Methylene chloride oxidation on oxidative carbon-supported chromium oxide catalyst

Several carbon-supported chromium oxide catalysts were prepared by varying the textural and surface properties of the support. Reactor experiments were carried out in a fixed bed reactor at a temperature ranging from 100 to 400°C and a space velocity of 12,000h^-1 at atmospheric pressure. Our reaction conditions are limited below 400°C to prevent burn-off of support. The support and catalyst characteristics, including surface area, acidity, surface composition, oxygen pick-up and oxidation state of chromium cation, were measured and compared. N₂ adsorption studies demonstrated that the oxidation process of the support increased the micropore volume and the mesopore surface area. Oxidizing of the original carbon led to an increase in the concentration of surface oxygen groups and a change in their distribution as determined by TPD. XPS results showed that the quantities of carboxyl groups increased with oxidative treatment, indicating that the acidic properties of the carbon were enhanced, in agreement with pH analysis and TPD results. XPS results of catalysts showed that the creation of an acidic surface having less thermally stable carboxyl group with oxidative treatment of activated carbon helped the high valence of chromium ion on the catalyst. The oxygen chemisorption experiment showed that high valence of chromium cations on activated carbon provided more adsorption sites and therefore led to the higher activity of this catalyst. Catalytic results indicated that carbon-supported chromium oxide catalysts were effective for complete oxidation of CH ₂Cl₂. Oxidative treatment of the support increased its acidity and therefore led to improved activity by highly dispersed Cr ⁶⁺ species on catalysts.