Formation Mechanism of a Nano‐Ring of Bismuth Cations and Mono‐Lacunary Keggin‐Type Phosphomolybdate

A new hetero‐bimetallic polyoxometalate (POM) nano‐ring was synthesized in a one‐pot procedure. The structure consists of tetrameric units containing four bismuth‐substituted monolacunary Keggin anions including distorted [BiO₈] cubes. The nano‐ring is formed via self‐assembly from metal precursors in aqueous acidic medium. The compound (NH₄)₁₆[(BiPMo₁₁O₃₉)₄] ⋅ 22 H₂O; (P₄Bi₄Mo₄₄) was characterized by single‐crystal X‐ray diffraction, extended X‐ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix‐assisted laser desorption/ionisation‐time of flight mass spectrometry (MALDI‐TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG‐DSC‐MS). The formation of the nano‐ring in solution was studied by time‐resolved in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L₃ edge indicating a two‐step process consisting of condensation of Mo‐anions and formation of Bi−Mo‐units followed by a rapid self‐assembly to yield the final tetrameric ring structure.

Oligomerization of n-butenes over Ni/SiO2–Al2O3: influence of support modification by steam-treating

The acidic properties of a selected SiO₂–Al₂O₃ support material have been modified by steam-treating to study the influence on the formation of active nickel sites for butene oligomerization.

Effect of Formaldehyde in Selective Catalytic Reduction of NOx by Ammonia (NH3-SCR) on a Commercial V2O5-WO3/TiO2 Catalyst under Model Conditions

The impact of formaldehyde (HCHO, formed in vehicle exhaust gases by incomplete combustion of fuel) on the performance of a commercial V₂O₅-WO₃/TiO₂ catalyst in NH₃-SCR of NO_x under dry conditions has been analyzed in detail by catalytic tests, in situ FTIR and transient studies using temporal analysis of products (TAP). HCHO reacts preferentially with NH₃ to a formamide (HCONH₂) surface intermediate. This deprives NH₃ partly from its desired role as a reducing agent in the SCR and diminishes NO conversion and N₂ selectivity. Between 250 and 400 °C, HCONH₂ decomposes by dehydration (major pathway) and decarbonylation (minor pathway) to liberate toxic HCN and CO, respectively. HCN was proven to be oxidized by lattice oxygen of the catalyst to CO₂ and NO, which enters the NH₃-SCR reaction.

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions

Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)Cu^I‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different Cu^II species, a mononuclear (bpy)(NMI)(CH₃CN)Cu^II‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH₃CN)(bpy)(NMI)Cu^II(μ‐OH)₂⋅Cu^II (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)Cu^II‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible Cu^II leads to slight deactivation at extended reaction times.

Alcohol Synthesis from CO2 , H2 , and Olefins over Alkali-Promoted Au Catalysts-A Catalytic and In situ FTIR Spectroscopic Study

Au/TiO₂ and Au/SiO₂ catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO₂ , H₂ , and C₂ H₄ /C₃ H₆ . 1-Propanol or 1-butanol/isobutanol were obtained in the presence of C₂ H₄ or C₃ H₆ . Higher yields of the corresponding alcohols were obtained over TiO₂ -based catalysts in comparison with their SiO₂ -based counterparts. This is caused by an enhanced ability of the TiO₂ -based catalysts for CO₂ activation, as concluded from in situ fourier-transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO₂ conversion into CO and the hydroformylation reaction. The transformation of Au^δ+ to active Au⁰ sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au⁰ sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C₂ H₄ with the catalyst, suggesting its quick reaction with CO and H₂ after activation on Au⁰ sites to form propanol and propane.

The role of speciation of Ni2+ and its interaction with the support for selectivity and stability in the conversion of ethylene to propene

Highly dispersed Ni²⁺ anchored on Al sites of silica–alumina by grafting presents outstanding selectivity in ethylene conversion to propene.

Structural characterization of vanadium environments in MCM-41 molecular sieve catalysts by solid state 51V NMR

Advanced analysis of ⁵¹V NMR chemical shift and quadrupolar tensor parameters revealed novel insights into the structure of vanadium species in MCM-41-based catalysts.

Heterostructured Copper-Ceria and Iron-Ceria Nanorods: Role of Morphology, Redox, and Acid Properties in Catalytic Diesel Soot Combustion

This work reports the synthesis of heterostructured copper-ceria and iron-ceria nanorods and the role of their morphology, redox, and acid properties in catalytic diesel soot combustion. Microscopy images show the presence of nanocrystalline CuO (9.5 ± 0.5 nm) and Fe₂O₃ (7.3 ± 0.5 nm) particles on the surface of CeO₂ nanorods (diameter is 8.5 ± 2 nm and length within 16-89 nm). In addition to diffraction peaks of CuO and Fe₂O₃ nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu²⁺ and Fe³⁺ ions into the fluorite lattice of CeO₂, hence abundant oxygen vacancies in the Cu/CeO₂ and Fe/CeO₂ nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO₂ rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H₂-temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO₂ rods catalyze the soot oxidation reaction at the lowest temperatures under both tight contact (Cu/CeO₂; T50 = 358 °C, temperature at which 50% soot conversion is achieved, followed by Fe/CeO₂; T50 = 368 °C and CeO₂; T50 = 433 °C) and loose contact conditions (Cu/CeO₂; T50 = 419 °C and Fe/CeO₂; T50 = 435 °C). A possible mechanism based on the synergetic effect of redox and acid properties of Cu/CeO₂ nanorods was proposed: acid sites can activate soot particles to form reactive carbon species, which are oxidized by gaseous oxygen/lattice oxygen activated in the oxygen vacancies (redox sites) of ceria rods.

Synergistic effect of VOx and MnOx surface species for improved performance of V2O5/Ce0.5Ti0.5−xMnxO2−δ catalysts in low-temperature NH3-SCR of NO

Inserting adjacent Mn³⁺/Mn²⁺ and VO³⁺/VO²⁺ redox couples in Ce_1−xTi_xO₂ improves catalytic performance.

Upgrading of bio-oil and subsequent co-processing under FCC conditions for fuel production

NiCo/ZSM-5 revealed a bio-oil HDO deoxygenation degree of 39% and increase of the heating value of product oil to 33.3 MJ kg⁻¹.

Stability studies of ionic liquid [EMIm][NTf2] under short-term thermal exposure

Mass spectrometer coupled TG analysis was used to identify decomposition products of thermally highly stressed ionic liquids.

Nature of surface carbon species and pathways of their formation in the heterogeneously catalysed acetoxylation of toluene

The origins of surface carbon species in the acetoxylation of toluene to benzyl acetate over Pd–Sb/TiO₂ catalyst and their formation pathways were systematically investigated.

Photocatalytic acceptorless alkane dehydrogenation: scope, mechanism, and conquering deactivation with carbon dioxide

Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers.

Highly selective visible light-induced Ti–O bond splitting in an ansa-titanocene dihydroxido complex

Visible light irradiation of an ansa-titanocene(iv) dihydroxido complex Me₄Si₂(C₅Me₄)₂Ti(OH)₂ induces highly selective Ti–O bond activation to exclusively yield Ti(iii) complexes.

An innovative approach for highly selective direct conversion of CO₂ into propanol using C₂H₄ and H₂

Multifunctional catalysts are developed for converting CO2 with C2H4 and H2 into propanol. Au nanoparticles (NP) supported on TiO2 are found to facilitate this reaction. The activity and selectivity strongly depend on NP size, which can be tuned by the method of Au deposition and by promoting with K. The promoter improves the selectivity to propanol. Under optimized reaction conditions (2 MPa, 473 K, and CO2/H2/C2H4=1:1:1), CO2 is continuously converted into propanol with a near-to-100% selectivity. Catalytic tests as well as mechanistic studies by in situ FTIR and temporal analysis of products with isotopic tracers allow the overall reaction scheme to be determined. Propanol is formed through a sequence of reactions starting with reverse water-gas shift to reduce CO2 to CO, which is further consumed in the hydroformylation of ethylene to propanal. The latter is finally hydrogenated to propanol, while propanol hydrogenation to propane is suppressed.

Notizen: Die Kristallstruktur von [(CH3)4N]FeF4 · H2O mit einem di(µ-fluoro)-verbrückten [Fe2F8(H2O)2]2–-Anion / Crystal Structure of [(CH3)4N]FeF4 · H2O with a Di(μ-fluoro)-Bridged [Fe2F8(H2O)2]2- Anion

Single crystals of [(CH3)4N]FeF4·H2O have been prepared from aqueous HF solution. The crystal structure was determined by X-ray diffraction: space group P1̄, Z = 2 (or 1 dimeric unit), a = 705.7(5), b = 818.5(8), c = 915.2(12) pm, α = 65.46(10)°, β = 82.90(9)°, γ = 72.76(7)°, R/wR = 0.047/0.021. The structure consists of centrosymmetrical dimeric anions [Fe2F8(H2O)2]2- with fluorine double bridges and is isotypic with [(CH3)4N]VOF3 · H2O. Intramolecular H-bonds are found between the axial water and fluoride ligands. By additional strong intermolecular H-bonds (O ··· F 258 pm) the anions are connected to form infinite parallel chains between which the TMA cations are located. [(CH3)4N]AlF4 · H2O is shown to be isotypic.