Activation and Aromatization of Propane on Solid Acid Catalysts

Activation and Aromatization of Propane on Solid Acid Catalysts 

Using labeled - C-2-propane as reactant and gallium-modified silicalite-1 (wsi/ = 480, 0.96 wt.% Ga) and zeolites Ga/HZSM-5 (zrsi/ Ai = 35, 1.02 wt.% Ga) and HZSM-5 ( si/z7Ai = 35) as catalysts, Derouane el al. 105,178-181 and Ivanova 

In contrast, an extremely low activity was observed for the gallium-modified silicalite-1. scrambling started first at 723 K, which clearly indicates that Bronsted acid sites are necessary to activate propane adsorbed on zeolites Ga/ HZSM-5 179,181. A low activity was also observed for C-2-propane adsorbed on zeolite HZSM-5 in the absence of gallium. On this catalyst, C scrambling was observed after heating at 573 K for 20 min, and the theoretical 2 1 ratio of the signal intensities of methyl and methylene groups was reached after 80 min at 573 K. 

The finding of the low-temperature activation of propane on zeolite Ga/HZSM-5 indicates a bifunctional reaction mechanism 179,181. The highly dispersed gallium oxide species in close vicinity to the Bronsted acid sites promote the initial activation of propane. Derouane et al. 179,181 further showed that hydrogen inhibits the activation of propane. This effect was explained by a competitive adsorption of hydrogen on the gallium species or even by a reduction of Ga to Ga species. 

Internal hydrogen scrambling and isotope redistribution between propane and solid catalysts may proceed by a rather complex mechanism involving several pathways with different rates and activation energies. The competitive pathways cannot be distinguished if the temperature for activating propane on zeolites is 

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