An unusual chemoselective hydrogenation of quinoline compounds using supported gold catalysts.

The pursuit of modern sustainable chemistry has stimulated the development of innovative catalytic processes that enable chemical transformations to be performed under mild and clean conditions with high efficiency. Herein, we report that gold nanoparticles supported on TiO(2) catalyze the chemoselective hydrogenation of functionalized quinolines with H(2) under mild reaction conditions. Our results point toward an unexpected role for quinolines in gold-mediated hydrogenation reactions, namely that of promoter; this is in stark contrast to what prevails in the traditional noble metal Pd-, Pt-, and Ru-based catalyst systems, in which quinolines and their derivatives typically act as poisons. As a result of the remarkable promotional effect of quinoline molecules to H(2) activation over supported gold, the transformation can proceed smoothly under very mild conditions (even at temperatures as low as 25 °C). Of practical significance is that various synthetically useful functional groups including halogens, ketone, and olefin remain intact during the hydrogenation of quinolines. Moreover, the protocol also shows promise for the regiospecific hydrogenation of the heterocyclic ring of a variety of other biologically important heteroaromatic nitrogen compounds, such as isoquinoline, acridine, and 7,8-benzoquinoline, in a facile manner. Apart from its importance in catalytic hydrogenation, we believe that this intriguing self-promoted effect by reactant molecules may have fundamental implications for the broad field of gold catalysis and form the basis for development of new catalytic procedures for other key transformations.

Efficient subnanometric gold-catalyzed hydrogen generation via formic acid decomposition under ambient conditions.

Formic acid (FA) has tremendous potential as a safe and convenient source of hydrogen for sustainable chemical synthesis and renewable energy storage, but controlled and efficient dehydrogenation of FA by a robust solid catalyst under ambient conditions constitutes a major challenge. Here, we report that a previously unappreciated combination of subnanometric gold and an acid-tolerant oxide support facilitates the liberation of CO-free H(2) from FA. Applying an ultradispersed gold catalyst comprising TEM-invisible gold subnanoclusters deposited on zirconia to a FA-amine mixture affords turnover frequencies (TOFs) up to 1590 per hour and a turnover number of more than 118,400 at 50 °C. The reaction was accelerated at higher temperatures, but even at room temperature, a significant H(2) evolution (TOFs up to 252 h(-1) after 20 min) can still be obtained. Preliminary mechanistic studies suggest that the reaction is unimolecular in nature and proceeds via a unique amine-assisted formate decomposition mechanism on Au-ZrO(2) interface.

The conformational transition pathway of ATP binding cassette transporter MsbA revealed by atomistic simulations.

ATP binding cassette transporters are integral membrane proteins that use the energy released from ATP hydrolysis at the two nucleotide binding domains (NBDs) to translocate a wide variety of substrates through a channel at the two transmembrane domains (TMDs) across the cell membranes. MsbA from Gram-negative bacteria is a lipid and multidrug resistance ATP binding cassette exporter that can undergo large scale conformational changes between the outward-facing and the inward-facing conformations revealed by crystal structures in different states. Here, we use targeted molecular dynamics simulation methods to explore the atomic details of the conformational transition from the outward-facing to the inward-facing states of MsbA. The molecular dynamics trajectories revealed a clear spatiotemporal order of the conformational movements. The disruption of the nucleotide binding sites at the NBD dimer interface is the very first event that initiates the following conformational changes, verifying the assumption that the conformational conversion is triggered by ATP hydrolysis. The conserved x-loops of the NBDs were identified to participate in the interaction network that stabilizes the cytoplasmic tetrahelix bundle of the TMDs and play an important role in mediating the cross-talk between the NBD and TMD. The movement of the NBD dimer is transmitted through x-loops to break the tetrahelix bundle, inducing the packing rearrangements of the transmembrane helices at the cytoplasmic side and the periplasmic side sequentially. The packing rearrangement within each periplasmic wing of TMD that results in exposure of the substrate binding sites occurred at the end stage of the trajectory, preventing the wrong timing of the binding site accessibility.

CO oxidation catalyzed by a single gold atom: benchmark calculations and the performance of DFT methods.

Quantum chemical calculations were carried out on CO oxidation catalyzed by a single gold atom. To investigate the performance of density functional theory (DFT) methods, 42 DFT functionals have been evaluated and compared with high-level wavefunction based methods. It was found that in order to obtain accurate results the functionals used must treat long range interaction well. The double-hybrid mPW2PLYP and B2PLYP functionals are the two functionals with best overall performance. CAM-B3LYP, a long range corrected hybrid GGA functional, also performs well. On the other hand, the popular B3LYP, PW91, and PBE functionals do not show good performance and the performance of the latter two are even at the bottom of the 42 functionals. Our accurate results calculated at the CCSD(T)/aug-cc-pVTZ//mPW2PLYP/aug-cc-pVTZ level of theory indicate that Au atom is a good catalysis for CO oxidation. The reaction follows the following mechanism where CO and O(2) adsorb on Au atom forming an Au(OCOO) intermediate and subsequently O(2) transfer one oxygen atom to CO to form CO(2) and AuO. Then AuO reacts with CO to form another CO(2) to complete the catalytic cycle. The overall energy barrier at 0 K for the first CO oxidation step (Au + CO + O(2)→ AuO + CO(2)) is just 4.8 kcal mol(-1), and that for the second CO oxidation step (AuO + CO → Au + CO(2)) is just 1.6 kcal mol(-1).

A hybrid sol­gel synthesis of mesostructured SiC with tunable porosity and its application as a support for propane oxidative dehydrogenation.

Porous silicon carbide (SiC) is of great potential as catalyst support in several industrially important reactions because of its unique thermophysical characteristics. Previously porous SiC was mostly obtained by a simple sol­gel or reactive replica technique which can only produce a material with low or medium surface area (< 50 m2 g(−1)). Here we report a new hybrid sol­gel approach to synthesize mesostructured SiC with high surface area (151­345 m2 g(−1)) and tunable porosity. The synthesis route involves a facile co-condensation of TEOS and alkyloxysilane with different alkyl-chain lengths followed by carbothermal reduction of the as-prepared alkyloxysilane precursors at 1350 °C. The resulting materials were investigated by X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. A mechanism for the tailored synthesis of mesostructured SiC was tentatively proposed. To demonstrate the catalytic application of these materials, vanadia were loaded on the mesostructured SiC supports, and their catalytic performance in oxidative dehydrogenation of propane was evaluated. Vanadia supported on the mesostructured silicon carbide exhibits higher selectivity to propylene than those on conventional supports such as Al2O3 and SiO2 at the same propane conversion levels, mainly owing to its outstanding thermal conductivity which makes contributions to dissipate the heat generated from reaction thus alleviating the hot spots effect and over-oxidation of propylene.

Validation of density functional methods for the calculation of small gold clusters.

The performance of various density functional theory methods on the geometries and energetics of Au(2), Au(3), Au(4), and Au(5) has been systematically evaluated. The results were compared with those from experiments or high-level wave function theory methods. In the present study, spin-orbit (SO) coupling was considered. It was found that SO coupling plays a very important role in the calculation of both the atomization energies and relative stability of the isomers of gold clusters. Functionals including SO coupling effect will overestimate the atomization energies of gold clusters compared with those just including the scalar relativistic (SC) effect. On the other hand, hybrid functionals will underestimate the atomization energies compared with those of the corresponding pure functionals. For the calculation of the relative stability of the different isomers, many functionals not including SO coupling will predict the wrong stability order. In addition, SO correction to the atomization energy of the cluster (ΔE(SO)) has a weak dependence on the choice of functional. A linear relationship was established between ΔE(SO) and the number of Au atoms and Au-Au bonds in the cluster. The relationship indicates that inclusion of SO coupling will favor the isomer with more Au-Au bonds. Among all of the functionals evaluated, the SO TPSSh method has the best overall performance, and SC M06-L also performs well, although it predicts that the two isomers of Au(3) are almost degenerate in energy.

Gold supported on hydroxyapatite as a versatile multifunctional catalyst for the direct tandem synthesis of imines and oximes.

Two birds with one auric stone: The title system acts as a highly efficient heterogeneous catalyst for the one-pot tandem synthesis of imines or oximes from alcohols and the corresponding amines under mild conditions (see scheme; HAP = hydroxyapatite).

Efficient and chemoselective reduction of carbonyl compounds with supported gold catalysts under transfer hydrogenation conditions.

A new heterogeneous catalytic transfer hydrogenation (CTH) system, consisting of a non-flammable supported Au catalyst along with 2-propanol as the hydrogen donor, was proven to be effective for chemoselective reduction of a wide range of aromatic ketones and aldehydes to the corresponding alcohols.

A unique microwave effect on the microstructural modification of Cu/ZnO/Al2O3 catalysts for steam reforming of methanol.

A short time (3-10 min) of microwave irradiation on the CuO/ZnO/Al2O3 oxide precursor can result in a unique tailored microstructural modification on the catalyst, leading to a significantly enhanced performance for H2 production from steam reforming of methanol.

Fabrication of mesoporous core-shell structured titania microspheres with hollow interiors.

Thermally stable mesoporous core-shell structured titania microspheres with well-defined hollow interiors were directly prepared by a novel hydrothermal precipitation of TiCl4 in the presence of urea and ammonium sulfate.

CuCl catalyst heterogenized on diamide immobilized SBA-15 for efficient oxidative carbonylation of methanol to dimethylcarbonate.

CuCl has been successfully immobilized on a novel diamide modified SBA-15, and proven to be an efficient heterogenized catalyst for the oxidative carbonylation of methanol to dimethylcarbonate.

Highly efficient VOx/SBA-15 mesoporous catalysts for oxidative dehydrogenation of propane.

Highly dispersed vanadia species on SBA-15 mesoporous silica have been found to exhibit a highly efficient catalytic performance for the oxidative dehydrogenation (ODH) of propane to light olefins (propene + ethylene).

Efficient and exceptionally selective semireduction of alkynes using a supported gold catalyst under a CO atmosphere.

A new efficient method for chemo- and regio-selective semireduction of alkynes using CO/H2O as the hydrogen source catalyzed by gold supported on high surface area TiO2 was developed. A facile and practical synthesis of 1,2-dideuterioalkenes was also realized by using CO/D2O as the reducing agent.

Propylene from renewable resources: catalytic conversion of glycerol into propylene.

Propylene, one of the most demanded commodity chemicals, is obtained overwhelmingly from fossil resources. In view of the diminishing fossil resources and the ongoing climate change, the identification of new efficient and alternative routes for the large-scale production of propylene from biorenewable resources has become essential. Herein, a new selective route for the synthesis of propylene from bio-derived glycerol is demonstrated. The route consists of the formation of 1-propanol (a versatile bulk chemical) as intermediate through hydrogenolysis of glycerol at a high selectivity. A subsequent dehydration produces propylene.