Single-Step Hydrogenolysis of Furfural to 1,2-Pentanediol Using a Bifunctional Rh/OMS-2 Catalyst.
ABSTRACT: Hydrogenolysis of biomass-derived furfural (FFA) to 1,2-pentanediol (1,2-PeD) was investigated using a bifunctional catalyst with basic and metallic sites, which was synthesized by the hydrothermal method. The synthesized catalyst consisting of rhodium (Rh) supported on an octahedral molecular sieve (OMS-2) of different loadings, such as 0.5, 1, and 1.5% w/w, was studied, and 1% (w/w) loading gave the best results. This 1% w/w Rh/OMS-2 catalyst showed excellent catalytic activity and selectivity for the hydrogenolysis reaction because of better dispersion of rhodium, later revealed by characterization. Furthermore, 1% Rh/OMS-2 catalyst was well characterized in virgin and reused states using various techniques such as Fourier-transform infrared spectroscopy, NH3-temperature-programmed desorption (TPD), CO2-TPD, temperature-programmed reduction, H2 pulse chemisorption, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area, X-ray photoelectron spectroscopy, Raman spectroscopy, and differential scanning calorimetry-thermogravimetry analysis. The catalyst showed a higher surface area of 72 m2/g and the average size of the highly dispersed Rh metal of ?2 nm. The studies were performed in a batch reactor; the catalyst offered almost 100% conversion of FFA with 87% selectivity to 1,2-PeD at 160 °C and 30 atm hydrogen pressure in 8 h. The reaction mechanism and kinetic model have been developed using a dual-site Langmuir-Hinshelwood-Hougen-Watson mechanism. The activation energies were 12.3 and 27.6 kcal/mol, correspondingly. The catalyst was found to be active, selective, and reusable.
Project description:The effects of the addition of ceria and zirconia on the structural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/?-Al2O3) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposition of ceria on ?-Al2O3 from Ce(acac)3, and the rhodium metal is subsequently added, whereas method II is based on a controlled surface reaction technique, that is, the decomposition of metal-organic M(acac)x (in which M=Ce, x=3 and M=Zr, x=4) on Rh/?-Al2O3. The structures of the prepared catalyst materials are characterized ex situ by using N2 physisorption, transmission electron microscopy, high-angle annular dark-field scanning transmission election microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room temperature. By using ceriated and zirconiated precursors, a larger rhodium-based metallic core fraction is obtained in comparison to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and reduction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows significant Rh-Cl interactions for Rh/Al2O3 and Rh/CeOx /Al2O3 (method I) catalysts. After reaction with H2/He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis affords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30-110 atoms), with the incorporation of zirconium providing the largest particle sizes.
Project description:In this work, Cu nanoparticles (Cu NPs, 2-20 nm) supported on Hydrotalcite catalysts exhibit enhanced selectivity for ?-valerolactone (GVL) during hydrogenolysis of levulinic acid (LA). At 260 °C, over 3 wt% Cu achieved 87.5% of LA conversion with a maximum GVL selectivity (95%). In contrast, LA hydrogenolysis over 3Cu/Hydrotalcite catalyst is highly active and stable toward the production of GVL due to balanced acido-basicity and higher Cu dispersion with ultrasmall particle sizes, which are investigated through the temperature programmed desorption (TPD) of ammonia, N2O titration, and transmission electron microscopy (TEM) analysis. Hydrotalcite in combination with inexpensive Cu catalyst is found to be an efficient and environmentally benign for LA hydrogenolysis.
Project description:Rhodium(II)-catalyzed reactions of vinyldiazoacetates with dihydronaphthalenes were systematically studied. These substrates underwent cyclopropanantion and/or the combined C-H activation/Cope rearrangement in good overall yield and with good diastereo- and enantiocontrol. The selectivity of these reactions was profoundly influenced by the nature of the chiral catalyst, the vinyldiazoacetate, and the dihydronaphthalene. The best combinations for achieving the highest selectivity in the cyclopropanation and the combined C-H activation/Cope rearrangement of 1,2-dihydronaphthalenes are methyl 2-diazopent-3-enoate (2a)/Rh(2)(S-DOSP)(4) and methyl 3-(tert-butyldimethylsilyloxy)-2-diazopent-3-enoate (2b)/Rh(2)(S-PTAD)(4). These combinations are very effective at enantiodivergent reactions of 1-methyl-1,2-dihydronaphthalenes.
Project description:Our contribution demonstrates that rhodium, an element that has barely been reported as an active metal for selective dehydrogenation of alkanes becomes a very active, selective, and robust dehydrogenation catalyst when exposed to propane in the form of single atoms at the interface of a solid-supported, highly dynamic liquid Ga-Rh mixture. We demonstrate that the transition to a fully liquid supported alloy droplet at Ga/Rh ratios above 80, results in a drastic increase in catalyst activity with high propylene selectivity. The combining results from catalytic studies, X-ray photoelectron spectroscopy, IR-spectroscopy under reaction conditions, microscopy, and density-functional theory calculations, we obtained a comprehensive microscopy picture of the working principle of the Ga-Rh supported catalytically active liquid metal solution.
Project description:The synthesis and characterization of five-coordinate rhodium(III) and iridium(III) 2,2'-biphenyl complexes [M(CNC-12)(biph)][BArF 4] (M = Rh (1a), Ir (1b)), featuring the macrocyclic lutidine- and NHC-based pincer ligand CNC-12 are reported. In the solid state these complexes are notable for the adoption of weak ?-agostic interactions that are characterized by M···H-C contacts of ca. 3.0 Å by X-ray crystallography and ?(CH) bands of reduced wavenumber by ATR IR spectroscopy. Remarkably, these interactions persist on dissolution and were observed at room temperature using NMR spectroscopy (CD2Cl2) and solution-phase IR spectroscopy (CCl4). The associated metrics point toward a stronger M···H-C interaction in the iridium congener, and this conclusion is borne out on interrogation of 1 in silico using DFT-based NBO and QTAIM analyses. Reaction of 1 with dihydrogen resulted in hydrogenolysis of the biaryl and formation of fluxional hydride complexes, whose ground state formulations as [Rh(CNC-12)H2][BArF 4] (2a?) and [Ir(CNC-12)H2(H2)][BArF 4] (2b?) are proposed on the basis of inversion recovery and variable-temperature NMR experiments, alongside a computational analysis. Reactions of 1 and 2 with carbon monoxide help support their respective structural properties.
Project description:The [Rh(L-alaninate)(cod)] (cod = 1,5-Cyclooctadiene) complex was synthesized and characterized. Asymmetric polymerizations of achiral phenylacetylene with two hydroxyl groups and a dodecyl group (DoDHPA) were performed by using the rhodium complex as the catalyst to provide polymers with a higher molecular weight (>10⁵) than the polymers obtained using the [Rh(cod)Cl]₂ initiator systems. The resulting polymers showed circular dichroism (CD) signals at approximately 310 and 470 nm, indicating that they have a preferential one-handed helical structure. The helix sense in the polymer main chain was controlled by the sign of the catalyst chirality. These findings suggest that the rhodium complex with a chiral amine is the true active species for the helix-sense-selective polymerization of DoDHPA. The [Rh(L-alaninate)(cod)] complex also exhibits high catalytic activity in the polymerization of phenylacetylene (PA) to give a high yield and molecular weight. All these results demonstrate that this Rh complex is an excellent catalyst for the polymerization of phenylacetylene monomers.
Project description:Ruthenium (Ru) supported on activated carbon (AC) and carbon nanotubes (CNTs) was carried out in the hydrogenolysis of sorbitol to ethylene glycol (EG) and 1,2-propanediol (1,2-PD) under the promotion of tungsten (WOx) species and different bases. Their catalytic activities and glycols selectivities strongly depended on the support properties and location of Ru on CNTs, owning to the altered metal-support interactions and electronic state of ruthenium. Ru located outside of the tubes showed excellent catalytic performance than those encapsulated inside the nanotubes. Additionally, the introduction of WOx into Ru/CNTs significantly improved the hydrogenolysis activities, and a complete conversion of sorbitol with up to 60.2% 1,2-PD and EG yields was obtained on RuWOx/CNTs catalyst upon addition of Ca(OH)2. Stability study showed that this catalyst was highly stable against leaching and poisoning and could be recycled several times.
Project description:Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ?2.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400?°C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O2.
Project description:Catalytic, low temperature preferential oxidation (PROX) of carbon monoxide by aqueous [5,10,15,20-tetrakis(4-sulfonatophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (1[Rh(III)]) and [5,10,15,20-tetrakis(3-sulfonato-2,6-difluorophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (2[Rh(III)]) is reported. The PROX reaction occurs at ambient temperature in buffered (4 ? pH ? 13) aqueous solutions. Fluorination on the porphyrin periphery is shown to increase the CO PROX reaction rate, shift the metal centered redox potentials, and acidify ligated water molecules. Most importantly, ?-fluorination increases the acidity of the rhodium hydride complex (pK(a) = 2.2 ± 0.2 for 2[Rh-D]); the dramatically increased acidity of the Rh(III) hydride complex precludes proton reduction and hydrogen activation near neutral pH, thereby permitting oxidation of CO to be unaffected by the presence of H(2). This new fluorinated water-soluble rhodium porphyrin-based homogenous catalyst system permits preferential oxidation of carbon monoxide in hydrogen gas streams at 308 °K using dioxygen or a sacrificial electron acceptor (indigo carmine) as the terminal oxidant.
Project description:The effects of ceria and zirconia on the structure-function properties of supported rhodium catalysts (1.6 and 4 wt?% Rh/?-Al2O3) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on ?-Al2O3 from [Ce(acac)3] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)x] (M=Ce, x=3; M=Zr, x=4) on Rh/?-Al2O3. The structure-function correlations of ceria and/or zirconia-doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier-transform spectroscopy/energy-dispersive extended X-ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time-resolved, in situ conditions. CeOx and ZrO2 facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/?-Al2O3 samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.