Grain Reconstruction of Palladium and Palladium-Nickel Alloys for Platinum Catchment

Platinum-rhodium gauzes are frequently used to catalyse the high temperature ammonia oxidation step for production of synthetic nitrogen-based fertilisers. The gauzes suffer from Pt loss in the form of platinum dioxide (PtO2), due to the highly exothermic nature of the oxidation reaction. Industrially this is mitigated by installing one or more palladium-nickel catchment gauzes directly downstream of the combustion gauzes, to capture the lost Pt. The Pd-Ni catchment gauzes undergo severe structural modification during operation. In this study, we undertake a systematic study in a laboratory-scale furnace system to determine the role of each of the constituent gases O2, H2O and PtO2 on the structural changes of the Pd-Ni gauzes. In addition, some samples are exposed to real industrial conditions in an ammonia combustion pilot plant reactor. Fresh and spent catchment gauzes are analysed by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and inductively coupled plasma mass spectroscopy/optical emission spectroscopy (ICP-MS/OES). By combining analysis of samples from furnace and pilot scale experiments, the main findings are that Pd-Ni gauzes undergo internal oxidation to nickel(II) oxide (NiO); which in the presence of steam results in Ni depletion and that PtO2 vapour causes severe grain reconstruction. Furthermore, in laboratory-scale experiments no significant Pd loss is observed, which is in contrast to observations from the pilot plant where the samples are exposed to real post-ammonia oxidation conditions. Pd loss is likely attributed to some gas species contained in the real post-ammonia oxidation gas stream.</jats:p

Mechanistic features for propane reforming by carbon dioxide over a Ni/Mg(Al)O hydrotalcite-derived catalyst

A 1.9 wt% Ni/Mg(Al)O hydrotalcite-derived catalyst is studied for the dry reforming of propane to synthesis gas at 600 ↓C and 1 atm. The catalyst showed limited initial deactivation and then was exceptionally stable throughout a 34-day test. Catalyst characterization indicates that the carrier material consists of a mixed Mg(Al)O phase before and after testing, and that carbonate forms on the support surface under dry reforming conditions. The Ni particles are in close contact with, and partially decorated by, the basic support. No carbon whisker formation is obsd. by transmission electron microscopy after catalytic testing. Alternating pulse expts. in a Temporary Anal. of Product-II (TAP-II) reactor system indicate that CO2 is associatively adsorbed on the basic Mg(Al)O carrier and acts as a permanent source of oxygen species for the Ni metal. Propane reacts rapidly with Ni-O species to form CO and H2O. Under TAP conditions, reduced Ni reacts gradually with carbonate from the support to give Ni-O species and CO

Magnetic structure of Ce3TiBi5 and its relation to current-induced magnetization

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Microscopic Origin of Reduced Magnetic Order in a Frustrated Metal

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