Magnetochemical Studies on Adsorption on the Fine-Powdered Nickel Catalystt

The poisoning of Ni/SiO2 catalysts by H2S and ethylene oxide adsorption and the subsequent chemisorption of H2 at 15°C were described by the method of low field magnetization measurements. When H2S was introduced on the catalyst, it was estimated by the slope of magnetizationvolume isotherms that one molecule of H2S dissociatively covered four or five Ni atoms. The bonding number of H2S with Ni atoms was calculated from the dispersion value of Ni crystallites assuming that the adsorption occured on the top of Ni atoms. It is in good agreement with the result obtained from the assumption of selective attack by H2S on finer particles of the Ni crystallites on which H2 adsorption proceeded in the range of small coverage and was shown at the 1st stage in the magnetization-volume isotherm. The result concerning the ethylene oxide adsorption on Ni was similar to those observed for ethylene.The mechanism of ethylene oxide poisoning would be mainly geometrical blocking in a manner equal to the active or inactive sites, whereas H2S selectively attacked the active sites, finer parts of Ni crystallites, and then transformed these to inactive surface compounds. The magnetization changes due to the H2 adsorption on Ni-Cu/SiO2 were estimated and the influence of Cu addition to the superparamagneitc Ni/SiO2 composition appeared in the sharp decrease in magnetization changes caused by the initial H2 adsorption on the bimetallic particles. It seems that the surface composition of the alloy system was different from the bulk one and the surface enrichment in Cu was expected. The magnetization-volume isotherms for th e adsorption of H2 and CO were observed at -75and -184°C. H2 chemisorption was observed as much as 9 ml(NTP)/g-Ni at -184°C and CO adsorption occured at the bonding with Ni atoms in the bridged model and transfered to the single bonding at higher coverage at -75°C.