The Behavior Of Carbon Deposition In The Ethane Dehydrogenation Reaction And The Modification Of Surface Acid Properties Of The Catalyst

The stability of Ga2O3/HZSM-5 for dehydrogenation of ethane to ethylene in the presence of CO2 is investigated. The relationship among the acidity, activity (for dehydrogenation and cracking) and coking on the catalyst has been investigated and discussed in order to find the roads to inhibit and eliminate the coke to enhance the stability of the catalyst.Firstly, coking and decoking phenomena on Ga2O3/HZSM-5 are investigated by Laser Raman, TG-MS and NH3-TPD et al. The results demonstrate that coking and cracking of ethane can occur easily on the strong acidic sites. The formed graphitic coke is difficult to be removed in the reaction process, which is the main reason for deactivation of the catalyst. Steam containing air atmosphere can improve the efficiency of decoking, especially for the graphitic coke. The catalytic activity is restored effectively under H2O-air flow at 420℃.Modification of alkali and alkali earth metals on Ga2O3/HZSM-5(22) can reduce the amount or the strength of the strong acidic sites of the catalyst, which enhances the stability of the catalyst due to inhibiting the coking rate. Cracking of ethane is also inhibited over the modified catalyst, and consequently the selectivity of ethylene is improved. However, dehydrogenation of ethane to ethylene can be inhibited as well if the amount of the strong acidic sites of the catalyst is reduced too much.Ga2O3/HZSM-5(200) modificated by element of B can increase the amount of the weak acidic sites of the catalyst, which has no effect upon the deactivation of the catalyst without further graphitic coking if the amount of B is in excess of 0.25. However, Cracking of ethane is enhanced over Ga2O3/H-BZSM-5(200), which leads to decreasing of the selectivity of ethylene. Ga2O3/HZSM-5(200) modificated by element of B can reduce the amount of the strong acidic sites of the catalyst, which inhibits the activity of cracking of ethane, and consequently the selectivity of ethylene is improved if the amount of B is equal to 0.25.