Search

The addition of gold, by deposition precipitation, to a mixed copper manganese oxide catalyst (Hopcalite) has been studied for ambient temperature carbon monoxide oxidation. The deposition of gold on the catalyst surface enhanced the activity of the Hopcalite. The catalyst containing 1 wt% gold was the most active and showed higher activity than Hopcalite containing 0.5 and 2 wt% gold. It is expected that the introduction of gold will introduce new active sites to the Hopcalite that are associated with the gold nanoparticles. However, gold addition also increased the reducibility of the catalyst significantly compared to unmodified Hopcalite, and the most easily reduced catalyst was the most active, indicating that the lability of lattice oxygen was an important factor influencing activity. Graphical Abstract: The activity of a copper-manganese oxide catalyst for ambient temperature CO oxidation is significantly promoted by the addition of gold using deposition precipitation.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A fluidizable, Ni/Mg/K/AD90(90% α-Al2O3) catalyst was evaluated in a pilot-scale study with oak-derived syngas for tar and methane reforming at 900 °C. The catalyst was operated in a semi-batch mode for ten individual reaction cycles, each separated by a regeneration protocol consisting of steaming followed by H2 reduction. During the experiment, subsequent reaction cycles showed a decrease in activity as indicated by decreased initial methane conversion. During each reaction cycle, H2S poisoning was the dominant deactivation mechanism, while coking was deemed to be minor in comparison. Catalyst characterization by XRD and TPR suggest that the loss of activity for subsequent reaction cycles coincides with the formation of a NiAl2O4 species that is not fully reduced under process conditions, which in turn results in a decreased number of potential metallic nickel (Ni0) sites available for hydrocarbon steam reforming. An increase in nickel crystallite size with time-on-stream was also observed using XRD, indicating that sintering may also play a role in loss of catalyst activity, although this is not considered the primary deactivation mechanism because activity loss was observed even when nickel crystallite sizes remained nearly constant. [ABSTRACT FROM AUTHOR]

This study tested the selectivity and sustainability of an alumina-supported Pd–In bimetallic catalyst for nitrate reduction with H2 in a continuous-flow packed-bed reactor in the presence of: (i) dissolved oxygen (DO), an alternative electron acceptor to nitrate, (ii) variable NO3 −:H2 influent loadings, and (iii) the presence of a known foulant, sulfide. The sustainability of the catalyst was promising, as the catalyst was found to be stable under all conditions tested with respect to metal leaching. The presence of DO at concentrations typical of treatment conditions will increase H2 demand for NO3 − reduction, but has no negative impact on the selectivity of the catalyst. Under optimal conditions, i.e., a pH of 5.0 and a high NO3 −:H2 influent loading, low NH3 selectivity (5%) was achieved for extended periods (36 days), resulting in sustained levels of NH3 that approached the European legal limit. The biggest challenge to the sustainability of the catalyst was the addition of sulfide, that initially increased NH3 selectivity and ultimately resulted in complete deactivation of the catalyst. Further work is required to identify regeneration methods to restore sulfide-fouled catalyst activity and selectivity; however, the most effective use would be to remove sulfide prior to catalytic treatment. [ABSTRACT FROM AUTHOR]

Pd/HZSM-5 catalyst prepared via glow discharge plasma reduction followed by calcination thermally showed enhanced stability for methane combustion. In order to investigate the plasma catalyst preparation mechanism, oxygen glow discharge, initiated at room temperature, has been employed for reduction of Pd/HZSM-5 catalyst. The catalyst characterization using XRD and XPS analyses demonstrates that oxygen glow discharge plasma is also able to reduce Pd/HZSM-5 catalyst. This suggests that the electronic effect plays an important role in the treatment of catalyst using glow discharge. This also confirms that the thermal effect of the glow discharge reduction can be ignored. A highly durable catalyst for methane combustion has been obtained from calcination of the glow discharge reduced sample. [ABSTRACT FROM AUTHOR]

In order to improve the catalytic performance of supported-Ir catalysts for the selective reduction of NO with CO, the effect of H2 was investigated. While adding H2 showed no or negative effect on NO conversion on Ir/SiO2, Ba/Ir/SiO2 and Ir/WO3/SiO2 catalysts, the activity of Ba-doped Ir/WO3/SiO2 catalyst for NO reduction was significantly increased by H2 addition. The role of H2 was found to stabilize the catalytically active Ir-WO x sites during the reaction. [ABSTRACT FROM AUTHOR]

An unusual behavior was observed during experiments conducted at 371 and 465 °C with a commercial NOX storage/reduction catalyst: the outlet NOX concentration during the trapping phase reached a cycle minimum after regeneration, increased for 20–30 s, as expected, but then surprisingly decreased, indicating the catalyst had become more efficient in trapping the entering NOX. The results reported in this letter indicate that this phenomenon was caused by a superposition of two factors: a substantial exotherm associated with the regeneration event from reductant reacting with surface oxygen species and a negative impact of an evolving temperature profile on the dynamic NOX storage capacity. [ABSTRACT FROM AUTHOR]

The ability of H2S to reduce NO in a fixed bed reactor using a γ-alumina catalyst was studied with the objective of generating new methods for conversion of NO to N2. Compared to the homogenous reaction of NO with H2S, the catalyzed reaction showed improved conversions of NO to N2. Using a gas space velocity of 1000 h−1 and a feed of 1% NO and 1% H2S in argon, it was found that the conversion of NO to N2 was complete at 800 °C. This result compared to a 38% conversion of NO to N2 for the homogeneous gas phase reaction at 800 °C. At temperatures below 800 °C, a short fall in the nitrogen balance was discovered when the γ-alumina was employed as a catalyst. This discrepancy was explained by conversion of NO to NH3 and subsequent reaction of the NH3 with any SO2 in the system to form ammonium sulfur oxy-anion salts. This suggestion is supported by the finding that when larger amounts of H2S were used relative to NO, more NH3 was formed together in tandem with lower N2 mass balances. Several reaction pathways have been proposed for the catalytic reduction of NO by H2S. [ABSTRACT FROM AUTHOR]