Comparison of mesoporous solid acid catalysts in the production of DABCO by cyclization of ethanolamine I. Synthesis and characterization of mesoporous solid acid catalysts Manickam Selvaraj * , Byoung Ryul Min, Yong Gun Shul, Tai Gyu Lee * Department of Chemical Engineering, Yonsei University, 134, Shinchon-Dong, Seodaemun-gu, Seoul 120-749, Korea Received 23 February 2004; received in revised form 14 May 2004; accepted 2 June 2004 Available online 14 August 2004 Abstract Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn–Al-MCM-41) with Si/(Zn + Al) ratio equal to 75, 151, 228, 304 and 380 and only aluminum ions (Al-MCM-41) with Si/Al ratio equal to 21, 42, 62, 83 and 104 respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA + ) surfactants as template in the absence of aux- iliary organics. The mesoporous materials viz. Zn–Al-MCM-41 and Al-MCM-41 were characterized using several techniques. e.g. ICP-AES, XRD, FTIR, TG/DTA, Nitrogen adsorption, 27 Al-MAS-NMR, SEM, TEM, XPS and pyridine acidity (TPD and FTIR) measurements. The d-spacing value and unitcell parameter in the Zn–Al-MCM-41 and Al-MCM-41 decreases by increasing the metal ions content. FT-IR studies showed that zinc ion was incorporated into the hexagonal mesoporous Al-MCM-41 materials, however, the wavenumber of the anti-symmetric Si–O–Si vibration bands (1096 cm 1 ) in Zn–Al-MCM-41 are higher than those in Al-MCM-41 (1083 cm 1 ). These bands should be due to the increase of the mean Si–O distance in the wall caused by the sub- stitution of the small ionic radii of silicon by the larger ionic radii of zinc. The surface area, pore diameter, pore volume of Zn–Al- MCM-41 is smaller than that of Al-MCM-41 while the hydrothermal stability and acid sites in the Zn–Al-MCM-41 are higher than that of Al-MCM-41 due to increasing protons with the aluminum ions non-framework by the introduction of zinc ions. Thus Bron- sted and Lewis acid sites in Zn–Al-MCM-41 are same, but its acid sites are higher than Al-MCM-41. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Zn–Al-MCM-41; Al-MCM-41; Hydrothermal stability; Bronsted acidity; Lewis acidity 1. Introduction Solid acid catalysts have served as important func- tional materials for the petroleum refinery industry, such as in the cracking processes, and for the production of chemicals [1]. At present, about 180 industrial processes using solid acids are in operation, featuring acids such as zeolites, oxides, mixed oxides including heteropoly acids, and phosphates [2]. In contrast, a significant num- ber of acid-catalyzed reactions, such as Friedel–Crafts reactions, esterification, hydration, and hydrolysis, are still carried out using conventional acids, such as H 2 SO 4 and AlCl 3 . However, processes involving con- ventional acids are typically associated with problems of high toxicity, corrosion, catalyst waste, use of large amounts of catalyst, and difficulty of separation and recovery. Because solid acids are environmentally friendly with respect to corrosiveness, safety, less waste, and ease of separation and recovery, replacement of these liquid acids with solid acids is desirable in the chemical industry. 1387-1811/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.06.014 * Corresponding authors. Tel.: +82 2 2123 5751; fax: +82 2 312 6401. E-mail addresses: selvarajman25@yahoo.com (M. Selvaraj), teddy. lee@yonsei.ac.kr (T.G. Lee). www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 74 (2004) 143–155