Ben W.-L. Jang

Catalyst preparation using plasma technologies

This paper discusses catalyst preparation using thermal and cold plasmas. In general, there are three main trends in preparing catalysts using plasma technologies: (1) plasma chemical synthesis of ultrafine particle catalysts; (2) plasma assisted deposition of catalytically active compounds on various carriers, especially plasma spraying for the preparation of supported catalysts; (3) plasma enhanced preparation or plasma modification of catalysts. Compared to conventional catalyst preparation, there are several advantages of using plasmas, including: (1) a highly distributed active species; (2) reduced energy requirements; (3) enhanced catalyst activation, selectivity, and lifetime; (4) shortened preparation time. These advantages are leading to many potential applications of plasma prepared catalysts.

Enhanced effect of water vapor on complete oxidation of formaldehyde in air with ozone over MnOx catalysts at room temperature.

At room temperature, the enhanced effect of water vapor on ozone catalytic oxidation (OZCO) of formaldehyde to CO2 over MnOx catalysts and the reaction stability was reported. In a dry air stream, only below 20% of formaldehyde could be oxidized into CO2 by O3. In humid air streams (RH≥55%), ∼100% of formaldehyde were oxidized into CO2 by O3 and the reaction stability was significantly enhanced. Meanwhile, in situ Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra of OZCO of HCHO demonstrate that the amount of both monodentate and bidentate carbonate species on MnOx, in the dry stream, increased gradually with time on stream (TOS). However, in the humid stream, almost no accumulation of carbonate species on the catalysts was observed. To clarify the enhanced mechanism, formaldehyde surface reactions and CO2 adsorption/desorption on the fresh, O3 and O3+H2O treated MnOx catalysts were examined comparatively.

Promotional effect of Pd single atoms on Au nanoparticles supported on silica for the selective hydrogenation of acetylene in excess ethylene

A Pd single-atom alloy (SAA) structure was constructed by alloying Pd with Au supported on silica. The XRD and HRTEM results demonstrated that the addition of a small amount of Pd efficiently prevented the sintering of Au nanoparticles. The DRIFTS and EXAFS results confirmed that the Pd SAA structure was formed when the atomic ratios of Pd/Au were lower than 0.025. The Pd SAA structure exhibits a much better catalytic performance for the selective hydrogenation of acetylene in excess ethylene than the corresponding monometallic Au or Pd systems.

Ozone catalytic oxidation of adsorbed benzene over AgMn/HZSM-5 catalysts at room temperature

To provide insight into the mechanism of plasma catalytic oxidation of adsorbed benzene in a cycled storage–discharge (CSD) plasma catalytic process, ozone catalytic oxidation (OZCO) of adsorbed benzene over the AgMn/HZSM-5 (AgMn/HZ) catalyst at room temperature was studied. The properties of the AgMn/HZ catalyst were compared with those of HZ, Mn/HZ, Ag/HZ catalysts in investigations of the TPD of adsorbed benzene, the product distribution and O3 decomposition in OZCO of adsorbed benzene, and TPO and TPD of the used catalysts. For the AgMn/HZ catalyst, the adsorption capacity and the adsorption strength of benzene were significantly improved as compared to HZ, Ag/HZ and Mn/HZ. Adsorbed benzene is oxidized completely to CO2 by O3 catalyzed by Ag on HZ. MnOx, on the other hand, further speeds up the OZCO rate of benzene adsorbed on Ag/HZ.

Ozone catalytic oxidation for ammonia removal from simulated air at room temperature

Ozone catalytic oxidation (OZCO) for removing ammonia from simulated air over the AgMn/HZSM-5 (AgMn/HZ) catalyst with high ammonia conversion and high N2 selectivity at room temperature is reported for the first time. HZ, Ag/HZ, Mn/HZ and AgMn/HZ catalysts were compared in the OZCO reactions of gaseous and adsorbed NH3. In OZCO of gaseous NH3, N2 was the major product and N2O was the minor product. NH3 conversion dropped quickly with time-on-stream (TOS) over HZ and Ag/HZ catalysts while it remained almost constant at a high level over Mn/HZ and AgMn/HZ catalysts during the entire test. N2 selectivity of the AgMn/HZ catalyst was higher than that of the Mn/HZ catalyst. When the initial concentration of NH3 was 521 ppmv and the ratio of initial concentration of O3 to NH3 was 1.73, 99% NH3 conversion with 94% N2 selectivity was obtained over the AgMn/HZ catalyst at room temperature and 150 000 ml g−1 h−1 gas hourly space velocity (GHSV). Finally, the pathways for OZCO of NH3 were proposed for the four catalysts based on the comparative investigation of the gaseous products and surface species during OZCO of adsorbed and gaseous NH3.