Journal of Catalysis 209, 413–416 (2002) doi:10.1006/jcat.2002.3628 An Approach to the Construction of Indexed Libraries for the Combinatorial Selection of Heterogeneous Catalysts Mar´ıa A. Aramend´ıa, Victoriano Borau, C´ esar Jim ´ enez, 1 Jos ´ e M. Marinas, Francisco J. Romero, 1 and Francisco J. Urbano Department of Organic Chemistry, University of C´ ordoba, Campus de Rabanales, Edificio C-3, Ctra. Nnal. IV, km 396, 14014 C´ ordoba, Spain Received December 4, 2001; revised March 26, 2002; accepted March 26, 2002 Two series of sublibraries consisting of data for an overall 10 mixtures (five supported metal catalysts each) were constructed and tested for the selection of catalysts in terms of activity and/or selectivity in the cracking/isomerization of n-heptane. c  2002 Elsevier Science (USA) Key Words: combinatorial chemistry; indexed library; heteroge- neous catalysis; metal-supported catalysts; zeolites; cracking; iso- merization; n-heptane. INTRODUCTION In the last few years, combinatorial methods have been extensively used to identify and optimize heterogeneous catalysts (1–5). However, most reported approaches rely on the use of parallel synthesis and high-throughput screen- ing techniques. Notwithstanding the impressive advances in this field, the efficiency of available methods for preparing and testing heterogeneous catalysts is rather low relative to homogeneous catalysts (6–8) and, especially, to active organic compounds, for which the libraries often contain thousands of compounds (9). Both the synthesis of hetero- geneous catalysts and their testing are subject to a number of shortcomings; also, most available methods for the syn- thesis and deconvolution of organic compounds are inap- plicable to them. An alternative methodology based on a genetic algorithm and an evolutionary approach has been successfully used to optimize the performance of heteroge- neous catalysts, however (10). Indexed (orthogonal) libraries are effective tools for de- riving information from mixtures of organic compounds (11, 12). Such libraries are constructed from two series of sublibraries. Thus, for the synthesis of dimeric com- pounds, each building block A n in the first sublibrary is reacted with a stoichiometric amount of an equimolar mix- ture of all other building blocks ( B 1 – B m ). In the second set, each reactant B m is treated with a stoichiometric amount of an equimolar mixture of all other components ( A 1 – A n ). 1 To whom correspondence may be addressed. Fax: +34 957 212 066. E-mail: qo2rosaf@uco.es. Using this methodology, researchers at Glaxo constructed a library from 40 acid chlorides and 40 amines or alco- hols. The process provided 80 mixtures of 40 components each, the screening of which exposed two novel leads against the neurokinin-3 receptor and the matrix metallo- proteinase collagenase (11). Other example consists of the preparation of a library composed from nine alcohols and six isocyanates to formally generate 54 carbamates, which were screened against acetylcholinesterase (12). These au- thors consider that the goal of this method is not so much synthetic as analytic and that its purpose is to gain informa- tion on as wide a universe of structures as possible in the shortest time and with the smallest cost. In this paper, we examine the potential of an indexed combinatorial library for selecting supported metal cata- lysts for the cracking/isomerization of n-heptane. The iso- merization of low-molecular-weight paraffins is of a high current interest on account of the fact that branched iso- mers exhibit high octane numbers and can be used as gaso- line additives to replace aromatic compounds, the usage of which should be reduced to avoid the environmental prob- lems they pose (13). In our case, the dimeric compound was replaced with a catalytic solid consisting of two materials, viz. a metal ( M ) and a support ( S). Five different metals (viz. Fe, Co, Ni, Pd, and Pt) were supported on as many zeolites (designated FER, ZSM-5, MOR, BEA, and USY) to obtain 10 mixtures with five components each where the identity of the metal or the support was fixed. This approach simplifies both the synthesis and the testing of catalysts; as a result, it enables catalytic activity measurements in conventional reactors and hence the identification of every reaction product. EXPERIMENTAL All zeolites (FER, ZSM-5, MOR, BEA, and USY) were purchased from Zeolyst Int. (refs. CP914, CBV8014, CBV90A, CP811E, and CBV760) in the following SiO 2 / Al 2 O 3 molar ratios: 55, 80, 90, 75, and 60, respectively. The metal precursors used were Fe(NO 3 ) 3 · 9H 2 O, Co (CH 3 COO) 2 · 4H 2 O, Ni(NO 3 ) 2 · 6H 2 O, Pd(NH 3 ) 4 (NO 3 ) 2 , 413 0021-9517/02 $35.00 c  2002 Elsevier Science (USA) All rights reserved.