Reactions between Hydrocarbons and Deuterium on Chromium Oxide Gel. I. General¹

Mechanistic Insight in the Ethane Dehydrogenation Reaction over Cr/Al2O3 Catalysts

“…This experimental finding confirms the results reported by Burwell et al for higher alkanes on Cr 2 O 3 [12] and the recent theoretical work of Lillehaug et al [13]. (2) We found no evidence that coke deposits formed during the initial activation of the catalyst material are involved in the ethane dehydrogenation cycle since no isotopic scrambling of ethylene was observed.…”

“…This observation is in line with results reported by Burwell et al for higher alkanes on Cr 2 O 3 [12] and the recent theoretical work of Lillehaug et al [13]. The absence of bi-deuterated ethane, as would be expected for ethene hydrogenation in the presence of D 2 [12], further indicates that there is little back formation of ethane from ethene under the applied reaction conditions. Ethene experiences more H-D exchange than ethane, and significantly more mono-than bi-deuterated ethene molecules are observed.…”

“…For this purpose, we have conducted isotopic labelling experiments for an ethane dehydrogenating Cr/Al 2 O 3 catalyst making use of labelled 13 C-ethane and deuterium. Secondly, the data obtained allow us to extend the work of Burwell [11,12] to alumina-supported chromium oxide catalysts and discuss the obtained insights in relation with the recently published theoretical study by Lillehaug et al on the same reaction system [13].…”

“…The mass fragments of ethane (figure 5a) and ethene (figure 5b) are both shifted one mass unit higher after introduction of 1) 13 C ethane compared to 12 C ethane. No change in the fragmentation pattern is observed with time (30-180 s after on-set of the 1) 13 …”

“…The group of Burwell did seminal work in the 1960s on Cr 2 O 3 by using D-labelled hydrocarbons and deuterium D 2 [11,12]. Unfortunately, to our best knowledge, there are no similar studies for supported chromium oxide catalysts.…”