Abstract:
Three methods for synthesis of aluminum-containing MCM-41 catalysts were investigated: synthesis under acidic condition, single-temperature synthesis under basic condition, and two-temperature synthesis under basic condition. AI-MCM-41 was directly synthesized by hydrothermal crystallization from a mixture of starting substance including aluminum compounds. To define an appropriate synthesis method, several parameters were varied such as acidity of the gel, type of templates (cetyltrimethylammonium chloride and bromide), type of silicon source (tetraethyl orthosilicate and water glass), type of aluminum source (sodium aluminate and aluminum isopropoxide), and silicon to aluminum ratios in gel (20:80). The synthesized products were characterized using X-ray diffraction, X-ray fluorescence, inductively coupled plasma-atomic emission, solid state 27Al-nuclear magnetic resonance, nitrogen assorption, and ammonia-temperature programmed desorption techniques. White solids with the highly ordered structure of MCM-41 were obtained from the gel in basic condition at the temperature of 100℃ for 2 days and subsequently at 125℃ for 6 days. Effect of temperatures (350 to 550℃) on catalytic activity of AI-MCM-41 in polypropylene degradation under nitrogen was studied using a ratio of catalyst to polypropylene of 40:100. At the temperature of 550℃, gas products are mainly obtained from polypropylenedegradation with 100% conversions of polypropylene. Formation of iso-butane is favored at the temperature of 350℃ while further conversion of iso-butane to propylene takes place effectively at higher temperatures. Methane is formed in a small amount but increases at higher temperatures. Highly dispersion of Bronsted acid sites on the large catalyst surface is accounted for the high catalytic activity of AI-MCM-41. Values of percent conversion and product selectivity are slightly changed with increasing Si/AI ratio in catalyst. Formation of coke deposited in catalyst is significantly decreased with increasing Si/AI ratio in catalyst.