S. Asplund et al., CATALYST DEACTIVATION IN LIQUID-PHASE AND GAS-PHASE HYDROGENATION OF ACETYLENE USING A MONOLITHIC CATALYST REACTOR, Catalysis today, 24(1-2), 1995, pp. 181-187
The deactivation of a monolithic Pd/alpha-alumina catalyst in the sele
ctive hydrogenation of acetylene in the presence of excess ethylene ha
s been studied. The deactivation behavior of the monolithic catalyst i
n the gas-phase hydrogenation was compared to that of the liquid-phase
hydrogenation. It was shown that the deactivation behavior was differ
ent in the two systems. It was concluded that in the gas-phase hydroge
nation the rate of the deactivation is strongly dependent on the opera
ting conditions. In the liquid-phase hydrogenation, both the catalytic
activity and the ethylene selectivity declined during the first 60 h
of operation and then stabilized. This was not observed in the gas pha
se. Here, the activity and the selectivity passed through a maximum. T
emperature programmed analyses of spent catalysts from liquid and gas
phase processes revealed that the amount and nature of the species ads
orbed on the catalyst surfaces are different for these two types of pr
ocesses. In the case of a gas phase process, the amount of oligomers f
ormed on the catalyst surface was much higher. In the liquid-phase hyd
rogenation, these compounds showed a lower H/C ratio and were adsorbed
more strongly in comparison to those from the gas phase process.