Novel amorphous Ni-B catalysts supported on alumina have been developed for the production of hydrogen peroxide from carbon monoxide, water and oxygen. The experimental investigation confirmed that the promoter/Ni ratio and the preparation conditions have a significant effect on the activity and lifetime of the catalyst. Among all the catalysts tested, the Ni-La-B/γ- Al2O3 catalyst with a 1:15 atomic ratio of La/Ni, dried at 120℃, shows the best activity and lifetime for the production of hydrogen peroxide. The deactivation of the alumina-supported Ni-B amorphous catalyst was also studied. According to the characterizations of the fresh and used catalysts by SEM, XRD and XPS, no sintering of the active component and crystallization of the amorphous species were observed. However, it is water poisoning that leads to the deactivation of the catalyst. The catalyst characterization demonstrated that the active component had changed (i.e., amorphous NiO to amorphous Ni(OH)2) and then salt was formed in the reaction conditions. Water promoted the deactivation because the surface transformation of the active Ni species was accelerated by forming Ni(OH)2 in the presence of water. The formed Ni(OH)2 would partially change to Ni3(PO4)2.

The combination of catalyst and non-thermal plasmas has led to some unusual chemical behaviors, especially with zeolite catalyst. A mechanism has been proposed to explain the observed interaction between catalyst and non-thermal plasmas. This mechanism includes two aspects: plasma promoted or induced catalysis and catalyst enhanced non-equilibrium of nonthermal plasmas. In this paper, we present some direct experimental evidence for the catalyst (zeolite)-enhanced non-equilibrium of non-thermal plasmas suggesting the use of zeolite increases, significantly, the electron temperature of non-thermal plasmas, while the gas temperature remains unchanged. A floating double-probe characteristic has been utilized to measure the electron temperature. Compared to the case without zeolite, the electron temperature of non-thermal plasmas with Mo-Zn/HZSM-5 increases up to 250%, while, at the same time, the discharge power reduces 58%, compared to that without zeolite. r 2002 Elsevier Science B.V. All rights reserved.

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In this work, a novel glow discharge plasma treatment of Pd/HZSM-5 catalyst, followed by calcination thermally, has been conducted. Such prepared catalyst presents a higher catalytic activity and an enhanced stability over the catalyst prepared without plasma treatment. The methane conversion over the plasma treated catalyst is close to 100% at 450℃, but it is only ca. 50% at the same temperature over the catalyst without plasma treatment. The XPS, H2 chemisorption and XRD characterizations confirm an enhanced dispersion has been achieved with the plasma reduction (during treatment) followed by oxidation (during calcination). Upon FT-IR analyses, the plasma treatment, followed by calcination thermally, also leads to enhanced Brönsted and Lewis acidities. The amount of Brönsted acid sites of the plasma treated Pd/HZSM-5 catalyst is 1.13 times larger than that of the catalyst without plasma treatment, while the amount of Lewis acid sites of the plasma treated Pd/HZSM-5 catalyst is 1.21 times higher. The enhanced acidities are definitely helpful to increase the dispersion of PdO over the support and improve the interaction between PdO and HZSM-5 support, which leads to a remarkable improvement in the catalyst stability.

In this work, a direct conversion of methane in the presence of carbon dioxide using dielectricbarrier discharge plasmas has been conducted. The product includes syngas (H2 and CO), gaseous hydrocarbons (C2 to C5), liquid hydrocarbons (C5 to C11+), and oxygenates. The liquid hydrocarbons are highly branched, representing a high octane number, while the oxygenates mainly consist of series of alcohols and acids. A detailed analysis of product distribution has been performed under variable feed conditions with different reactor configurations. At the high CH4/CO2 feed ratio, the wider discharge gap (1.8mm) is more favored for the formation of methanol and ethanol. For the production of acetic acid, the narrower discharge gap (1.1mm) is better, especially, with the existence of after-glow zones. Conditions favored for the production of acetic acid are also good for the production of liquid fuels.