In Situ ¹H NMR Investigation of Hydrogen Adsorption on a Cu/MgO Catalyst

Abstract

Hydrogen adsorption on a Cu/MgO catalyst is investigated using in situ 1H NMR. The adsorption is largely homogeneous, demonstrating reasonable agreement with the Langmuir isotherm and only small variations in the frequency shift and spin−lattice relaxation time with increasing coverage. The catalyst is investigated under flowing gas conditions, and the hydrogen/deuterium exchange kinetics are studied. The activation energy for exchange is measured to be 96 kJ mol-1. The 1H variable-temperature NMR probe developed here and used for the in situ adsorption isotherm and the flowing gas experiments is also described.

Pairwise hydrogen addition in the selective semihydrogenation of alkynes on silica-supported Cu catalysts

“…High selectivity toward 1-butene (≥97%) was always observed (Table 1). Even though hydrogen adsorption on the Cu surface is dissociative, 37,38 PHIP effects were detected in 1 H NMR spectra not only for vinylic protons of 1-butene but also for protons of its ethyl moiety as a result of spontaneous transfer of polarization in the Earth's magnetic field (Fig. 1b and c).…”

Kenneth John Packer. 18 May 1938—18 September 2021

“…For the following eight years, up to his retirement, he continued investigations of fluid flow in rocks, using the Bruker CXP-200B brought from BPR (figure 6), and revisited his earlier work on hydrogen chemisorption on supported metal catalysts, collaborating again with Mike Chesters to continue their work on model silica-supported platinum catalysts. An NMR probe was developed that could accommodate a sample volume of 7 cm 3 , to fit a super-wide-bore magnet, representing a tenfold increase in sample size over previous experiments (61). The improved quality of 1 H NMR spectra, coupled with careful quantitative measurement of hydrogen coverage, confirmed a model linking strongly adsorbed hydrogen to a 1 H resonance with a negative Knight shift and weakly adsorbed hydrogen to a 1 H resonance with a positive Knight shift.…”