Yongzhao Wang

Effect of ZrO2 promoter on the catalytic activity for CO methanation and adsorption performance of the Ni/SiO2 catalyst

The catalytic activities for CO methanation and adsorption performances of the Ni/SiO2 and Ni/ZrO2-SiO2 catalysts were investigated by a continuous flowing microreactor apparatus and in-situ diffuse reflectance Fourier transform infrared spectroscopy. The results showed that CO was completely converted at 200°C over the Ni/ZrO2-SiO2 catalyst under the reaction condition of 1% of CO, GHSV of 5000 h−1, and the atmospheric pressure. However, the CO conversion was only 35% over the Ni/SiO2 catalyst under the same reaction condition, and CO was not completely converted until 270°C, which suggested that the catalytic activity of the Ni/ZrO2-SiO2 catalyst increased with the addition of ZrO2 promoter. Meanwhile, the addition of ZrO2 promoter enhanced the CO adsorption capacity of the Ni/ZrO2-SiO2 catalyst. In the presence of H2, a large number of bridged carbonyl hydrides were formed over the Ni/ZrO2-SiO2 catalyst at lower temperatures, resulting in high catalytic activity for CO methanation. In CO methanation, the breaking of C—O bond over catalysts was by multihydrogen carbonyl hydride rather than by direct breaking.

A comparative study on the catalytic properties of high Ni-loading Ni/SiO2 and low Ni-loading Ni-Ce/SiO2 for CO methanation

Abstract Two Ni-based catalysts of 13%Ni/SiO2 (13Ni/Si) and 7%Ni-2%Ce/SiO2 (7Ni-2Ce/Si, by weight) were prepared by the incipient-wetness impregnation method and characterized with N2-sorption, XRD, H2-TPR, FT-IR, TEM, H2-TPD and CO-TPD techniques. It was shown that addition of Ce promoter generated an interaction among NiO, CeO2 and SiO2, which changed chemical environment of Ni-O-Si bond, enhanced the dispersion and reduction of NiO, and increased the active surface area. In particular, a new type of moderately strong CO adsorption sites was formed on the surface of the 7Ni-2Ce/Si catalyst. As a result, the low Ni-loading 7Ni-2Ce/Si catalyst exhibited higher CO adsorption capacity and CO methanation catalytic activity than the high Ni-loading 13Ni/Si. Under the reaction conditions of 1% CO (volume fraction in H2 atmosphere), GHSV of 7000 h−1 and atmospheric pressure, the temperature for complete conversion of CO over the 7Ni-2Ce/Si catalyst was 230°C, being 30°C lower than that found over the high Ni loading 13Ni/Si catalyst.

Effect of ammonia concentration on the catalytic activity of Pd-Cu supported on attapulgite clay prepared by ammonia evaporation in CO oxidation at room temperature

Abstract With attapulgite clay (APT) as support, the Pd-Cu/APT catalysts were prepared by an ammonia evaporation method and characterized by N2-physisorption, XRD, FT-IR, TEM and H2-TPR. The effect of ammonia concentration on the catalytic performance of Pd-Cu/APT in CO oxidation at room temperature was investigated in a fixed-bed continuous flow microreactor. The results showed that CuO appears as the main Cu species in the Pd-Cu/APT catalysts prepared with over low or over high ammonia concentration, whereas the quantity of Cu2(OH)3Cl phase is much less. However, a proper concentration of ammonia is of benefits to forming stable Cu2(OH)3Cl species in Pd-Cu/APT; owing to its high dispersion, nano-platelet morphology and strong interaction with Pd species, the presence of stable Cu2(OH)3Cl can significantly promote the catalytic performance of Pd-Cu/APT in CO oxidation. Under a gas hourly space velocity (GHSV) of 6000 h−1 for a feed stream containing 1.5% CO and 3.3% water, the Pd-Cu/APT catalyst exhibits excellent activity and stability in CO oxidation even at room temperature.

Effect of Preparation Method on the Catalytic Activities of Pd–Cu/APT Catalysts for Low-Temperature CO Oxidation

Pd–Cu/APT catalysts were prepared by an impregnation method (PC-IM) and an evaporation ammonia method (PC-AE), respectively. Their catalytic activities for low-temperature CO oxidation were studied. It is found that PC-AE shows much higher catalytic activity. Characterizations results suggest that Cu species exist as the Cu2(OH)3Cl phase with nanoplatelet morphology in PC-AE. In addition, PC-AE possesses high specific surface area and enhanced reducibility, which may contribute to the excellent catalytic ability.Graphical Abstract

Effect of precipitants on the catalytic performance of Pd–Cu/attapulgite clay catalyst for CO oxidation at room temperature and in humid circumstances

The Pd–Cu/attapulgite clay catalysts were synthesized using a deposition–precipitation method with different precipitants. The as-synthesized catalysts were characterized by ICP-AES, N2-physisorption, XRD, FT-IR, TEM and TPR. Their catalytic activities for CO oxidation were tested by a fixed-bed continuous flow reactor at room temperature and in humid circumstances. The results illustrated that the activity of CO oxidation strongly depended on the precipitant. The best catalytic performance is achieved by using NH3·H2O (PC-AH) or NH4HCO3 (PC-AHC) as precipitants. The crystalline phase of PC-AH and PC-AHC comprised of Cu2Cl(OH)3 and CuO, while the catalysts prepared with NaOH (PC-SH) or NaHCO3 (PC-SHC) as precipitants were mainly CuO. Combined with FT-IR and TEM results, it could be found that Cu2Cl(OH)3 on PC-AH and PC-AHC possessed higher stability than that on PC-SH and PC-SHC due to the different formation process and morphology of Cu2Cl(OH)3 species. The TPR results showed that the Cu2Cl(OH)3 had a strong interaction with Pd species and enhanced reducibility. Moreover, the residual sodium ions on PC-SH and PC-SHC may have adverse effect on the catalytic activity. A suitable precipitant resulted in the most efficient CO oxidation catalyst at room temperature and in humid circumstances.

Effect of ultrasonic treatment of palygorskite on the catalytic performance of Pd-Cu/palygorskite catalyst for room temperature CO oxidation in humid circumstances

ABSTRACT Pd-Cu/palygorskite catalysts were prepared by a wet impregnation method using palygorskite (PC/N-Pal) and ultrasonic-treated palygorskite (PC/U-Pal) as the support. Their catalytic activities toward CO oxidation at room temperature and in humid circumstances were investigated. PC/U-Pal exhibits much higher catalytic activity and stability than PC/N-Pal under the conditions of 1.0 vol.% CO and 3.3 vol.% H2O in the feed gas. The X-ray diffraction results indicate that quartz impurities were eliminated from the Pal after the ultrasonic treatment, and more copper species exist in the form of Cu2Cl(OH)3 in PC/U-Pal. The temperature-programmed reduction results suggest that there is an enhanced reducibility of PC/U-Pal after ultrasonic treatment. Furthermore, the ultrasonic treatment can properly decrease the hydrophilicity of the support and catalyst, which may also contribute to the excellent catalytic performance.