Applied Catalysis A: General 228 (2002) 127–133 Structure and reactivity of sol–gel sulphonic acid silicas Karen Wilson ∗ , Adam F. Lee 1 , Duncan J. Macquarrie, James H. Clark Department of Chemistry, Green Chemistry Group, University of York, Heslington, York YO10 5DD, UK Received 24 September 2001; received in revised form 8 November 2001; accepted 8 November 2001 Abstract A range of mesoporous solid sulphonic acid catalysts have been prepared from a mercaptopropyl-trimethoxysilane (MPTS) precursor by sol–gel synthesis. The creation of surface sulphonic acid functionality via thiol oxidation has been followed by XPS and Raman spectroscopy. It is possible to continuously vary the sulphonic acid loading from 1 to 12wt.% while maintaining pore volume and mesostructure. The resulting materials exhibit high thermal stability and acid strength across the composition range and show good activity and selectivity in esterification and condensation reactions. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Solid acid catalysts; Organically modified silica; Clean technology; Green chemistry; Sulphonic acid; Mesoporous silica 1. Introduction The syntheses of many fine and speciality chemicals often relies on homogeneous mineral acids, bases or metal salts, which are frequently used in stoichiomet- ric amounts. Tightening legislation on the treatment and disposal of excessive toxic waste, produced dur- ing the separation and neutralisation of products from these reaction media, is driving industry to consider cleaner technologies, including the use of heteroge- neous catalysis. While zeolites are widely used as solid acid catalysts in gas phase chemistry, their use in liquid phase organic synthesis is limited by their small pore sizes (<8 Å) which make them unsuitable for reactions involving bulky substrates. However, recent develop- ments in materials chemistry have led to the discovery of the M41S family of mesoporous molecular sieves ∗ Corresponding author. Fax: +44-1904-434546. E-mail address: kw13@york.ac.uk (K. Wilson). 1 Present address: Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, UK. [1] offering pore sizes in the range 20–100 Å and, thus, new avenues for liquid phase solid acid catalysis. The subsequent report of neutral templating meth- ods using long chain alkylamines to prepare hexag- onal mesoporous silicas (HMS) [2] has attracted much interest since the template removal process by solvent extraction is simple and environmentally benign. In addition, the use of a neutral templat- ing process also opens possibilities for incorporating organo-functionalised silanes into the silica frame- work during the sol–gel process [3,4]. These direct preparation routes offer the opportunity to incorporate higher loadings of organic groups than those attain- able via post-grafting techniques [4]. Through this ap- proach a range of materials containing phenyl, cyano vinyl, amine, thiol, carboxylic acid, or sulphonic acid groups can be prepared [5,6]. Derivatisation of selected materials can also subsequently be used to prepare immobilised organo-metallic complexes [7]. Organically modified silicas are widely used in separation science [8], and the techniques for their preparation are well documented. For example silica 0926-860X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0926-860X(01)00956-5