Author's personal copy Applied Catalysis A: General 459 (2013) 8–16 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General j ourna l h omepa ge: www.elsevier.com/locate/apcata Formation of acidic Brönsted (MoO x ) - (H y ) + evidenced by XRD and 2,6-lutidine FTIR spectroscopy for cumene cracking S.N. Timmiati a , A.A. Jalil a , S. Triwahyono b,c,∗ , H.D. Setiabudi a , N.H.R. Annuar b a Institute of Hydrogen Economy, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia b Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia c Ibnu Sina Institute for Fundamental Science Studies, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia a r t i c l e i n f o Article history: Received 20 February 2013 Received in revised form 28 March 2013 Accepted 30 March 2013 Available online 15 April 2013 Keyword: MoO3 Pt/MoO3 2,6-Lutidine (MoOx) - (Hy) + Cumene hydrocracking a b s t r a c t 2,6-Lutidine adsorbed IR spectroscopy has been employed to study the property of acidic sites on MoO 3 and Pt/MoO 3 . The results showed that both catalysts possess doublet adsorption bands at 1605 + 1585 cm -1 , ascribed to Lewis acid sites, and duo-doublet bands at 1660 + 1650 and 1640 + 1630 cm -1 , ascribed to hydroxyl groups; these indicate an OH defect structure of MoO 3 and Mo–OH Brönsted acidic sites. All Brönsted acid sites were strong enough to retain outgassing at 473 K, while a considerable number of relatively weak and medium acid sites as well as strong Lewis acid sites existed. The addition of Pt slightly altered the ratio of Lewis/Brönsted acid sites and distribution of Lewis acid sites. The XRD result confirmed the formation of molybdenum oxyhydride (MoO x ) - (H y ) + on the hydrogen treated Pt/MoO 3 , whereas the hydrogen adsorption on 2,6-lutidine pre-adsorbed cata- lysts showed the formation of protonic acid sites over Pt/MoO 3 . These results strongly suggested that the interaction of molecular hydrogen with Pt/MoO 3 formed acidic Brönsted (MoO x ) - (H y ) + via a hydrogen spillover mechanism. In fact, no (MoO x ) - (H y ) + and protonic acid sites were observed on Pt-free MoO 3 . The presence of (MoO x ) - (H y ) + enhanced the activity of Pt/MoO 3 in the cumene hydrocracking in which the rate conversion of cumene increased by about 30%, while the apparent activation energy decreased by approximately 28 kJ/mol. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Recently, solid acid catalysts based on Al 2 O 3 , zeolite, ZrO 2 , and MoO 3 have been explored widely due to stability and regenerative properties and the fact that they are highly active at a wide range of reaction temperatures [1–3]. Bifunctional catalysts consisting of acidic oxides and noble metals showed high efficiency in the acid catalytic reaction, such as alkylation, isomerization and cracking. An acid catalytic reaction is normally carried out in the presence of hydrogen due to the role of hydrogen in the formation of protonic acid sites and the removal of coke deposits from the surface cata- lysts [4–6]. For certain classes of catalyst, the presence of a noble metal is indispensable in the interaction with molecular hydrogen, which leads to the formation of protonic acid sites [7,8]. Recently, several research groups have extensively focused on the study of MoO 3 type catalysts for acid catalytic reactions. Blekkam et al. reported that the treatment of MoO 3 with H 2 /alkane ∗ Corresponding author at: Ibnu Sina Institute for Fundamental Science Studies, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. Tel.: +60 7 5536076; fax: +60 7 5536080. E-mail addresses: sugeng@utm.my, sugengtw@gmail.com (S. Triwahyono). mixture yielded an active and selective catalyst for hexane isom- erization [9,10]. They concluded, based on the XRD, XPS and HRTEM results, that a molybdenum compound containing car- bon as an oxycarbide (MoO x C y ) acts as an active phase for alkane isomerization. In addition, Ledoux and co-workers showed that oxygen-modified Mo 2 C and carbon-modified MoO 3 were active and selective for heptane isomerization [10,11]. Molybdenum oxy- carbide, which is formed by incorporating carbon atoms in the molybdenum oxide lattice, has been considered to be the active phase for heptane isomerization. Katrib et al. suggested that the MoO 2 phase was responsible for hexane isomerization in which the isomerization of MoO 2 proceeds via a bifunctional mechanism [12]. In contrast, Wehrer et al. pointed out that MoO has been proposed to act as the active phase for alkane isomerization after incom- plete reduction with pure H 2 [13–15], and the catalytic activity of partially-reduced MoO 3 was strongly dependent on the reduction temperature [16]. In addition to the molybdenum oxide species, Matsuda et al. reported that H 2 -reduced MoO 3 was accompanied by an increase in the surface area and became an active and selec- tive catalyst for heptane isomerization [3]. The surface area can be markedly enlarged when MoO 3 is reduced through the forma- tion of a hydrogen molybdenum bronze H x MoO 3 phase. Recently, they also studied the effects of H 2 reduction on MoO 3 , Pt/MoO 3 0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2013.03.046