碳化钨预处理对烷烃反应活性的影响

EFFECT OF PRETREATMENT OF TUNGSTEN CARBIDE ON ALKANE REACTIONS

The effect of pretreatment of tungsten carbide on alkane reactions has been studied. No activity was observed on the tungsten carbide covered by amorphous carbon layers. On the tungsten carbide pretreated in H 2 at 1073 K for 5 h, the isomerization is dominant in dimethylbutane reactions while the cracking is in n hexane and 3 methylpentane reactions. Over the reduced sample passivated by 10%O 2/Ar at 633 K for 5 min, the isomerization becomes dominant in n hexane reaction, the cracking selectivity decreases from 68% to 5% while the selectivity for C 6 alkene increases from 14% to 30%. The reaction was also performed on the reduced sample exposed to air at room temperature for one year, the activity is ten times higher than that on the reduced sample. A significant increase in isomerization and cracking selectivity was observed, while the selectivity for C 6 alkene decreases to zero. The results indicate that if the tungsten oxide is formed on the tungsten carbide surface by adsorbed oxygen, the catalyst will be bifunctional, i.e. , alkane dehydrogenation and hydrogenation occur on the tungsten carbide and the isomerization occurs on the tungsten oxide; otherwise, the isomerization takes place on oxycarbide phase through a metallacyclobutane like intermediate, associated with the C 6 alkene formation in a significant amount.