Ž . Journal of Molecular Catalysis A: Chemical 154 2000 115–120 www.elsevier.comrlocatermolcata Influence of mild dealumination on physicochemical, acidic and catalytic properties of H-ZSM-5 S. Kumar 1 , A.K. Sinha ) , S.G. Hegde, S. Sivasanker Catalysis DiÕision, National Chemical Laboratory, Pune 411 008, India Received 28 June 1999; accepted 15 September 1999 Abstract Mild dealumination of ZSM-5 using HCl, acetylacetone and ammonium hexafluorosilicate resulted in a slight increase in the XRD crystallinity and overall surface area, but there was a marginal decrease in the micropore area and a considerable increase in mesopore area. 27 Al MAS–NMR spectra showed very weak signals due to octahedral aluminium for the samples treated with HCl and acetylacetone. FTIR spectra revealed small amounts of extra framework Al and four bands due to OH stretching vibration. The nature and intensity of the bands due to different hydroxyl groups varied depending on the treatment. Dealumination resulted in an increase in m-xylene conversion but a decrease in isomerization selectivity. The activity was maximum for HCl- and acetylacetone-treated samples that is attributed to the increase in the overall acidity Ž . both Lewis and Bronsted of samples as well as to the creation of mesoporosity. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Dealumination; ZSM-5; Acidity; Isomerization; Disproportionation; m-Xylene 1. Introduction The acidity of zeolites depends upon the wx framework SirAl ratio 1 . Thus, the acid cat- alytic properties of zeolites can be controlled by manipulating the SirAl ratio either during syn- thesis or by post-treatment dealumination meth- ods. Dealumination by steaming, SiCl treat- 4 ment, reaction with chelating agents like EDTA, acetylacetone, ammonium hexafluorosilicate, ) Corresponding author. Tel.: q 91-20-589-3761; fax: q 91-20- 589-3761. Ž . E-mail address: anilsinha65@yahoo.com A.K. Sinha . 1 Present address: A.P.S. University, Rewa, India. oxalic acid, etc. and leaching with HCl are some of the post-synthesis methods used to control wx the acidity of the zeolites 2 . To date, steaming is the most common dealumination technique used to prepare industrially important catalysts wx of high activity, selectivity and stability 3 . Mild steaming is found to greatly enhance wx the acidity of H-ZSM-5-type zeolites 4 . The enhancement in acidity is manifested in reac- tions like paraffin isomerization, paraffin crack- ing, and toluene disproportionation. Lago et al. wx 5 reported the generation of sites with en- hanced activity on mild steaming of H-ZSM-5 while severe steaming was found to reduce the activity. Infrared spectroscopy of ZSM-5 sam- ples after mild treatment with aqueous HF 1381-1169r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S1381-1169 99 00360-X