Sulfide Catalysis without Coordinatively Unsaturated Sites: Hydrogenation, Cis–Trans Isomerization, and H₂/D₂ Scrambling over MoS₂ and WS₂

Simple test reactions as ethene hydrogenation, 2-butene cis–trans isomerization and H₂/D₂ scrambling were shown to be catalyzed by MoS₂ and WS₂ in surface states which did not chemisorb oxygen and were, according to XPS analysis, saturated by sulfide species. This is a clear experimental disproof of classical concepts that require coordinative unsaturation for catalytic reactions to occur on such surfaces. It supports new concepts developed on model catalysts and by theoretical calculations so far, which have been in need of confirmation from real catalysis

Ionic Liquid-Assisted Sonochemical Preparation of CeO₂ Nanoparticles for CO Oxidation

CeO₂ nanoparticles were synthesized via a one-step ultrasound synthesis in different kinds of ionic liquids based on bis­(trifluoromethanesulfonylamide, [Tf₂N]⁻, in combination with various cations including 1-butyl-3-methylimidazolium ([C₄mim]⁺), 1-ethyl-2,3-dimethylimidazolium ([Edimim]⁺), butyl-pyridinium­([Py₄]⁺), 1-butyl-1-methyl-pyrrolidinium ([Pyrr₁₄]⁺), and 2-hydroxyethyl-trimethylammonium ([N₁₁₁₂OH]⁺). Depending on synthetic parameters, such as ionic liquid, Ce­(IV) precursor, heating method, and precipitator, formed ceria exhibits different morphologies, varying from nanospheres, nanorods, nanoribbons, and nanoflowers. The morphology, crystallinity, and chemical composition of the obtained materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and N₂ adsorption. The structural and electronic properties of the as-prepared CeO₂ samples were probed by CO adsorption using IR spectroscopy under ultrahigh vacuum conditions. The catalytic activities of CeO₂ nanoparticles were investigated in the oxidation of CO. CeO₂ nanospheres obtained sonochemically in [C₄mim]­[Tf₂N] exhibit the best performance for low-temperature CO oxidation. The superior catalytic performance of this material can be related to its mesoporous structure, small particle size, large surface area, and high number of surface oxygen vacancy sites

Rapid Microwave-Assisted Polyol Reduction for the Preparation of Highly Active PtNi/CNT Electrocatalysts for Methanol Oxidation

PtNi nanoparticle catalysts supported on oxygen functionalized carbon nanotubes were prepared by microwave-assisted polyol reduction using two different modes of irradiation, namely, continuous or pulsed irradiation. The influence of irradiation time or pulse number on catalyst structure and activity in methanol electrooxidation has been studied. Characterization was done with ICP-OES, XRD, TEM, XPS, and XAS to determine composition, morphology, crystal structural and chemical state. The electrocatalytic activity has been evaluated by cyclic voltammetry (CV) and chronoamperometry (CA). PtNi nanoparticles are present in alloy form and are well dispersed on the carbon nanotubes. Pt is in its metallic state, whereas Ni is present in metallic and oxidized form depending on the preparation conditions. The electrocatalytic activity both in terms of surface and mass specific activity is higher than that of the state-of-the-art-catalyst Pt/C (E-TEK). The enhancement of the electrocatalytic activity is discussed with respect to PtNi alloy formation and the resulting modification of the electronic properties of Pt by Ni in the alloy structure. The microwave assisted polyol method with continuous irradiation is more effective in the preparation of PtNi electrocatalysts both in terms of reaction time and activity than the pulsed microwave method

Efficient VO_<i>x</i>/Ce_1–<i>x</i>Ti_<i>x</i>O₂ Catalysts for Low-Temperature NH₃‑SCR: Reaction Mechanism and Active Sites Assessed by in Situ/Operando Spectroscopy

Supported V₂O₅/Ce_1–<i>x</i>Ti_<i>x</i>O₂ (3, 5, and 7 wt % V; <i>x</i> = 0, 0.1, 0.3, 0.5, 1) and bare supports have been tested in the selective catalytic reduction (SCR) of NO by NH₃ at different gas hourly space velocities (GHSVs) and were comprehensively characterized using XRD, pseudo in situ XPS, and UV–vis DRS as well as EPR and DRIFTS in in situ and operando mode. The best V/Ce_1–<i>x</i>Ti_<i>x</i>O₂ (<i>x</i> = 0.3, 0.5) catalysts showed almost 100% NO conversion and N₂ selectivity already at 190 °C with a GHSV value of 70000 h^–1, which belongs to the best performances observed so far in low-temperature NH₃-SCR of NO. The corresponding bare supports still converted around 80% to N₂ under the same conditions. On bare supports, SCR proceeds via a Langmuir–Hinshelwood mechanism comprising the reaction of adsorbed surface nitrates with adsorbed NH₃. On V/Ce_1–<i>x</i>Ti_<i>x</i>O₂, nitrate formation is not possible, and an Eley–Rideal mechanism is working in which gaseous NO reacts with adsorbed NH₃ and NH₄⁺. Lewis and Brønsted acid sites, though adsorption of NH₃, do not scale with the catalytic activity, which is governed rather by the redox ability of the materials. This is boosted in the supports by replacing Ce with the more redox active Ti and in catalysts by tight connection of vanadyl species via O bridges to the support surface forming −Ce–O–V­(O)–O–Ti– units in which the equilibrium valence state of V under reaction conditions is close to +5