Physical Organic Chemistry of Solid Acids:  Lessons from in Situ NMR and Theoretical Chemistry

Abstract

After 18 months as a research associate with Professor Gary Maciel at Colorado State University, he joined the faculty of Texas A&M University in 1984. His research interests include demanding applications of NMR spectroscopy to important problems in all areas of chemistry, especially reactive intermediates. Theoretical chemistry is a recent interest. John B. Nicholas was born in Hinsdale, IL, in 1954. After a career as a professional musician, he turned to the sciences. He received his B.S. in biochemistry from Illinois Benedictine College in 1986. He obtained his Ph.D. in physical chemistry from the University of Illinois at Chicago under the direction of Anton J. Hopfinger.

Styrene and styrene dimer derivatives, cyclohexene, tert-butylbenzene and cumene as test reactions for acid strength measurements of crystalline and amorphous silica-aluminas, sulfated oxides and Amberlyst

“…The values of acid strength (H O ) of acid solutions were estimated at -10.5, -15.07 and -26, while the results were as follows for solid acids: HM -13.7, HZSM-5 -10, HY -9 and SZ -18.5. It seems that the obtained results overestimated the acid strengths of zeolites, which, according to Haw [20], did not exceed -7.46 H O units.…”

“…The basis of these measurements is the correlation of d 13 C chemical shifts with calculated deprotonation energy of acid sites [32]. Some results are presented below [20,32,33] [9] reported, in the case of acetone applied as probe molecule, that the acid strength of HZSM-5 was in the proximity of that of 70 % H 2 SO 4 (H O = -5.8) and higher than the values for HY and HX zeolites as well as SZ. Moreover, the observed 13 C chemical shift value for adsorbed acetone is a mean of the values of adsorption on several acid sites of varying acid strengths.…”

Recent developments in solid-state NMR spectroscopy of crystalline microporous materials

“…7,8,10 Catalysis may occur at Brønsted sites, e.g., Al-OH-Si in zeolites or M-OH-P in phosphates, or at Lewis sites (generally at under-coordinated cations that can accept acetone is also very sensitive to the presence of acid sites, with higher shifts observed for more acidic sites. 7,8,110 Characterising the position, strength, type and distribution of acid sites is the first (and perhaps most vital) step in understanding the catalytic properties of a material.…”

Decomposition of styrene dimers: the influence of the acid strength of the catalyst

“…In PS cracking products, styrene oligomers as well as benzene, toluene, styrene, ethylbenzene, cumene and indane, indene and naphthalene derivatives were observed [3][4][5]. Haw [6] reported that the cyclic styrene dimer adsorbed in the structure of HZSM-5 at 373 K dealkylates into benzene and methylindyl cation, which forms naphthalene at elevated temperature.…”

“…The most used such methods are based on Hammett indicator adsorption [6,7], adsorption of probe molecules examined with calorimetric [7,8], thermoprogrammed desorption (TPD) [7,9,10] and NMR [6] measurements. The acid strength can be also estimated by means of the test reaction method [11,12].…”