Formation of acidic Brönsted (MoOx)−(Hy)+ evidenced by XRD and 2,6-lutidine FTIR spectroscopy for cumene cracking

Authors: S.N. Timmiati, A.A. Jalil, S. Triwahyono, H.D. Setiabudi, N.H.R. Annuar

Abstract:
2,6-Lutidine adsorbed IR spectroscopy has been employed to study the property of acidic sites on MoO₃ and Pt/MoO₃. 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 MoO3 and Mo–OH Brönsted acidic sites. All Brönsted acid sites were strong enough to retain outgassing at 473K, 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 (MoOx)⁻(Hy)⁺ on the hydrogen treated Pt/MoO₃, whereas the hydrogen adsorption on 2,6-lutidine pre-adsorbed catalysts showed the formation of protonic acid sites over Pt/MoO₃. These results strongly suggested that the interaction of molecular hydrogen with Pt/MoO₃ formed acidic Brönsted (MoOx)⁻(Hy)⁺ via a hydrogen spillover mechanism. In fact, no (MoOx)⁻(Hy)⁺ and protonic acid sites were observed on Pt-free MoO₃. The presence of (MoOx)⁻(Hy)⁺ enhanced the activity of Pt/MoO₃ 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.

Keyword:
MoO₃
Pt/MoO₃
2,6-Lutidine
(MoOx)⁻(Hy)⁺
Cumene hydrocracking

Published in: Applied catalysis A: General  (Volume 459, Pages 1-130, 24 May 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Formation of acidic Brönsted (MoOx)−(Hy)+ evidenced by XRD and 2,6-lutidine FTIR spectroscopy for cumene cracking

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