Surface structure of bulk nickel catalysts, active in the gas-phase hydrodechlorination reaction of aromatics

Abstract

Several bulk nickel catalysts obtained from different procedures have been structurally characterized using BET, XRD, SEM, TPR and TPD techniques. XRD and SEM clearly show diffentiated crystalline morphologies on the oxidized and reduced nickel phases obtained from the three catalysts studied, in agreement with the BET surface areas. TPR and TPD results show the reducibility behaviour, and that mainly atomic hydrogen chemisorbs onto the catalysts with the better crystallized and larger nickel crystallites. The catalytic activities depicted by this study for the hydrodechlorination reaction of ortho-dichlorobenzene show that all the bulk nickel catalysts tested yield conversions and selectivities towards benzene of >80% at temperatures >493 K. Also, the catalysts with larger octahedral crystallites showed higher TOF values and selectivities toward benzene than those with poorly crystallized structures at any reaction temperature in the range 523–393 K. The behaviour is interpreted in terms of a structure-sensitive reaction. Also, a reversible/irreversible temperature-dependent mechanism of nickel chloride formation is proposed.