Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma

The performance of CO oxidation over plasmonic Au/TiO2 photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO2, an O2 and Ar mixture gas as a discharge gas was employed to activate Au/TiO2. The photocatalytic activity in CO oxidation over activated Au/TiO2 was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O2 content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO2 rises rapidly at first and then remains constant at 75% when the O2 content is above 50%. Compared with the discharge gas of 10% and 30% O2/Ar, the sample activated by 50% O2/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO2 is discovered.

The Mitigation of CO Present in the Water–Gas Shift Reformate Gas Over IR-TiO2 and IR-ZrO2 Catalysts

CO hydrogenation and oxidation were conducted over Ir supported on TiO2 and ZrO2 catalysts using a feed mimicking the water–gas shift reformate stream. The influence of the support interaction with Ir and the catalysts’ redox and CO chemisorption properties on activity and selectivity were evaluated. Both catalysts oxidised CO to CO2 in the absence of H2, and a conversion of 70% was obtained at 200 °C. For the CO oxidation in the presence of H2 over these catalysts, the oxidation of H2 was favoured over CO due to H2 spillover occurring at the active metal and support interface, resulting in the formation of interstitials catalysed by Ir. However, both catalysts showed promising activity for CO hydrogenation. Ir-ZrO2 was more active, giving 99.9% CO conversions from 350 to 370 °C, with high selectivity towards CH4 using minimal H2 from the feed. Furthermore, results for the Ir-ZrO2 catalyst showed that the superior activity compared to the Ir-TiO2 catalyst was mainly due to the reducibility of the support and its interaction with the active metal. Controlling the isoelectric point during the synthesis allowed for a stronger interaction between Ir and the ZrO2 support, which resulted in higher catalytic activity due to better metal dispersions, and higher CO chemisorption capacities than obtained for the Ir-TiO2 catalyst.

Effects of Cobalt and Chromium Loadings to The Catalytic Activities of Supported Metal Catalysts in Methane Oxidation

A series of alumina supported cobalt and chromium catalysts with different metal loadings were prepared by impregnation method. Six types of alumina supported cobalt and chromium catalysts contained 5 wt%, 10 wt%, and 15 wt% loadings were produced and tested in methane oxidation. The catalysts were characterized by using x-ray diffraction (XRD) and carbon monoxide chemisorption (CO chemisorption). The XRD results do not confirmed any features of cobalt and chromium metal. The metal sizes for both catalysts were larger in high loading as shown by CO chemisorption results. Methane conversion results showed that the conversion increases with increasing the metal loading, however supported chromium catalysts were higher in activities compared to supported cobalt catalysts. Thermal stability tests on 15 wt% Co/Al and 15 wt% Cr/Al catalyst showed that supported chromium catalyst is more stable and maintain the particle size due to its strong interaction with support, while supported cobalt catalyst decrease in methane conversion due to deactivation of the catalyst. Copyright © 2020 BCREC Group. All rights reserved

Correlation of Rh Particle Size with CO Chemisorption: Effect on the Catalytic Oxidation of MTBE

This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). During the synthesis, first, TiO2 was developed by the sol-gel method under acidic conditions. Second, Rh was deposited (1 wt %) by the incipient wetness impregnation method. Later, with the aim of controlling the particle size, the Rh/TiO2 materials were crystallized at different reduction conditions during 3 h heat treatment. The results obtained by TEM micrographs indicated that the average particle size varies between 1.0 and 8.1 nm, depending on the conditions of heat treatment. From the histogram analysis of each TEM micrograph, two correlations were made: (i) the gem-dicarbonyl interaction was typical of Rh particles ≤ 1.5 nm, and (ii) a linear interaction, bridged interaction and dentate interaction were observed in particles ≥ 1.6 nm. The gem-dicarbonyl interaction (particle size ≤ 1.5 nm) was the most active in the oxidation reaction of MTBE.

Hydrogen Induced Cracking of a Dissimilar Weld in a Hydrogen Manufacturing Plant

A hydrogen manufacturing plant experienced circumferential cracking at the dissimilar weld on the outlet header. The outlet header was a cold wall design and the dissimilar weld was between HP40 modified and carbon ½ Mo steels. The resultant failure investigation found the cause to be hydrogen induced cracking of the dissimilar weld at the fusion boundary zone. The hydrogen was generated from the CO2 corrosion which occurred due to operating the tubes below the dew point and the hydrogen was trapped in the steel by the CO chemisorption onto the steel. The following paper outlines the failure investigation and the fitness for service conducted to maintain the running of the plant.