A radiotracer technique for adsorption and catalysis studies: Application to 14C-benzene chemisorption and rehydrogenation on Pt(111)

Abstract

A radiotracer counting system was developed for adsorption and catalysis studies in ultrahigh vacuum using small area, single crystal surfaces. The counting system utilizes a rugged, compact, and rotatable surface barrier detector with a sensitivity sufficient to detect about lxlo 12 molecules containing carbon-14. The operating characteristics and performance of this counting system are discussed along with its application to studies of 14 c-benzene chemisorption and rehydrogenation on the (111) crystal face of platinum.

Deuterium exchange reactions of isobutane, n-hexane and n-heptane catalyzed over platinum single crystal surfaces

“…Atomic surface structures for these samples are compared in Figure 1. The (10,8,7) surface has (111) terraces averaging 15.1 A (about five platinum atoms) in width, separated by monatomic steps with (310) orientation.…”

“…The initial product distributions (a=mole%) were then n computed where ai=l0 2 di/ dj, and n=lO, 14, or 16 for isobutane, n-hexane, and j=l n-heptane, respectively. From these initial distributions, the mean content of n deuterium atoms per exchanged molecule, M=lo-2 i: j aj , was evaluated.-j=l Results n-Hexane-Dz Exchange Kinetics: Isotopic exchange reactions between n-hexane and deuterium gas were catalyzed over the flat (111) and kinked (10,8,7) crystal faces of platinum at temperatures between 508 and 658 K with total pressures ranging from 100 to 620 torr. Total product accumulation curves measured as a function of reaction time for Pt(l0,8,7) with D2/HC=lO, and Ptot=220 torr are shown at several temperatures in Figure 2.…”

“…Materials: The exchange reactions were studied over flat (111) and kinked (10,8,7) platinum single crystal surfaces that were prepared and characterized (±1°) in the usual manner7. Atomic surface structures for these samples are compared in Figure 1.…”

“…This paper describes reaction kinetics and product distributions that were measured for n-hexane, n-heptane, and isobutane deuterium exchange reactions catalyzed over the flat (111) and kinked (10,8,7) platinum single crystal surfaces. The studies were carried out near atmospheric pressure at temperatures between 500 and 650 K. Under these conditions hydrocarbon conversion to hydrogenolysis, isomerization, and cyclization products occurred simultaneously with deuterium exchange.…”

A radiotracer (14C) and catalytic study of thiophene hydrodesulfurization on the clean and carbided Mo(100) single-crystal surface

“…The detector and the data collection system have been described previously. 16 The detection system consists of an Ortec silicon surface barrier detector recessed in a liquid nitrogen cooled copper jacket and connected to a rotatable feedthrough.…”