Hydrogen effect on α-Al 2O 3 supported Ni catalyst for steam methane reforming reaction

Abstract

Nickel particles in a catalyst for steam methane reforming showed more sintering at lower temperature than at higher temperature with H 2 addition. A Ni(6.8 wt.-%)/α-Al 2O 3 catalyst showed a continuous and irreversible deactivation over 430 h due to sintering of Ni in the presence of 2% H 2 addition at 862 K. At 1017 K, the catalyst also showed an activity decrease with 2% H 2 addition, but the activity was stabilized at a certain level over 130 h and it recovered after the H 2 addition was stopped. The nickel sintering corresponded to the activity change in the experiment at 1017 K as well as that at 862 K. The catalyst in the form of 5 mm sphere was short-packed in 10 mm length, and the standard conditions were 9.7 bar, a steam/carbon(S/C) = 3, and W/F= 26s. The sintering was confirmed by SEM observation. Sintering reference experiments in H 2/N 2 and in H 2O + H 2/N 2 under conditions equivalent to those of the above activity measurements showed that carbon-bearing components played an important role in preventing the sintering. Sintering did not occur in H 2/N 2 atmosphere and much more sintering occurred in H 2O + H 2/N 2 atmosphere than under the activity measurement conditions. In a long-packing experiment conducted in analogy to an actual plant operation with an axial temperature gradient of 883–980 K, the same phenomena as those in the short-packing experiment were confirmed by SEM observation. However, the deactivation did not appear because in the tube the fraction of the deactivation section where the temperature is low and P H2 is high is small. This seems to be the reason why no deactivation by H 2 has ever been reported in actual plant operations.