Kinetic Evidence for the Influence of Subsurface Oxygen on Palladium Surfaces Towards CO Oxidation at High Temperatures

Abstract

Transient state kinetics of the catalytic oxidation of CO with O(2) on Pd-surfaces has been measured under isothermal conditions by using a molecular beam approach. Systematic studies were carried out as a function of reaction temperature and CO+O(2) composition. With sufficient kinetic evidence, we have demonstrated the positive influence of subsurface oxygen towards CO-adsorption and oxidation to CO(2) at high temperatures (600-900 K) on Pd-surfaces, and the likely electronic nature of the surface changes with oxygen in the subsurface. These studies also provide a direct proof for CO-adsorption with a significantly reactive sticking coefficient at high temperatures on Pd-surfaces exhibiting a significant subsurface O-coverage.

Interstitial modification of palladium nanoparticles with boron atoms as a green catalyst for selective hydrogenation

“…Teschner et al 5 have recently shown that interstitial C ( int C) produced in situ from adsorbed carbonaceous species at elevated temperature can be used to drastically alter the gas phase hydrogenation of alkynes. Subsurface O in Pd at high temperatures has also been demonstrated to be the kinetically active surface for CO oxidation in the high temperature regime 6,7 and the selective epoxidation of ethylene over silver catalysts is also thought to involve the subsurface oxygen atoms 8 . Apart from the b-hydride, it was not possible to experimentally isolate these interstitial occupied materials that were produced in situ, let alone of control and tune their content: The major technical difficulty to isolation being that these materials only exist under transient conditions in a small quantity at elevated temperatures and under an atmosphere of reactive gas.…”

“…The changes in lattice parameter and charge transfer between the host-guest may also alter the band structure, hence catalytic properties of the supported Pd metal [5][6][7][8][9][10] . It is therefore interesting to develop new Pd nanocatalysts modified with interstitial atoms as a greener alternative to Lindlar catalysts for selective hydrogenation reactions.…”

Sustainable and Near Ambient DeNOx Under Lean Burn Conditions: A Revisit to NO Reduction on Virgin and Modified Pd(111) Surfaces

“…The latter is mainly to simulate the calcination conditions carried out on supported Pd-based catalysts employed in the literature. − Ultraviolet photoelectron spectroscopy (UVPES), and XPS measurements were carried out with ambient pressure photoelectron spectrometer (APPES) in the presence of O 2 at relevant conditions to explore the electronic structure changes under experimental conditions. The present manuscript is part of our efforts in exploring the TWC reactions, such as CO oxidation and NO reduction with different reductants on Pd surfaces. ,− …”

Active Surfaces for CO Oxidation on Palladium in the Hyperactive State

“…Both metallic and oxide surfaces have been reported to play a key role. − Frenken et al , stated that the oxide surfaces are significantly more active for CO oxidation, while Goodman et al ,,, and Altmann et al reported the opposite results. Gopinath et al using molecular beam experiments demonstrated positive influence of the subsurface oxygen toward CO adsorption and oxidation to CO 2 at 600−900 K on a Pd surface. − On supported Pt catalysts, it was also found that partially oxidized Pt is significantly more active than a metallic Pt surface covered with CO . Additionally, the surface chemistry of oxygen interaction with Pd surfaces has been reported to be very complicated, mainly due to diffusion of oxygen into the subsurface and/or the formation of a bulk and metastable Pd x O y depending on the experimental conditions. − Furthermore, there is no oxygen poisoning observed with palladium in an auto converter, even under oxygen-rich conditions.…”