Journal of Catalysis 183, 155–158 (1999) Article ID jcat.1998.2379, available online at http://www.idealibrary.com on RESEARCH NOTE Simultaneous Quantification of Brønsted- and Lewis-Acid Sites in a USY Zeolite Kevin J. Sutovich, ∗,† Alan W. Peters, † Edward F. Rakiewicz, †,1 Richard F. Wormsbecher, † Susan M. Mattingly, ∗ and Karl T. Mueller ∗,2 ∗ Department of Chemistry, The Pennsylvania State University, 152 Davey L aboratory, University Park, Pennsylvania 16802; and † Washington Research Center, W. R. Grace and Company, 7500 Grace Drive, Columbia, Maryland 21044 Received September 18, 1998; revised December 7, 1998; accepted December 7, 1998 In this report, experimental methods and calculation procedures are described for direct and simultaneous quantification of the Brønsted- and Lewis-acid site concentrations in a sample of USY zeolite. The concentrations of both types of acid sites are character- ized by solid-state 31 P MAS NMR spectroscopy of trimethylphos- phine oxide probe molecules. The errors associated with the area measurements in the NMR spectrum, and hence the errors in the concentration measurements reported, are estimated with Monte Carlo simulations applied with spectral line-fitting and deconvolu- tion procedures. c  1999 Academic Press Key Words: solid-state NMR; acid-site quantification; trimethyl- phosphine oxide; Brønsted acidity; Lewis acidity; USY zeolite. A number of experimental methods are readily avail- able for the characterization and quantification of acid sitesinsolids.Theseincludethermalmethods,temperature- programmed desorption (TPD), and microcalorimitry which are all either selective for Brønsted sites (1) or do not distinguish clearly between Lewis- and Brønsted-acid sites. Infrared techniques,dependingon the probe used,can have the same difficulty.Even ifa band isidentifiable asdue to an interaction with a Lewis site, relative quantification is often difficult. Therefore the simultaneous quantification of both types of sites in a solid acid is an important goal, with the ultimate desire being an understanding of the relationship of atomic-level structure to catalytic activity and selectivity. Studies utilizing solid-state NMR spectroscopy of probe molecules containing NMR-active 31 P nuclei have demon- strated the use of the wide 31 P chemical shift dispersion for the identification of Lewis and Brønsted sites (2–6). Since the quantification of spectra from spin-1/2 nuclei is rela- 1 Current address: PPG Industries, Inc., 4325 Rosanna Drive, Allison Park, PA 15101. 2 To whom correspondence should be addressed. E-mail: ktm2@psu. edu. tively straightforward, these results are in principle quanti- tative measures of acid site concentrations. The use of 31 P as a reporting nucleus for solid acidity has been demon- strated using a number of 31 P-containing compounds, with most promising results reported using trimethylphosphine (TMP) as the probe. However, TMP is a dangerous liquid at room temperature, and there are difficulties in handling TMP and in preparing solid acid standards for the quanti- tation step. Studies of the more stable trimethylphosphine oxide (TMPO) have been reported on amorphoussilica–alumina surfaces(3,7),and recentlywe reported the successfulcom- pletion of 31 P magic-angle spinning (MAS) NMR studies of TMPO complexed with acid sites in γ -alumina, a number of Y-type zeolites, and a silica–alumina catalyst system (8). For these samples, comprehensive and consistent assign- mentsto particular typesofsitesare made for allresonance lines in the 31 P MAS NMR spectra. Based on results from dehydroxylated γ -alumina,anewchemicalshiftassignment (37 ppm with respect to 85% phosphoric acid) was report- ed for a TMPO–Lewis-acid complex. Brønsted sites occur with a shift of50ppm and higher,and other formsofTMPO are also detected and characterized in the spectra. The assignments of 31 P resonances from molecules not directly associated with nearby 27 Al nuclei (such as crystalline or physisorbed TMPO species) were supported using 1 H/ 31 P/ 27 Al triple-resonance NMR methods. The concen- trations of Brønsted-acid sites as calculated from the NMR results were comparable with concentrations obtained from isopropylamine/temperature programmed desorp- tion (IPA/TPD) measurements.The most important results from this previous study were the positive identification of thechemicalshiftofaLewissite–TMPO complex(different from the reported shiftsofearlier studies),and the abilityto quantifythe number ofacid sitesafter titration with TMPO. However, in the previous study the only measurement 155 0021-9517/99 $30.00 Copyright c  1999 by Academic Press All rights of reproduction in any form reserved.