Low-Temperature Ammonia Oxidation in a Microchannel Reactor with Wall-Loaded X(X = Pt, Pd, Rh, PtPdRh)/TiO2 Nanotube Catalysts

Highly effective electrocatalytic reduction of N-nitrosodimethylamine on Ru/CNT catalyst

N-Nitrosodimethylamine (NDMA) is a commonly identified carcinogenic and genotoxic pollutant in water. In this study, we prepared Ru catalysts supported on carbon nanotube (Ru/CNT) and studied the electrocatalytic reduction of N-nitrosamines on Ru/CNT electrode in a three-electrode system. The results show that Ru-based catalyst exhibits a high activity of 793.3 μmol L^-1 gCat^-1 h^-1 for electrochemical reduction of NDMA. Reaction mechanism study discloses that the electrocatalytic reduction of NDMA is accomplished by both direct electron reduction and atomic H* mediated indirect reduction pathways. Further product analysis indicates that NDMA is finally reduced to dimethylamine (DMA) and ammonia. The reduction efficiency of NDMA strongly relies on cathode potential, initial NDMA concentration and solution pH. To verify the universality of Ru/CNT electrode, electrocatalytic reduction of three dialkyl N-nitrosamines with different alkyl groups was performed and Ru catalyst has high catalytic activities for the three N-nitrosamines, while the catalytic efficiency differs with their structures. Simultaneous electrochemical reduction of the three N-nitrosamines indicates that the reduction rates of N-nitrosamines follow the same order in the multiple-component system as that in the single-component system. Catalyst recycling results demonstrate that after 5 consecutive recycling runs Ru/CNT electrode remains almost identical catalytic activity to the fresh catalyst, manifesting the high catalytic stability of Ru/CNT electrode.

Continuous-Flow Ammoxidation of 2-Methylpyrazine to 2-Cyanopyrazine with High Space-Time Yield in a Microreactor

A microreactor (MR) with a vaporization microchamber and a sinusoidal wave microchannel was fabricated to synthesize 2-cyanopyrazine (CP) directly with an aqueous 2-methylpyrazine (MP) solution. A continuous-flow process with high space-time yield was achieved under the premise of strong exothermality of this ammoxidation reaction. The vanadium metal oxide catalysts with four different supports (α-Al₂O₃, γ-Al₂O₃, ZSM-5(50), ZSM-5(80)) were evaluated by simply stacking in the wave microchannel from 350 to 540 °C. The process parameters (temperature, reactant ratio, and size of catalysts) were optimized with the selected CrVPO/γ-Al₂O₃ catalyst, and an optimal ammoxidation process with MP conversion (X _MP) of 71.5% and CP selectivity (S _CP) of 93.7% was obtained by a volume space velocity (GHSV) of 13 081 h^-1 at 480 °C. Correspondingly, the space-time yield of CP (STY_CP) was 1724-77 082 g_CPkg_cat ^-1h^-1, which was the highest value ever reported for this reaction. Meanwhile, the ammoxidation reaction showed a great continuous-synthesis stability of 50-h running in the microreactor with the CP yield (Y _CP) remaining 56%-68%.