Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

Abstract

Two gas phase deuterium/hydrogen exchange reactions are described utilizing a simple inexpensive glass catalyst tube containing 0.5% Pd on alumina through which gas mixtures can be passed and products collected for analysis. The first of these exchange reactions involves H 2 + D 2 , which proceeds at temperatures as low as 77 K yielding a mixture that includes HD. Products are analyzed by 1 H NMR spectrometry. At low temperatures, this reaction requires a catalyst, but it proceeds without a catalyst at high temperature of a gentle flame. The second deuterium/hydrogen exchange reaction involves CH 4 + D 2 producing a series of isotopologues, methane-d x , x = 0−4, with product analysis by GC−MS and 1 H NMR spectrometry. This reaction only takes place in the presence of a catalyst at elevated temperatures due to the large energy of activation of the sp 3 -carbon-to-hydrogen bond. Two outcomes have been observed in the literature regarding D/H exchange and methane. Some catalysts and temperature conditions yield a single-exchange result, methane-d 1 . Others yield multiple exchange results, such as we observe with our catalyst. The single exchange outcome is associated with lower temperatures. Two mechanisms, one by Kemball (1959) and one by Frennet (1974), have been put forth to explain single and multiple exchange outcomes. We discuss our results in the context of these mechanisms. Interested readers could develop a research experience for undergraduate chemistry students based on the openended experiments presented here.

Unsupported Nanoporous Palladium Catalyst for Highly Selective Hydrogenation of Carbon Dioxide and Sodium Bicarbonate into Formate

“…The partial 1 H NMR spectrum of deuterium‐hydrogen exchange experiment is shown in Figure 6. The new peak at 4.62 ppm was assigned to molecular H 2 (CDCl 3 ) and molecular HD (CDCl 3 ) appears as a triplet, δ =4.58 ppm ( J HD =42.8 Hz), which was similar to that reported by Mattson et al [29] . H 2 gas was produced through the formation of DH generated via the heterolytic cleavage of D 2 .…”

Gas phase 1H NMR studies and kinetic modeling of dihydrogen isotope equilibration catalyzed by Ru-nanoparticles under normal conditions: dissociative vs. associative exchange

“…7,11 On the other hand, supported metal nanoparticles are useful catalysts for heterogeneous reactions. [12][13][14] Solid metal nanoparticles or colloids with diameters of 1-100 nm have also been used to catalyze hydrogenations or other reactions, most often at normal pressures, temperatures and in the presence of solvents. [15][16][17][18][19] Such nanoparticles consist of an inner core of metal atoms embedded in and stabilized by organic ligands, either functionalized molecules or polymers.…”

Investigating the Mechanism of Alkyne Hydrogenation through an Open-Ended, Inquiry-Based Undergraduate Research Project Exploring Heterogeneous Catalysis

“…Carbon–hydrogen bond activation for saturated alkanes does occur but only at high temperatures, so F → E is not a concern. For example, D–H exchange for methane with this same catalyst requires a temperature of at least 300 °C …”

“…For example, D−H exchange for methane with this same catalyst requires a temperature of at least 300 °C. 18 ■ EXPERIMENTAL SECTION Apparatus This article describes the hydrogenation/deuteration of 1butyne and 1-butene under ordinary laboratory conditions (∼1 atm) using a homemade catalyst tube containing nanoparticle palladium particles on alumina. 19 Unless otherwise stated, the normal gas flow rate through the catalyst is 1 mL/s.…”