Search

1,2-dichloroethane (1,2-DCE) is a representative industrial chlorinated volatile organic compound (CVOC) making great hazardous to the environment and human health. In this work, LaSrMnCoO6 (LSMC) double perovskite-type materials with high thermal stability and coke resistance in 1,2-DCE oxidation were prepared by a facile sol-gel method. Based on this, a series of CrOx/LaSrMnCoO6 catalysts (Cr/LSMC, CrOx loading = 5 to 20 wt.%) which combine the merits of CrOx (high activity and chlorine tolerance) and LaSrMnCoO6 were synthesized and adopted in deep oxidation of 1,2-DCE for the first time. As expected, obvious synergistic effects between CrOx and LSMC on 1,2-DCE destruction were observed. Amongst, 10 wt.% CrOx/LaSrMnCoO6 (10Cr/LSMC) shows the best catalytic activity with 90% of 1,2-DCE destructed at 400 °C. Furthermore, the outstanding catalytic durability and water resistance of 10Cr/LSMC in 1,2-DCE oxidation were also demonstrated. In addition to this, the reaction pathway of 1,2-DCE decomposition over Cr/LSMC materials was discussed based on the results of online product analysis. We found that the enhanced catalytic performance of Cr/LSMC materials can be reasonably attributed to their high reducibility, excellent 1,2-DCE adsorption capability, and large amounts of surface active lattice oxygen species. It can be anticipated that the Cr/LSMC catalysts are promising materials for CVOC elimination and the results from this work could also provide some new insights into the design of catalysts for CVOC efficient destruction.

A series of Sm-modified MnOx-TiO2 (SMT) catalysts are prepared and characterized. The results show that the introduction of Sm can effectively restrain the crystallization process of MnOx and TiO2, enhance the specific surface area, increase the surface concentration of chemisorbed oxygen species and the amount of strong surface acid sites, and reduce the surface concentration of Mn4+. The catalytic performances of the SMT catalysts are evaluated by the selective catalytic reduction (SCR) of NOx with NH3. It is found that SMT-0.3 catalyst (a 0.3 mol rate of Sm/Mn) exhibits a 100% NOx conversion in a wide operating temperature window from 180 to 390 °C, and a 100% N2 selectivity from 120 to 390 °C under a GHSV of 36,000 h−1, which is obviously better than MnOx-TiO2 without Sm addition. In-situ DRIFT spectra reveal that, at low temperature (below 200 °C), absorbed NH3 species can react with gas-phase NO over MnOx-TiO2 catalyst following Eley-Rideal (E-R) mechanism, while the NH3-SCR of NO over SMT-0.3 follows both E-R and Langmuir-Hinshelwood (L-H) mechanisms. However, at high temperature (above 200 °C), the SCR reaction over MnOx-TiO2 is via “standard SCR” process, but the SCR reaction over SMT-0.3 is through “fast SCR” reaction.

A series of NiyCo1-yMn2Ox microspheres (MSs) (y = 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized successfully by a hydrothermal method. Their physicochemical properties of the as-prepared NiyCo1-yMn2Ox MSs were explored by using a series of characterizations, and their catalytic performances were evaluated by the selective catalytic reduction (SCR) of NOx with NH3. It was found that there are the synergetic effects between Ni and Co, which have an important impact on the surface physicochemical properties of NiyCo1-yMn2Ox MSs, such as the roughness of the surface, the stacking molding, the crystal structure, the specific surface area, the concentrations of surface Mn4+, Co3+ and Ni2+, the reducibility, and the proportion of weak acid and strong acid sites, etc, which further affect the reaction mechanism of de-NOx of NiyCo1-yMn2Ox MSs, and finally dominate their catalytic performances for the SCR of NOx with NH3. Among all NiyCo1-yMn2Ox MSs, Ni0.7Co0.3Mn2Ox exhibits the optimal catalytic performance for the SCR of NOx, which is much better than CoMn2Ox and NiMn2Ox. This work may shed light on the deliberately designed Mn-based SCR catalysts with high activity by taking advantage of the synergetic effects between components.

Selective catalytic reduction (SCR) technology has been widely used for the removal of NOx from flue gas. However, it is still a challenge to develop novel low-temperature catalysts for SCR of NOx, especially at temperatures below 200 °C. This paper reviewed the recent progress on the Mn-based catalysts for low-temperature SCR de-NOx with NH3. Catalysts were divided into four categories, single MnOx, Mn-based multi-metal oxide, Mn-based multi-metal oxide with support, and Mn-based monolith catalyst. In the section of single MnOx, the effects of several factors, such as Mn oxidation state, crystallization state, specific surface area and morphology on catalytic activity were systematically reviewed. In the section of multi-metal oxide catalysts, the various roles played by the components of catalysts were intentionally summarized from four aspects, improving de-NOx efficiency, enhancing N2 selectivity, improving resistance to SO2 and H2O, extending operation temperature window, respectively. Moreover, the newly emerging morphology-dependent nanocatalysts were highlighted at the end of this section. In the introduction of supported metal oxide catalysts, the effects of supports were systematically analyzed according to their types, such as Al2O3, TiO2, carbon materials, etc. Considering the actual operation, Mn-based monolith catalysts were also introduced with regard to monolith supports, such as ceramics, metal wire mesh, etc. Subsequently, NH3-SCR mechanisms at low temperature, including E-R and L-H mechanisms, were discussed. At last, the perspective and the future direction of low-temperature SCR of NOx were proposed.

A new type of Eu, N-codoped mesoporous TiO2 microspheres with yolk-shell structure (TiO2@void@TiO2) was successfully synthesized by a facile one-pot hydrothermal method at low temperature (180 C). The physical and chemical properties of as-synthesized samples, such as morphology, crystal phase, surface elements composition, porous structure, specific surface area and optical response, were characterized in detail. The resultant samples were porous microspheres with a diameter of about 1-3 mu m, and were composed of a large number of smaller nanoparticles. An interior circular cavity in each microsphere was formed between core and shell to construct a special yolk-shell structure, and a large number of pores were produced in shell and yolk by CO2 gas bubbles resulting from hydrothermal decomposition of the urea molecules, which tremendously increased the specific surface area and the pore volume of as-obtained samples. The absorption edges of Eu, N-codoped TiO2 were extended to longer wavelength, which led to notable absorption in the visible-light region. The photocatalytic performances of all samples were evaluated by photocatalytic decoloration of rhodamine B and methyl orange under visible light irradiation (lambda > 420 nm). Eu, N-codoped TiO2 with 0.1 at.% Eu dopant showed the highest photocatalytic activity, the efficiency of which was 5 times higher than that of Degussa P25. The enhanced photocatalytic performance could be attributed to the synergic effects of many factors, such as high specific surface area, large pore volume and strong absorption to visible light, which were created by the Eu, N-codoping and the unique yolk-shell structure. Based on the above results, the mechanism of enhanced photocatalysis on Eu, N-codoped TiO2 under visible light was proposed. (c) 2012 Elsevier B.V. All rights reserved.