The Malaysian Journal of Analytical Sciences, Vol 11, No 1 (2007): 117-123 117 BIFUNCTIONAL Nb/Ti-MCM-41 CATALYST IN OXIDATIVE ACIDIC REACTION OF CYCLOHEXENE TO DIOL Zainab Ramli*, Mazidah Abdul Shukor and Didik Prasetyoko Dept. of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor D.T. Keywords : bifunctional catalyst, Nb/TiMCM -41, oxidative-acidic, diol Abstract Bifunctional oxidative and acidic catalyst was prepared by incorporating titanium ion (Ti 4+ ) and niobic acid in mesoporous molecular sieves MCM -41 structure. The catalyst is active both in oxidation, and acid-catalyzed reaction of olefin to diol. Nb/Ti-MCM -41 catalyst was prepared by first synthesizing Ti-MCM -41 by hydrothermal method, followed by subsequent impregnation of niobic acid (Nb) into Ti-MCM -41 at various %wt Nb loading. The framework structure of Ti-MCM -41 collapsed after incorporation of Nb but the tetrahedral form of Ti 4+ still maintained with octahedral Nb species. Both Brønsted and Lewis acid sites are present in all Nb/Ti-MCM-41 samples. The formation of cyclohexanediol in the epoxidation of cyclohexene proved the bifunctional oxidative and acidic catalyst through the formation of cyclohexane oxide. The yield increased with the increase amount of the Brønsted acid sites provided by niobium species . Abstrak Mangkin dwifungsi oksidatif berasid disediakan dengan memasukkan ion titanium (Ti 4+ ) dan asid niobik dalam struktur penapis molekul mesoliang MCM -41. Mangkin aktif dalam kedua-dua tindak balas bermangkinkan pengoksidaan dan asid bagi olefin kepada diol. Mangkin Nb/Ti-MCM -41 disediakan bermula dengan mensintesis Ti-MCM -41 secara hidroterma, diikuti dengan pengisitepuan asid niobik (Nb) ke dalam Ti-MCM-41 pada berbagai % berat muatan Nb. Struktur bingkaian Ti-MCM-41 didapati runtuh selepas kemasukan Nb tetapi struktur tetrahedron Ti 4+ masih kekal dengan spesies octahedron Nb. Kedua-dua tapak asid Brønsted dan Lewis hadir dalam semua sampel Nb/Ti-MVM -41. Pembentukan sikloheksandiol dalam pengepoksidaan sikloheksena membuktikan mangkin adalah dwifungsi oksidatif berasid melalui pembentukan sikloheksan oksida. Hasil bertambah dengan pertambahan tapak asid Brønsted yang disediakan oleh spesies niobium. Introduction Mesoporous molecular sieves (MMS) have attracted a great deal of world-wide attention among researches in the fields of inorganic synthesis, functional materials, and heterogeneous catalysis, due to their regular pore structure, uniform pore diameter and high surface area[1,2]. One of the interesting fields in development of catalyst is the creation of two active sites in a single material catalyst, called bifunctional catalyst. The bifunctional catalyst in this study is active both in oxidation and acid-catalyzed reactions. Didik et al . [3-6] has reported the activity of bifunctional catalysts prepared by incorporation of sulphate, zirconia, niobium on TS-1 molecular sieve, on the epoxidation of 1-octene to its respective diol. The niobium incorporated TS-1, Nb/TS-1 catalyst [6] was found to be the most active catalyst in which the diol yield depends on the amount of incorporated niobium. However the same catalyst when applied in epoxidation of cyclohexene did not yield any desired product. The reason might be due to the microporosity of TS-1 being medium pore class molecular sieve having pore size of ~ 5Å. To prove that the activity of Nb/TS-1 as the bifunctional oxidative-acidic catalyst was hindered by pore restriction, we chose MCM-41 with the pore size in mesoporous range as the support for niobium species. In this study, Ti-MCM-41 (TM) and Nb/Ti-MCM-41 (Nb/TM) samples were prepared and characterized using XRD, FTIR and UV-Vis DR. Acidity was measured by FTIR using pyridine as probe molecule. The catalysts prepared are tested in the epoxidation reaction of cyclohexene. Experimental Synthesis of Ti-MCM-41 and Nb/Ti-MCM-41 Ti-MCM-41 (TM) was prepared by direct hydrothermal following method described by Blasco et al.[7] Tetraethylorthosilicate,(TEOS) was placed into a teflon beaker and stirred. Tetraethylorthotitanate(TEOT) in isopropyl alcohol was added dropwise into the TEOS. The temperature of the mixture was raised to 35 o C and mixed homogeneously for half an hour followed by cooling to 0 o C (solution A). The tetramethyammonium