© Kimia ITS – HKI Jatim 11 Akta Kimindo Vol. 1 No. 1 Oktober 2005: 11 –16 AKTA KIMIA IND O NESIA Niobic Acid Dispersed on the Surface of TS-1: Acidity Study* Didik Prasetyoko a ,**, Zainab Ramli a , Salasiah Endud a and Hadi Nur b a Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. b Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. ABSTRACT Bifunctional oxidative and acidic catalyst was prepared by incorporation of titanium ion (Ti 4+ ) and niobic acid in zeolite molecular-sieve. Nb/TS-1 was prepared by hydrothermal synthesis of Titanium silicalite, TS-1, calcination in air and subsequent impregnation of niobium (3-20 wt% Nb2O5) into TS-1. Acidity of the sample was characterized by pyridine adsorption technique. Pyridine adsorption study shows both Brønsted and Lewis acid sites are present in all Nb/TS-1 samples. ABSTRAK Katalis oksidatif bifungsional dan asam telah dipersiapkan melalui penggabungan ion titanium (Ti4+) dan asam niobat di dalam penyaring-molekuler zeolit. Nb/TS-1 dipersiapkan secara sintesis hidrotermal titanium silikat, TS-1, kalsinasi di udara dan penjenuhan niobium (3-20 % berat Nb2O5) ke dalam TS-1. Keasaman contoh dikarakterisasi dengan teknik adsorpsi piridin. Pengkajian adsorpsi piridin memperlihatkan bahwa kedua asam Brønsted dan asam Lewis terdapat di seluruh contoh Nb/TS-1. INTRODUCTION Development of efficient catalysts is a challenge in catalysis research. One of the interesting fields is the creation of two active sites in a single material catalyst, so called bifunctional catalysts. The catalysts are potentially active for consecutive processes. Bifunctional oxidative and acid catalysts have been prepared by incorporation of trivalent metal ions (Al 3+ , B 3+ , Fe 3+ , Ga 3+ ) and titanium ion (Ti 4+ ) together in the framework of zeolites (Trong On et al., 2003). The catalysts being active both in the oxidation and acid catalyzed reactions. In a previous study, van der Wall (1998) has demonstrated that bifunctional Ti-Al-beta zeolites can lead to acid-catalyzed consecutive reactions. The catalysts were active in epoxidation of alkenes to produce epoxide and diol. However, it is difficult to control the number of oxidative site together with acidic sites due to some competition between titanium and aluminium to become isomorphously substitute in the framework of zeolites. In order to overcome such problem, a new catalyst system has been design. Our work focuses on the enhancement of the catalytic performance of bifunctional oxidative and acidic catalysts by incorporation of titanium and niobium into zeolite molecular-sieve (Prasetyoko et al., 2005). Titanium silicalite (TS- 1) molecular-sieves have attracted much attention during the last decade because of their interesting catalytic properties in oxidation reactions (Tarramasso et al., 1983). Niobium has been loaded on the surface of TS-1 to introduce acidity. Hydrated niobium pentoxide (niobic acid, Nb2O5. nH2O), one of the niobium compounds shows high catalytic activity, selectivity, and stability for acid-catalyzed reactions (Iizuka et al., 1986; Okazaki et al., 1987). It has Brønsted and Lewis acid sites with high acid strength (Ho ≥ - 5.6), in which the acid strength corresponds to 70% H2SO4. Niobic acid is an unusual solid acid, showing high acid strength in spite of its water content, while other kinds of acidic metal oxides show decreasing of the acidic property by absorbing water, while niobic acid (Okuhara, 2002, Tanabe, 2003). A supported metal oxide often shows a different catalytic activity from its bulk oxide. It depends on the support materials and niobium precursors. It has been reported that for supported niobium oxide on silica, both Brønsted * Makalah ini disajikan pada Seminar Nasional Kimia VII, di Surabaya 9 Agustus 2005 ** Corresponding author Phone: +607-5534530; Fax: +607-5536162; e-mail: didik.prasetyoko@gmail.com