Although of pivotal importance in heterogeneous hydrogenation reactions, the amount of hydrogen on catalysts during reactions is seldom known. We demonstrate the use of neutron imaging to follow and quantify hydrogen containing species in Cu/ZnO catalysts operando during methanol synthesis. The steady-state measurements reveal that the amount of hydrogen containing intermediates is related to the reaction yields of CO and methanol, as expected from simple considerations of the likely reaction mechanism. The time-resolved measurements indicate that these intermediates, despite indispensable within the course of the reaction, slow down the overall reaction steps. Hydrogen-deuterium exchange experiments indicate that hydrogen reduction of Cu/ZnO nano-composites modifies the catalyst in such a way that at operating temperatures, hydrogen is dynamically absorbed in the ZnO-nanoparticles. This explains the extraordinary good catalysis of copper if supported on ZnO by its ability to act as a hydrogen reservoir supplying hydrogen to the surface covered by CO2, intermediates, and products during catalysis.

The catalytic activity of Pd surfaces towards hydrogen desorption was significantly improved by a nanometer-thin polytetrafluoroethylene (PTFE) layer, as shown by an enhancement in the permeability of a Pd membrane coated on the permeate side. The origin of this effect was found to be due to a lowering of the barrier for hydrogen desorption, as evidenced by a change in the rate-limiting mechanism of hydrogen permeation through the membrane from desorption (un-coated) to diffusion controlled. In situ X-ray photoelectron spectroscopy (XPS) revealed the electronic structure of the sputtered PTFE. Apart from C-F_n subunits (n=1, 2, 3), we found that nonsaturated carbon atoms became hydrogenated during hydrogen permeation, which was indicative of an interaction between Pd and PTFE. This interaction was weak; no Pd-F bonds were formed. We thus attributed the effect to an increase in the hydrophobicity of the surface by the porous PTFE layer and to a promoter effect of hydrogen desorption as a result of electrostatic interactions between chemisorbed hydrogen and physisorbed PTFE.

The structural, optical and dc electrical properties of Mg _xAl_1-x (0.2 ≤ x ≤ 0.9) gradient thin films covered with Pd/Mg are investigated before and after exposure to hydrogen. We use hydrogenography, a novel high-throughput optical technique, to map simultaneously all the hydride forming compositions and the kinetics thereof in the gradient thin film. Metallic Mg in the Mg_xAl_1-x layer undergoes a metal-to-semiconductor transition and MgH₂ is formed for all Mg fractions x investigated. The presence of an amorphous Mg-Al phase in the thin film phase diagram enhances strongly the kinetics of hydrogenation. In the Al-rich part of the film, a complex H-induced segregation of MgH₂ and Al occurs. This uncommon large-scale segregation is evidenced by metal and hydrogen profiling using Rutherford backscattering spectrometry and resonant nuclear analysis based on the reaction ¹H(¹⁵N, αγ)¹²C. Besides MgH₂, an additional semiconducting phase is found by electrical conductivity measurements around an atomic [Al]/[Mg] ratio of 2 (x = 0.33). This suggests that the film is partially transformed into Mg(AlH₄)₂ at around this composition.