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Light olefins such as ethylene, propylene and butenes are essential raw chemicals in the petrochemical industry, and demand for these light olefins continues to increase year by year. Most light olefins are produced by steam cracking of naphtha, but the output composition is uncontrollable and propylene and butenes are present as by-products. In addition, steam cracking of naphtha occurs at high temperature so consumes a large amount of energy. Therefore, processes to obtain controlled production of light olefins under mild reaction conditions are very desirable. Zeolites are crystalline aluminosilicates with threedimensionally connected framework structures and have important properties such as strong acidity, high surface area, and regular pores with sizes close to the molecular size of hydrocarbons. In addition, zeolites are stable under high temperature conditions, so are widely used in industrial processes. Production of light olefins from various sources such as naphtha1)~10), methanol11)~16), ethanol17) and acetone18)~20) over zeolite catalysts has been investigated extensively, and the reaction mechanisms over zeolite have also been evaluated21)~30). Light olefins are intermediate products of the reaction, so suppression of consecutive reactions forming aromatics and coke from light olefins is required for selective production. Furthermore, the pore size of zeolites is close to the molecular size of light olefins and aromatics, so the reaction rates on acid sites and diffusion velocities of molecules inside the pores, which are related to the residence time of molecules inside the pores, strongly affect the progress of such undesirable reactions. P r ev ious ly, s i l y l a t ed18),19) o r a l ka l i -me ta l i on exchanged20) zeolites were prepared intended to weaken the acid sites, which succeeded in producing isobutylene selectively from acetone. Isomorphous substitution of Al by other trivalent elements (e.g., B, Ga, Fe and Zr) in the zeolite framework31),32), such as LTA, MFI, MTW and MOR, to form metallosilicates can modify the acidity of zeolites. For example, the methanol to olefins reaction over ferrisilicate with MFI-type zeolite structure showed low selectivity for aromatics33),34). In the catalytic reaction over zeolite, the feedstock must diffuse inside the zeolite pores from the bulk fluid because the active sites are located on the surfaces of the zeolite pores. The product molecules formed on 277 Journal of the Japan Petroleum Institute, 60, (6), 277-287 (2017)

Synthesis of Light Olefins from Oxygenated Organic Compounds over Metallosilicates with MFI and MTW-type Zeolite Structures