Oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides

The oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides is reported. High yields of olefins and only moderate formation of carbon oxides was observed. Both are primary products that hardly interconvert under the reaction conditions used. Addition of chloride increases the rate of reaction, while slightly decreasing the selectivity to olefins. The addition of carbon dioxide strongly decreases the rate of reaction, the negative order of 0.5 indicating that two active Li+ sites are blocked by the adsorption of one CO2 molecule. The reaction proceeds at low oxygen pressure primarily via elimination of dihydrogen, while at higher oxygen partial pressure the hydrogen elimination occurs via water formation. It is speculated that dehydrogenation and cracking involve Li+ and a rather nucleophilic oxygen site.