Qinghua Yan

Synthesis of Pt doped Mg–Al layered double oxide/graphene oxide hybrid as novel NOx storage–reduction catalyst

We report the synthesis of Pt doped Mg–Al layered double oxide/graphene oxide (Pt–LDO/GO) hybrid as novel NOx storage and reduction (NSR) catalyst. For the preparation of layered double hydroxide/GO hybrids, LDHs and graphite oxide were first exfoliated into single-layers, followed by self-assembly. LDO/GO hybrids were obtained by thermal treatment of LDH/GO. The obtained LDH/GO and LDO/GO hybrids were thoroughly characterized using XRD, SEM, TEM, FT-IR, and BET analyses. Then the NOx storage capacity of neat LDO and LDO(10)/GO hybrids were compared by isothermal NOx adsorption tests. The influence of adsorption temperature, gas flow, calcination temperature, and LDH dispersion concentration were systematically studied. The results demonstrated that the NOx storage capacity of neat LDO was significantly improved from 0.175 to 0.314 mmol g−1 by introducing only 7 wt% of GO, which could be attributed to the enhanced particle dispersion and stabilization. Moreover, the NOx storage capacity of the hybrid could be further increased close to 0.335 mmol g−1 catalyst by doping with 2 wt% Pt. The Pt–LDO(1)/GO also exhibited excellent lean-rich cycling performance, with an overall 71.7% of NOx removal. This work provided a new scheme for the preparation of highly dispersed LDH/GO hybrid type NSR catalyst.

Synthesis of Pt/K 2 CO 3 /MgAlO x –reduced graphene oxide hybrids as promising NO x storage–reduction catalysts with superior catalytic performance

Pt/K2CO3/MgAlOx–reduced graphene oxide (Pt/K/MgAlOx–rGO) hybrids were synthesized, characterized and tested as a promising NOx storage and reduction (NSR) catalyst. Mg–Al layered double hydroxides (LDHs) were grown on rGO via in situ hydrothermal crystallization. The structure and morphology of samples were thoroughly characterized using various techniques. Isothermal NOx adsorption tests indicated that MgAlOx–rGO hybrid exhibited better NOx trapping performance than MgAlOx, from 0.44 to 0.61 mmol · g−1, which can be attributed to the enhanced particle dispersion and stabilization. In addition, a series of MgAlOx–rGO loaded with 2 wt% Pt and different loadings (5, 10, 15, and 20 wt%) of K2CO3 (denoted as Pt/K/MgAlOx–rGO) were obtained by sequential impregnation. The influence of 5% H2O on the NOx storage capacity of MgAlOx–rGO loaded with 2 wt% Pt and 10% K2CO3 (2Pt/10 K/MgAlOx–rGO) catalyst was also evaluated. In all, the 2Pt/10 K/MgAlOx–rGO catalyst not only exhibited high thermal stability and NOx storage capacity of 1.12 mmol · g−1, but also possessed excellent H2O resistance and lean–rich cycling performance, with an overall 78.4% of NOx removal. This work provided a new scheme for the preparation of highly dispersed MgAlOx–rGO hybrid based NSR catalysts.

Synthesis of Cu0.5Mg1.5Mn0.5Al0.5Ox mixed oxide from layered double hydroxide precursor as highly efficient catalyst for low-temperature selective catalytic reduction of NOx with NH3

We report a novel NH3-SCR catalyst Cu0.5Mg1.5Mn0.5Al0.5Ox synthesized from layered double hydroxides with superior activity in a wide temperature range and improved SO2 and H2O resistance comparing to conventional doped Mn/γ-Al2O3. This catalyst results in a high NOx removal efficiency of 87.0-96.6% in the low temperature range of 100-250 °C, much better than Mn/γ-Al2O3 (35.0-67.2%). Besides, it exhibits significant resistance to SO2 and H2O due to the existence of Cu and Mg. The promoting effects of Cu and Mg are thoroughly investigated using various physico-chemical techniques. The superior NH3-SCR activity of Cu0.5Mg1.5Mn0.5Al0.5Ox catalyst can be associated with its high specific surface area, high reducibility of MnO2 and CuO species, abundance of acid sites, and the well dispersion of MnO2 and CuO species. The interactions between SO2 and NH3, and the degradation mechanism caused by SO2 were investigated using in-situ DRIFT analysis.