Cordierite and citric acid regulate crystal structure of manganese oxide for effective selective catalytic reduction of nitrogen oxide.

Catalyst is the key to effective selective catalytic reduction of nitrogen oxide, and developing catalyst is always one of the hottest topics in both field of industry and academy. In order to realize an industrial application, one catalyst must grow on a specific support. However, seldom work compared the difference of catalyst growth with or without support. In this work, Mn2+ growth on cordierite (a typical commercial catalyst support) was investigated. The formed active species were detailedly characterized. As a result, orthorhombic cordierite guided Mn2+ to form orthorhombic oxide (γ-MnO2). In comparison, Mn2+ preferred to form tetragonal ß-MnO2 without the guide of cordierite. During the synthesis, cordierite and citric acid promoted γ-MnO2 dispersion, increased growth of exposed (301) facet, and created lattice distortion between (301) and (101) planes. ß-MnO2 mainly exposed (101) facet. The best catalyst was γ-MnO2, which was mostly dominated by (301) facet and had an obvious lattice distortion from 75° to 78° between (301) and (101) planes. In comparison, 0.1 g of the γ-MnO2 reached a catalytic conversion rate 1.6 times bigger than 1.0 g of ß-MnO2 at 250 °C. This work helps to understand guiding effect of support on formed catalytic species, which is in favor of developing effective commercial catalysts for environmental pollutants.

Electroplating sludge-derived metal and sulfur co-doping catalyst and its application in methanol production by CO2 catalytic hydrogenation.

Electroplating sludge is a hazardous waste and its recycling is a hot topic. Electroplating sludge usually contains plenty of transition metals and multi-hetero atoms, which are potential resources. For the first time, this work synthesized spinel catalyst from Zn- and Cr-containing electroplating sludges by a simple calcination method, and applied the obtained catalysts in CH3OH production by CO2 catalytic hydrogenation. The spinel was doped by various heteroatoms, including Fe, Mn, Cu, and even S. According to detailed characterizations, the metal doping increased the low-temperature conversion efficiency of CO2 but decreased the CH3OH selectivity at the same time. After a further doping of S, although CO2 conversion efficiency was slightly decreased, the selectivity of CH3OH was significantly increased. After all, the optimized catalyst attained a conversion efficiency of 8.6% (CO2) as well as a selectivity of 73.3% (CH3OH) at 250 °C and 3 MPa. As a result, above results realized high-value-added utilization of hazardous waste and producing valuable product at the same time, which was in favor of circular development.

Ball milling transformed electroplating sludges with different components to spinels for stable electrocatalytic ammonia production under ambient conditions.

Electroplating sludge is classified as hazardous waste, but it is also a potential raw resource since it contains plenty of transition metals. However, the component of electroplating sludge is unstable, which hinders recycling. This work investigates the possibility to synthesize spinels with stable catalytic performances by different electroplating sludges. The obtained catalysts are used in electrocatalytic N2 reduction to produce ammonia. As a result, CuCr2O4, ZnCr2O4, and NiCr2O4 spinels are successfully synthesized by a ball-milling and calcination method. These spinels result in ammonia yields of 7.30-8.86 µg h-1 mg-1cat. Among the three spinels, CuCr2O4 shows the highest yield of 8.86 µg h-1 mg-1cat at -0.9 V. Its faradaic efficiency reaches 0.57%. In addition, no by-product N2H4 is detected, indicating a high selectivity. The catalytic process is carried out by both distal and alternating pathways, in which metal doping and oxygen vacancy function as binding sites for N2 adsorption and reduction. Above results indicate that electroplating sludges with unstable components are feasible to produce spinels for stable electrocatalytic ammonia production under ambient temperature. This is in favor of high-value-added utilization of hazardous waste, and devotes to circular economy.