Adsorption and reaction of cyclopropane and hydrogen on nickel: Changes in selectivity with temperature

Abstract

A comparative study was made of the cyclopropane chemisorption on pure nickel film surfaces and of the hydrogenation and hydrocracking of cyclopropane on both the films and a reduced nickel catalyst. In a range of higher coverages, the chemisorption of cyclopropane at 273 °K was accompanied by selfhydrogenation to propane, and, as a characteristic feature of the process on nickel, cracking to methane and ethane was also observed. Some further data concerning composition and properties of the chemisorbed layers are also given. Cyclopropane was reacted with hydrogen on nickel films in an UHV apparatus at 195 and 273 °K, and in the range of 300–600 °K using a microcatalytic-pulsed reactor coupled to a gas chromatograph. For the purpose of comparison, hydrocracking of propane was also investigated under the same conditions on the nickel powder catalyst. From the temperature variation of the product composition thus obtained, two types of cyclopropane cracking could be distinguished. With the low-temperature selective hydrocracking, the percentage of methane and ethane in overall product was constant over the range of 195–500 °K. Beyond this range the nonspecific hydrocracking began, characterized by the increasing proportion of cracking in products and by the prevalence of methane over ethane. No distinction could be made between the latter process and the propane or propylene hydrocracking. Some mechanistic consequences of the experimental findings are discussed. A concerted simultaneous splitting of two bonds in the chemisorbed cyclopropane ring is suggested as the reaction path for the low-temperature fragmentation.