Cu model catalyst dynamics and CO oxidation kinetics studied by simultaneous in situ UV-Vis and mass spectroscopy

The oxidation state of Cu nanoparticles during CO oxidation in CO + O2 gas mixtures was sensitively monitored via localized surface plasmon resonances. A microreactor, equipped with in situ UV-vis and mass spectrometry, was developed and used for the measurements. Cu nanoparticles of ∼30 nm average diameter were supported on optically transparent, planar quartz wafers. The aim of the study is 2-fold: (i) to demonstrate the performance and usefulness of the setup and (ii) to use the combined strength of model catalysts and in situ measurements to investigate the correlation between the catalyst oxidation state and its reactivity. Metallic Cu is significantly more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase is only maintained under conditions where close to full oxygen conversion is achieved. This implies that kinetic measurements, aimed at determining the apparent activation energy for metallic Cu under realistic steady-state conditions, are difficult or impossible to perform

Role of ZnO and CeOx in Cu-Based model catalysts in activation of h2O and CO2 dynamics studied by in situ ultraviolet−Visible and x‑ray photoelectron spectroscopy

Flat model and powder Cu, ZnO/Cu, and CeOx/Cu catalysts were studied by focusing on the role of the oxide phase as a promoter in the water gas shift (WGS) and its reverse reaction (RWGS). Activity measurements of the powder catalysts showed that both oxides enhance Cu reactivity, with CeOx/Cu being more active than ZnO/Cu in the WGS reaction. In situ ultraviolet−visible spectroscopy, exploiting the localized surface plasmon resonances of metallic Cu nanoparticles, together with X-ray photoelectron spectroscopy was then used to elucidate the origin of the enhanced reactivity on flat model catalysts. These experiments showed that ZnO and CeOx promote H2O and CO2 dissociation, leading to oxidation of the Cu nanoparticles. CeOx performs better in this respect than ZnO. This is important because the reactivity in the WGS and RWGS reactions is related to the ability to activate H2O and CO2. The Ce3+ ions are identified as the most efficient sites for H2O and CO2 dissociation, while Cu0 keeps Ce3+ stable by promoting reduction of Ce4+ during the dissociation process. In this sense, the CeOx/Cu catalyst forms a bifunctional catalyst, which is more active in the (R)WGS than CeOx and Cu catalysts separately

Inhibit the formation of toxic methylphenolic by-products in photo-decomposition of formaldehyde-toluene/xylene mixtures by Pd cocatalyst on TiO2

Photocatalytic removal of single volatile organic compounds (VOCs) has been widely investigated; however, photodecomposition of VOC mixtures has been rarely addressed, which may bring safety doubts in indoor air purification due to possible formation of harmful compounds. Here we show that in photocatalytic oxidation of formaldehyde–toluene and formaldehyde–xylene mixtures, the introduction of Pd cocatalyst on TiO2 photocatalyst successfully inhibits the formation of toxic methylphenols, thus promoting the complete mineralization of VOC mixtures into CO2 via the harmless benzaldehyde intermediates. Mechanistic analysis reveals that the loading of Pd cocatalyst effectively removes the inherent surface −OH groups of TiO2, which significantly promotes the activation of O2 into radical dotOH radicals. The Pd cocatalyst also directs the radical dotOH radicals to attack the methyl group instead of the aromatic ring for the formation of benzaldehyde and its further oxidation to CO2, thus yielding a better overall photocatalytic performance

SiO2-supported Fe & FeMn colloids—Fischer-Tropsch synthesis on 3D model catalysts

A well-defined model catalyst constituting a compromise between high surface area, porous, industrial catalysts and a planar model catalyst has been developed. It allows for measurements of catalytic activity in micro reactors, where diffusion problems are kept at a minimum, while characterization both by surface science techniques and by bulk techniques can be applied. Monodisperse, non-porous SiO 2 microspheres with diameter 875 ± 25 nm have been synthesized, serving as the large area model support. These where then impregnated with pre-formed, monodisperse, colloidal Fe and FeMn nanoparticles resulting in a three-dimensional equivalent of a flat, Fe(-Mn)/SiO 2 model catalysts. Characterization with electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), before and after catalytic testing was performed. It was shown that the model catalysts can be used in Fischer-Tropsch synthesis experiments under industrially relevant conditions. The FTS experiments reveal that compared to the pure Fe catalyst, FeMn shows more stable activity, higher selectivity towards olefins and lower selectivity toward CH 4 and CO 2. Significant amounts of hydrocarbons on the catalyst surfaces and some minor indications of sintering were detected after the reaction. Formation of FeC x was detected for the Fe catalyst while no significant amounts could be seen on the Mn-promoted catalyst

Relevance of chemical vs electrochemical oxidation of tunable carbene iridium complexes for catalytic water oxidation

Based on previous work that identified iridium(III) Cp* complexes containing a C,N-bidentate chelating triazolylidene-pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C 5Me 5 –) as efficient molecular water oxidation catalysts, a series of new complexes based on this motif has been designed and synthesized in order to improve catalytic activity. Modifications include specifically the introduction of electron-donating substituents into the pyridyl unit of the chelating ligand (H, a; 5-OMe, b; 4-OMe, c; 4-tBu, d; 4-NMe 2, e), as well as electronically active substituents on the triazolylidene C4 position (H, 8; COOEt, 9; OEt, 10; OH, 11; COOH, 12). Chemical oxidation using cerium ammonium nitrate (CAN) indicates a clear structure-activity relationship with electron-donating groups enhancing catalytic turnover frequency, especially when the donor substituent is positioned on the triazolylidene ligand fragment (TOF max = 2500 h – 1 for complex 10 with a MeO group on pyr and a OEt-substituted triazolylidene, compared to 700 h – 1 for the parent benchmark complex without substituents). Electrochemical water oxidation does not follow the same trend, and reveals that complex 8b without a substituent on the triazolylidene fragment outperforms complex 10 by a factor of 5, while in CAN-mediated chemical water oxidation, complex 10 is twice more active than 8b. This discrepancy in catalytic activity is remarkable and indicates that caution is needed when benchmarking iridium water oxidation catalysts with chemical oxidants, especially when considering that application in a potential device will most likely involve electrocatalytic water oxidation

CCDC 1909359: Experimental Crystal Structure Determination

Related Article: Marta Olivares, Cornelis J. M. van der Ham, Velabo Mdluli, Markus Schmidtendorf, Helge Müller-Bunz, Tiny W.G.M Verhoeven, Mo Li, Hans J. W. Niemantsverdriet, Dennis G. H. Hetterscheid, Stefan Bernhard, Martin Albrecht, J. W. Hans Niemantsverdriet|2020|Eur.J.Inorg.Chem.|2020|801|doi:10.1002/ejic.20200009

CCDC 1909360: Experimental Crystal Structure Determination

Related Article: Marta Olivares, Cornelis J. M. van der Ham, Velabo Mdluli, Markus Schmidtendorf, Helge Müller-Bunz, Tiny W.G.M Verhoeven, Mo Li, Hans J. W. Niemantsverdriet, Dennis G. H. Hetterscheid, Stefan Bernhard, Martin Albrecht, J. W. Hans Niemantsverdriet|2020|Eur.J.Inorg.Chem.|2020|801|doi:10.1002/ejic.20200009

CCDC 1909363: Experimental Crystal Structure Determination

Related Article: Marta Olivares, Cornelis J. M. van der Ham, Velabo Mdluli, Markus Schmidtendorf, Helge Müller-Bunz, Tiny W.G.M Verhoeven, Mo Li, Hans J. W. Niemantsverdriet, Dennis G. H. Hetterscheid, Stefan Bernhard, Martin Albrecht, J. W. Hans Niemantsverdriet|2020|Eur.J.Inorg.Chem.|2020|801|doi:10.1002/ejic.20200009

CCDC 1909361: Experimental Crystal Structure Determination

Related Article: Marta Olivares, Cornelis J. M. van der Ham, Velabo Mdluli, Markus Schmidtendorf, Helge Müller-Bunz, Tiny W.G.M Verhoeven, Mo Li, Hans J. W. Niemantsverdriet, Dennis G. H. Hetterscheid, Stefan Bernhard, Martin Albrecht, J. W. Hans Niemantsverdriet|2020|Eur.J.Inorg.Chem.|2020|801|doi:10.1002/ejic.20200009

CCDC 1909355: Experimental Crystal Structure Determination

Related Article: Marta Olivares, Cornelis J. M. van der Ham, Velabo Mdluli, Markus Schmidtendorf, Helge Müller-Bunz, Tiny W.G.M Verhoeven, Mo Li, Hans J. W. Niemantsverdriet, Dennis G. H. Hetterscheid, Stefan Bernhard, Martin Albrecht, J. W. Hans Niemantsverdriet|2020|Eur.J.Inorg.Chem.|2020|801|doi:10.1002/ejic.20200009