytic oxidation of VOCs using nano-TiO 2 photocatalyst

Ultrathin Co(3)O(4) nanostructures with high catalytic oxidation of CO were synthesized by heating cobalt foils under atmospheric conditions. The Co(3)O(4) nanostructures were selectively exposing (111) planes composed of plenty of Co(3+) cations. We observed ultrahigh catalytic oxidation of CO in Co(3)O(4) nanowires with about 3 nm diameter.

2 与H 2 O的表面反应.特别是后两个步骤涉及的 动力学过程(电荷分离/转移和表面反应)往往是限制光

The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds

Cerium–titanium mixed oxides and mesoporous cerium-modified titanium and cerium-modified titanium–zirconium mixed oxides were synthesized in order to obtain active support for gold volatile organic compound (VOC) oxidation catalysts. Ce–Ti mixed oxides were synthesized by sol–gel method. Mesoporous TiO2 and Ti–Zr mixed oxides were prepared through the surfactant templating technique. Gold was loaded on supports by deposition-precipitation method. The catalysts were characterized by thermal analysis, XRD, N2 analysis, TPR, DR/UV–vis and IR. The results evidenced the beneficial role of ceria modifying additive in decreasing the degree of crystallinity of mesoporous support and its particle size. A high degree of synergistic interaction between ceria and mesoporous oxide was observed. H2-TPR revealed that the reducibility of the catalysts is greatly enhanced in the presence of gold. Considering the light off temperature, the activity of Au/mesoporous cerium-modified titanium oxide is particularly interesting for VOC oxidation comparatively to the same catalysts with a classical support. The gold particles would be more dispersed and stable. However, the sample Au/mesoporous cerium-modified titanium–zirconium mixed oxide is less interesting for VOC oxidation, particularly for toluene oxidation whose activity depends essentially on the adsorption of toluene molecule.

Assessing the contribution of VOCs to SOA formation and identifying their key species during ozone pollution episodes in a typical petrochemical city.

The main part of the VOCs (volatile organic compounds) contained in diesel exhaust (≈80%) is oxidized to CO and CO2 over an SCR (selective catalytic reduction) catalyst. CO is the major product of this oxidation, representing about 50−70% of the formed products (CO + CO2). This preferential formation of CO leads to a pronounced increase of CO emissions when an SCR process is added to a diesel engine. A small fraction of the VOCs is selectively oxidized to carboxylic acids over the SCR catalyst. This selectivity is due to the acidic properties of the catalyst causing the preferential desorption at the oxidation state of the acid. The main products of these oxidation reactions are the lower monocarboxylic acids and some dicarboxylic acids forming stable anhydrides, especially maleic and phthalic acid. The highest emissions of these acids are found at low temperatures; they decrease at higher temperatures. Formic acid is preferentially decomposed into carbon monoxide and water. It must therefore be assumed that the strong increase of CO mentioned above is due to a mechanism involving the thermal decomposition of formic acid formed from various primary VOCs.

The catalytic oxidation of carbon monoxide on cobalt oxide

Origins of catalysis for CO oxidation on porous Ag fabricated by leaching of intermetallic compound Mg3Ag

The mechanism of the catalytic oxidation of CO activated by MoS2-supported Au19 nanoparticles (NPs) was studied using density functional theory calculations. Of particular interest were the effects of the physical/chemical modification of a MoS2 support on the CO oxidation pathway and the activation of specific reactive centers, i.e., the Au atoms of Au19 or the Au-MoS2 perimeter sites. We systematically modified MoS2 by introducing an S vacancy or 5% tensile strain and studied the shift of each reaction step and the overall change in the reaction pathway and activity. Despite the lack of direct involvement of the Au-MoS2 perimeter in the reaction, the combination of an S vacancy and the tensile strain in the MoS2 support was found to improve the stability and catalytic activity of Au NPs for CO oxidation. The results show that support modification can provide information for new pathways for the rational design of Au-based catalysts.

Effect of composition and morphology on the catalytic activity in CO oxidation of Co-, Cu-, Ce-containing oxide materials prepared by citrate method has been studied. It was shown that composites consist of well-dispersed oxides Со3O4, CuO and CeO2 with average crystallite sizes 13–24 nm, 14–26 nm and 3–7 nm, respectively. It was established that Co-, Cu-, Ce-oxide nanocomposites demonstrated higher catalytic activity in CO oxidation in comparison with individual oxides. The ternary oxide system Со3O4–CuO–СеO2 (Со:Cu:Се=10:1:1) was found to possess the highest catalytic activity due to formation finely dispersed particles of CuO and СеO2 oxides simultaneously with nanosized Со3O4 species and formation of large quantity of mobile oxygen at the interfaces between the oxide nanoparticles.