Choice of precipitant and calcination temperature of precursor for synthesis of NiCo2O4 for control of CO-CH4 emissions from CNG vehicles

Compressed natural gas (CNG) is most appropriate an alternative of conventional fuel for automobiles. However, emissions of carbon-monoxide and methane from such vehicles adversely affect human health and environment. Consequently, to abate emissions from CNG vehicles, development of highly efficient and inexpensive catalysts is necessary. Thus, the present work attempts to scan the effects of precipitants (Na₂CO₃, KOH and urea) for nickel cobaltite (NiCo₂O₄) catalysts prepared by co-precipitation from nitrate solutions and calcined in a lean CO-air mixture at 400°C. The catalysts were used for oxidation of a mixture of CO and CH₄ (1:1). The catalysts were characterized by X-ray diffractometer, Brunauer-Emmett-Teller surface-area, X-ray photoelectron spectroscopy; temperature programmed reduction and Scanning electron microscopy coupled with Energy-Dispersive X-Ray Spectroscopy. The Na₂CO₃ was adjudged as the best precipitant for production of catalyst, which completely oxidized CO-CH₄ mixture at the lowest temperature (T₁₀₀=350°C). Whereas, for catalyst prepared using urea, T₁₀₀=362°C. On the other hand the conversion of CO-CH₄ mixture over the catalyst synthesized by KOH limited to 97% even beyond 400°C. Further, the effect of higher calcination temperatures of 500 and 600°C was examined for the best catalyst. The total oxidation of the mixture was attained at higher temperatures of 375 and 410°C over catalysts calcined at 500 and 600°C respectively. Thus, the best precipitant established was Na₂CO₃ and the optimum calcination temperature of 400°C was found to synthesize the NiCo₂O₄ catalyst for the best performance in CO-CH₄ oxidation.

Can molten carbonate be a non-metal catalyst for CO oxidation?

For the first time, we have examined molten carbonate as a non-metal catalyst for CO oxidation in the temperature range of 300–600 °C.

In situgenerated catalyst: copper(ii) oxide and copper(i) supported on Ca2Fe2O5for CO oxidation

Two sets of copper oxide–brownmillerite Ca₂Fe₂O₅catalysts are prepared and studied for CO oxidation.

Migration of copper species in CexCu1−xO2 catalyst driven by thermal treatment and the effect on CO oxidation

A Cu-doped CeO₂ solid solution was constructed by co-precipitation and additional acid treatment to investigate the behavior of doped copper under thermal treatment.

An atomic-level insight into the basic mechanism responsible for the enhancement of the catalytic oxidation of carbon monoxide on a Cu/CeO2 surface

Reaction mechanism of CO molecules onto a Cu/CeO₂ surface and morphological changes.

CO oxidation on mesoporous SBA-15 supported CuO–CeO2 catalyst prepared by a surfactant-assisted impregnation method

A series of mesoporous SBA-15 supported CuO–CeO₂ catalysts were prepared by a surfactant-assisted impregnation method with PEG 200 as the surfactant.

Co3O4 morphology in the preferential oxidation of CO

Different morphologies of Co₃O₄ were synthesized and tested for their performance in the preferential oxidation (PrOx) of carbon monoxide to investigate the effect of preferentially exposed crystal planes.

The absence of a gap state and enhancement of the Mars-van Krevelen reaction on oxygen defective Cu/CeO2 surfaces

We report a detailed first-principles analysis of the electronic structures of oxygen defective CeO2 and Cu/CeO2 surfaces aimed at elucidating the disappearance of the gap state of defective CeO2 when a Cu atom is added at the surface. The top of the valence band of Cu/CeO2 originates from the O 2p states around this Cu atom. We show that this redistribution of electronic states at the defective Cu/CeO2 surface enhances the reactivity of the surface O atoms. Indeed, dynamical simulations show an acceleration of catalytic NO oxidation occurring via the Mars-van Krevelen mechanism mediated by these highly reactive oxygens.

Catalytic oxidation of aromatic amines to azoxy compounds over a Cu–CeO2 catalyst using H2O2 as an oxidant

Highly dispersed Cu-nanoparticles supported on nanocrystalline CeO₂ were prepared which showed good catalytic activity toward selective oxidation of aromatic amines.

Boosting soot combustion efficiencies over CuO–CeO2 catalysts with a 3DOM structure

A CuO–CeO₂ catalyst with a well-defined 3DOM structure exhibited superior catalytic activity for soot combustion compared to its 3DOM CeO₂ counterpart.

The promoter effect of potassium in CuO/CeO2 systems supported on carbon nanotubes and graphene for the CO-PROX reaction

Improved performance of catalysts promoted with K was obtained in the CO-PROX reaction.

CeO2 decorated CuO hierarchical composites as inverse catalyst for enhanced CO oxidation

CeO₂ decorated CuO hierarchical composites were prepared and was used as inverse catalyst for enhanced CO oxidation.

Nanoparticle catalyst preparation using pulsed arc plasma deposition

A novel nanoparticle preparation technique using pulsed arc plasma deposition has been developed as a dry catalyst preparation process in complete contrast to conventional wet processes.

Low-temperature CO oxidation on CuO/CeO2catalysts: the significant effect of copper precursor and calcination temperature

The performance of CuO/CeO₂catalysts for CO oxidation strongly depends on the type of copper precursor and the calcination temperature.

CO oxidation activity of thermally stable Fe–Cu/CeO2 catalysts prepared by dual-mode arc-plasma process

Fe–Cu bimetal nanoparticles were prepared by the dual-mode arc-plasma process. The CO oxidation activity of Fe–Cu/CeO₂ was enhanced by thermal aging at 900 °C. CO oxidation over aged Fe–Cu/CeO₂ proceeded via the Mars–van Krevelen mechanism.

Structural features and catalytic performance in CO preferential oxidation of CuO–CeO2 supported on multi-walled carbon nanotubes

MWCNT supported CuO–CeO₂ catalysts show enhanced performance in CO-PROX due to unusual structure features induced by interactions between metal oxides and MWCNT.

Gold atoms stabilized on various supports catalyze the water-gas shift reaction

For important chemical reactions that are catalyzed by single-site metal centers, such as the water-gas shift (WGS) reaction that converts carbon monoxide and water to hydrogen and carbon dioxide, atomically dispersed supported metal catalysts offer maximum atom efficiency. Researchers have found that for platinum metal supported on ceria and doped ceria in the automobile exhaust catalyst, atomic Pt-Ox-Ce species are the active WGS reaction sites. More recently, preparations of gold at the nanoscale have shown that this relatively "new material" is an active and often more selective catalyst than platinum for a variety of reactions, including the WGS reaction. The activity of gold is typically attributed to a size effect, while the interface of gold with the support has also been reported as important for oxidation reactions, but exactly how this comes about has not been probed satisfactorily. Typical supported metal catalysts prepared by traditional techniques have a heterogeneous population of particles, nanoclusters, subnanometer species, and isolated atoms/ions on the support surfaces, making the identification of the active sites difficult. Both we and other researchers have clearly shown that gold nanoparticles are spectator species in the WGS reaction. Evidence has now amassed that the gold active site for the WGS reaction is atomic, that is, Au-Ox species catalyze the reaction, similar to Pt-Ox. In this Account, we review the relevant literature to conclude that the intrinsic activity of the Au-Ox(OH)-S site, where S is a support, is the same for any S. The support effect is indirect, through its carrying (or binding) capacity for the active sites. Destabilization of the gold under reducing conditions through the formation of clusters and nanoparticles is accompanied by a measurable activity loss. Therefore, it is necessary to investigate the destabilizing effect of different reaction gas mixtures on the gold atom sites and to consider regeneration methods that effectively redisperse the gold clusters into atoms. For gold catalysts, we can remove weakly bound clusters and nanoparticles from certain supports by leaching techniques. Because of this, we can prepare a uniform dispersion of gold atoms/ions strongly bound to the support surface by this two-step (loading followed by leaching) approach. Presently, one-step preparation methods to maximize the number of the single atom sites on various supports need to be developed, specific to the type of the selected support. Often, it will be beneficial to alter the surface properties of the support to enhance metal ion anchoring, for example, by shape and size control of the support or by the use of light-assisted deposition and anchoring of the metal on photoresponsive supports. Because of their importance for practical catalyst development, synthesis methods are discussed at some length in this Account.