We systematically investigated the role of surface modification of nanoparticles catalyst in alkyne hydrogenation reactions and proposed the general explanation of effect of surface ligands on the selectivity and activity of Pt and Co/Pt nanoparticles (NPs) using experimental and computational approaches. We show that the proper balance between adsorption energetics of alkenes at the surface of NPs as compared to that of capping ligands defines the selectivity of the nanocatalyst for alkene in alkyne hydrogenation reaction. We report that addition of primary alkylamines to Pt and CoPt(3) NPs can drastically increase selectivity for alkene from 0 to more than 90% with ~99.9% conversion. Increasing the primary alkylamine coverage on the NP surface leads to the decrease in the binding energy of octenes and eventual competition between octene and primary alkylamines for adsorption sites. At sufficiently high coverage of catalysts with primary alkylamine, the alkylamines win, which prevents further hydrogenation of alkenes into alkanes. Primary amines with different lengths of carbon chains have similar adsorption energies at the surface of catalysts and, consequently, the same effect on selectivity. When the adsorption energy of capping ligands at the catalytic surface is lower than adsorption energy of alkenes, the ligands do not affect the selectivity of hydrogenation of alkyne to alkene. On the other hand, capping ligands with adsorption energies at the catalytic surface higher than that of alkyne reduce its activity resulting in low conversion of alkynes.

NCT01926028.

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The many studies that have been conducted on water adsorption on zeolites were carried out in "adsorption" mode, from adsorption isotherms or single-point measurements, with the samples being first degassed at high temperature, and then exposed to water vapor at variable partial pressure. Here, we report Thermogravimetric Analysis (TGA) studies of HZSM-5 saturated with water at room temperature, thus studying water adsorption in "desorption" mode. TGA was used to ascertain the amount of water remaining as a function of the pretreatment temperature, and to identify the temperature at which one water molecule per framework Al atom persists. 1860 Ison and Gorte studied water adsorption on a HZSM-5 with SAR = 70 via temperature programmed desorption (TPD), thermogravimetric analysis (TGA), and transmission infrared spectroscopy (IR), [8] and found clusters of up to 5.3 waters per Al at 306 K. An adsorption energy of 12.1 kcal/mol and 8.2 kcal/mol was calculated for 0.7 and 2.0 waters per Al, respectively, leading to the conclusion that the first water forming a hydronium ion, H 3 O + , at the acid sites is more strongly held than subsequent waters that form clusters. Eckstein et al., also reported that water adsorption on HZSM-5 is proportional to the Al content showing a maximum of 7 waters per Brønsted acid site. [9] All these previous works studied water in "adsorption" mode, from adsorption isotherms or single-point measurements whereby the samples were first degassed at high temperature and then exposed to water vapor at variable partial pressure. Herein, we report TGA studies of HZSM-5 samples of varying SAR saturated with water at room temperature using tempera-Carlos Bornes is a PhD student at CICECO -Aveiro Institute of Materials, University of Aveiro. He obtained his M. Sc. in 2017 from the Department of Chemistry, University of Aveiro, working on the characterization of zeolites by solid-state NMR spectroscopic methods. His current line of research is the characterization of the acid properties of zeolites using solid-state NMR and computational methods. Jeffrey Amelse received a B.Mark Peacock works at BP since 1998 in a range of catalysis development roles & focuses on advanced catalyst characterisation since 2008, primarily focusing on powder X-ray diffraction, In-situ pXRD as well as thermal analysis (TGA) and combustion elemental analysis. His experience covers a range of zeolite catalysts, binders as well and many heterogeneous metal/ metal oxide based systems. Christopher L. Marshall is a senior research chemist in the Catalysis Science Group of the Chemical Sciences and Engineering Division at Argonne. His research concentrates on the synthesis, testing and in situ characterization of refining, chemical and biomass conversion catalysts. Synthesis work has recently concentrated on the use of atomic layer deposition for stabilization and improved performance of supported catalysts. Michael M. Schwartz, now retired, obtained his Ph.D. (1970) at Florida State University. . His current research inter...