Catalytic Combustion Of Benzene Research Articles

The effect of mass transfer on the catalytic combustion of benzene and methane over palladium catalysts supported on porous materials

Catalytic combustion of benzene and methane over palladium catalysts supported on FAU and MOR zeolites and MCM-41 and KIT-1 mesoporous materials were studied to illustrate the effect of pore size and shape of supports on their catalytic activities. The palladium catalysts supported on mesoporous materials showed high activity and a steep increase in the conversion of benzene with rising temperature. The low activity of palladium catalysts supported on FAU zeolite was ascribed to mass transfer limitation. However, conversion profiles of methane on palladium catalysts were similar, although their supports were different as zeolites and mesoporous materials. The catalytic behavior of palladium catalysts in the combustion of benzene and methane was explained by the diffusion properties of fuels in the pores of zeolites and mesoporous materials.

Catalytic combustion of benzene over supported metal oxides catalysts

Catalytic combustion of benzene over supported metal oxides has been investigated. The catalysts have been prepared by incipient wetness method and characterized by XRD, FT-Raman, ESR and TPR. Among supported metal oxides, CuOx, supported on TiO2 is found to have the highest activity for benzene oxidation. In addition, among the catalysts of copper oxide supported on TiO2, A12O3 and SiO2, titania-supported catalyst (CuOx/TiO2) gives the highest catalytic activity. CuOx/TiO2 (Cu loading 5.5 wt%) shows the total oxidation of benzene at about 250 °C. From the ESR and FT-Raman results, the CuO dispersed on the TiO2 surface acts as an active site of CuOx/TiO2 catalysts on the oxidative decomposition of benzene. The catalytic activity gradually increases with an increase of Cu loading on TiO2. When Cu loading reaches 5.5 wt%, the total conversion temperature is lowered to 300 °C. However, the catalytic activity considerably decreases at 7 wt% Cu loading. The catalytic activity increased with an increase of oxygen concentration but the concentration of benzene showed no difference in the benzene conversion. This result suggests that the rate determining step is the adsorption of oxygen.

A Mechanistic Study on the Catalytic Combustion of Benzene and Chlorobenzene

A Mechanistic Study on the Catalytic Combustion of Benzene and Chlorobenzene

A Mechanistic Study on the Catalytic Combustion of Benzene and Chlorobenzene

The catalytic combustion of benzene (C 6H 6), hexadeuterobenzene (C 6D 6), and chlorobenzene (PhCl) was investigated under various conditions on a 2 wt% Pt/γ–Al 2O 3 catalyst. Typical conditions were 1000 ppm of organics in the inflow, contact times of ∼0.3 s, and 16% O 2 in nitrogen at ∼1 bar. Benzene as such reacted very easily, much faster than PhCl per se, with T 50% only ∼145°C. With C 6H 6/C 6D 6 the kinetic isotope effect ranged from 2.5 to 1.5 between 130°C and 160°C. Cocombustion of C 6H 6/C 6D 6/PhCl led to lower rates for the benzenes but higher rates for PhCl, to give comparable T 50% values of around 250°C. Between 200°C and 300°C k H/ k D was ∼1.6. Comparable results were obtained with C 6H 6/C 6D 6/C 2Cl 4. In this case the side reaction, chlorination, is visible from formed C 6H 5Cl and C 6D 5Cl; it appears to occur without H/D isotope effect. If the O 2 concentration were increased from 8 to 14% combustion rates for C 6H 6 were increased to a limited extent; between 153°C and 213°C the order in O 2 is ∼0.2. Also the conversion of PhCl was measured at 328°C with O 2 partial pressures ranging from 1 to 16%; above 4% the conversion decreased, while the level of polychlorinated benzenes (PhCl x ) increased almost fivefold, from 0.55 to 2.5% of the PhCl input, when [O 2] was raised from 4 to 16%. Cocombustion of PhCl and heptane gave much higher rates for the former, while the output of PhCl x was greatly reduced; at 16% O 2 from 2.5% for combustion of PhCl per se, to 0.25% with 2.3 mol of heptane per mole PhCl in the feed. Water had a much less beneficial effect. The mechanism(s) are discussed on the basis of the operation of (at least) two different types of active sites. In the absence of chlorine a CH(D) bond in sorbed benzene is split, and the surface-bound H and phenyl moieties are oxidized, most likely via phenoxyl entities which are subject to rapid breakdown. Chlorine—e.g., formed from added PhCl upon its combustion—acts as a poison, the more so when using PhCl alone. Then, a slow CCl bond activation occurs on another type of site. Added heptane, through its hydrogen, can remove Cl from the metal surface and regenerate the sites for sorption and CH bond activation. The side reaction, (oxy)chlorination, is best described as recombination of a surface-bound phenyl entity with—electrophilic—chlorine, presumably at an oxidized Pt site.