Catalytic steam reforming of chlorocarbons: catalyst comparisons

Catalyst candidates for steam reforming chlorocarbons have been screened for activity using methyl chloride as a model reactant. At 500 degrees C, a H2O/C ratio of about 10 and a GHSV of 254 000 h(-1), catalysts comprising 0.5% loading of the metals on gamma-Al2O3 resulted in three groups: extremely high conversions (Pt, Rh, Pd), moderate conversions (Cu, Re, Ir) and low conversions (Ru, Ni, Co). At high conversions (>0.998), the selectivity towards the water gas shift reaction was high for Pt and low for Rh and Pd. However, shift activity declined for all catalysts upon continuous exposure to chlorine compounds. Hydrogenolysis of CH3Cl was also detected by the presence of CH4 and activity increased in the order Ru, Pt and Pd but all were less than Ni. Conversion of CH3Cl over Pt follow first-order kinetics, with a rate constant that follows the Arrhenius equation over a wide temperature range. Product compositions support a reaction network in which a consecutive steam reforming-water gas shift sequence occurs in parallel hydrogenolysis. The qualitative dependence of these reactions on process conditions were studied and it was found that shift and hydrogenolysis activities decreased as the temperature increased but increased with high concentrations of CH3Cl. Platinum was equally effective for the conversion of CH3CCl3, CHClCCl2, and CCl2CCl2, except that no hydrogenolysis was detected. Extremely high levels of destruction (>0.99999) were maintained for periods over 20 h without carbon formation or catalyst deactivation other than a progressive loss of shift activity. (C) 1999 Elsevier Science B.V. All rights reserved.