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The catalytic production of methyl methacrylate through the direct oxidative esterification of methacrolein is important in terms of green chemistry and sustainable development. In the present work, Au nanoparticles supported on three needle-like, lamella-like, and rodlike hydroxyapatites were synthesized. We demonstrated that needle-like hydroxyapatite could facilitate the higher dispersion of Au species because of its high specific surface area, and the strong interaction between the Au nanoparticles and the support resulted in the formation of more surface defects because of the existence of partially encapsulated Au particles by the needle-like hydroxyapatite. The surface defects were related closely to the generation of strong basic sites. Compared with the other two materials, the Au supported on the needle-like hydroxyapatite catalyst, which had a large amount of surface acid-base sites, exhibited a much higher catalytic activity and selectivity to methyl methacrylate in the direct oxidative esterification of methacrolein with methanol under mild reaction conditions (i.e., ambient pressure, low reaction temperature of 70 °C, and low methanol/aldehyde ratio of 8:1). The superior catalytic performance of the Au supported on needle-like hydroxyapatite catalyst was attributable to a cooperative effect between abundant acid-base sites for the preferential chemisorption of methacrolein and highly dispersed active Au species for the favorable formation of β-hydride and oxygen activation. The present findings open a new and promising route for the practical production of methyl methacrylate using high-performance hydroxyapatite-supported metal catalyst systems. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, we report a facile synthetic approach for supported copper nanocatalysts with a thin nitrogen‐doped carbon (CN) overlayer. This Cu@CN catalyst was directly generated by a thermal decomposition of Cu‐Al layered double hydroxide (CuAl‐LDH)/melamine hybrid precursor, and employed in the liquid‐phase transfer dehydrogenation of primary aliphatic alcohols. The strategy was found to be useful for the formation of a very thin in situ formed CN overlayer of 0.5–0.7 nm in thickness on copper nanoparticles of about 8.5 nm in diameter. Compared with uncoated copper‐based catalyst derived from pristine CuAl‐LDH, as‐fabricated Cu@CN catalyst showed significantly enhanced catalytic activity, which was attributed to the surface cooperative effect among strong Lewis base sites originating from the CN layer, well‐dispersed Cu0 nanoparticles and Cu+ species, thereby greatly promoting the activation of hydroxyl group in primary aliphatic alcohols and the following abstraction and transfer of hydrogen. Most importantly, the thin CN overlayer could successfully stabilize copper nanoparticles, thus preventing the leaching and the growth of copper species over the course of the reaction. This work offers a new strategy for fabricating cost‐effective, highly efficient and extremely stable supported copper catalysts for the transfer dehydrogenation of primary aliphatic alcohols. [ABSTRACT FROM AUTHOR]

The efficient gas-phase selective hydrogenation of a series of esters to the corresponding alcohols was achieved over well-dispersed aluminum-doped zirconia-supported copper nanocatalysts (Cu/Al-ZrO2), which were prepared through a homogeneous coprecipitation route in the presence of cetyl trimethyl ammonium bromide. The characterization revealed that the structure and catalytic performance of Cu/Al-ZrO2 nanocatalysts were profoundly affected by the addition of Al. Compared with the Al-free catalyst, Al-doped materials had higher specific surface areas and smaller copper nanoparticles. In particular, the results confirmed that the incorporation of Al into the ZrO2 framework could form tetrahedrally coordinated Al3+ species, leading to the improvement of metal dispersion and the formation of more surface Lewis acid sites. In the gas-phase selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG), 100 % DMO conversion, 97.1 % EG selectivity, and a high turnover frequency of 16.9 h−1 were achieved over Cu/Al-ZrO2 catalyst with a Al/(Cu+Zr+Al) mass ratio of 0.1. The high efficiency of Cu/Al-ZrO2 catalysts in DMO hydrogenation was attributed mainly to the surface synergistic catalytic effect between highly dispersed metallic copper species and strong Lewis acid sites, which promoted the hydrogenation reaction related to the ester groups, unlike the single case of Cu+Cu0 synergy reported previously that was found to control the extent of hydrogenation. The obtained catalysts displayed excellent catalytic performance in the gas-phase hydrogenation of other esters including dimethyl succinate, dimethyl maleate, dimethyl adipate, and 1,4-cycolhexane dicarboxylate. [ABSTRACT FROM AUTHOR]

The uniform Pd nanoparticles were immobilized on the surface of spinel-type ZnAlO support for Suzuki-Miyaura coupling reactions. High-surface-area ZnAlO support with microporous framework was successfully synthesized utilizing concurrent hexamethylenetetramine hydrolysis and homogeneous coprecipitation induced spontaneously under solvothermal conditions. The obtained support Pd catalyst was used as heterogeneous and recyclable catalyst for the Suzuki-Miyaura coupling reaction in an environmentally friendly ethanol solvent under ligand-free ambient conditions, and exhibited excellent catalytic activity. The remarkable catalytic activity is attributed to the homogeneous distribution of small Pd nanoparticles on the ZnAlO matrix as well as the strong metal-support interaction. Furthermore, the catalytic activity did not deteriorate after recycling for five times, suggestive of the good stability of the catalyst. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Supported Pd nanoparticle catalystsover Mg–Al mixed metal oxides derived from layered double hydroxideswere prepared by three different approaches, including coprecipitation,anion-exchange, and impregnation, in order to enhance the metal dispersionand thus facilitate the growth of uniform multiwalled carbon nanotubes(CNTs) via catalytic chemical vapor deposition of methane. The effectsof preparation methods for supported Pd catalysts on the morphologiesand microstructures of CNTs formed were investigated. The resultsrevealed that the characteristics of CNTs were strongly correlatedto the dispersion of active Pd species in the catalysts, and the structuraldefects and the diameter of CNTs were reduced with the increasingmetal dispersion. Especially, the anion-exchange route for preparationof supported Pd catalyst was appropriate for the growth of uniformbamboo-like CNTs with fewer defects, which could be contributed tothe presence of more uniform and smaller Pd0nanoparticleshighly dispersed over Mg–Al mixed-metal oxides. [ABSTRACT FROM AUTHOR]

Abstract: Novel marigold-like carbonate-type Mg–Al layered double hydroxide (MgAl-CO3-LDH) micro-nanostructures with surface curved and intercrossed nanosheets were synthesized successfully via a two-step intercalation route, which involved a primary intercalation of dodecylsulfonate (DS−) anion through urea hydrolysis, followed by exchanging interlayer DS− anions with anions in the presence of a cationic type surfactant (hexadecyl trimethyl ammonium bromide). The possible formation mechanism of such MgAl-CO3-LDH micro-nanostructure was proposed tentatively. Furthermore, the resulting Mg–Al mixed metal oxides obtained by calcining MgAl-CO3-LDH at 500°C still maintain the three-dimensional marigold-like morphology to some extent, indicative of the high thermal stability of micro-nanostructures. The findings in this work may provide a feasible approach for the special morphosynthesis of carbonate-type LDH nanomaterials. [Copyright &y& Elsevier]

Abstract: Ni–Al layered double hydroxides (LDHs) were successfully synthesized through a novel reduction–oxidation route, which involved a rapid reduction of Ni2+ cations and nucleation in a colloid mill, followed by an oxidation of metallic nickel nuclei and structural transformation under hydrothermal conditions in the presence of sodium carbonate. The results indicated that the concentration of sodium carbonate and hydrothermal reaction temperature had important influence on the growth of LDH phase, and NiAl-LDH crystals with high crystallinity and good homogeneity could be achieved under the optimal conditions. The possible formation mechanism of a NiAl-LDH compound was proposed tentatively. The present work provided a new method for a scale-up synthesis of a variety of well-crystallized LDH materials. [Copyright &y& Elsevier]

Aiming at the main challenge of poor atomic economy for selective oxidation of hydrocarbons, synergistic catalysis on heterogenous catalysts has been focused on precisely regulating oxidation of specific chemical bonds in organic substrates. Here, a series of copper nanocatalysts loaded on Mn-substituted SrTiO 3 perovskite-type oxides with varying Mn/Ti ratios for cyclohexylbenzene (CHB) oxidation to form cyclohexylbenzene-1-hydroperoxide (CHBHP) were successfully synthesized by coprecipitation method assisted by a micro-liquid-film reactor. It was found that the introduction of manganese created numerous oxygen vacancies in nanocatalysts, promoting the activation of oxygen molecules. Moreover, both copper and manganese ions enhanced the activated adsorption of CHB substrate. In particular, as-constructed Cu-based nanocatalyst with a substitution of 15% Mn into Ti sites showed superior catalytic oxidation efficiency with a ∼30% yield of CHBHP product, which is at the highest level compared with previously reported heterogenous catalysts, mainly attributable to the favorable synergy between copper, manganese, and oxygen vacancies. This work sheds light on the importance of multi-active site synergistic catalysis in advanced alkane oxidation processes. [Display omitted] • Copper nanocatalysts loaded on Mn-substituted SrTiO 3 perovskites were fabricated. • Mn substitution led to the generation of oxygen vacancies and multivalent Mn ions. • The enhanced cyclohexylbenzene oxidation to hydroperoxide was realized. • High catalytic efficiency was attributable to synergy of oxygen vacancy and Mn-substitution. [ABSTRACT FROM AUTHOR]

• MgO-decorated ZrO 2 nanoparticles were utilized to support Ru0 nanoparticles. • The formation of Mg-O-Zr structures favored the enhanced basicity of MgO-ZrO 2 support. • The enhanced hydrodeoxygenation of guaiacol was achieved by the introduction of MgO. • Ru0 sites together with basic sites contributed to the high efficiency. Presently, it is well-recognized that surface acidic sites on supported metal catalysts play an important role in promoting the hydrodeoxygenation (HDO) of lignin-derived phenolic compounds. In the present work, new insights into the promotion role of surface basic sites on the catalytic performance of MgO-decorated nanostructured ZrO 2 supported Ru nanocatalysts in the HDO of guaiacol were attained. It was found that the adsorption capacity of guaiacol and the HDO ability increased with the density of surface basic sites on as-modified Ru-based catalysts. Combining surface-interface microstructural characterizations of Ru-based catalysts and catalytic testing results with in-situ diffused reflectance infrared Fourier transform spectroscopy of guaiacol adsorption, it was unveiled that surface basic sites induced by the introduction of MgO on the ZrO 2 surface could favor the preferential adsorption of guaiacol through the hydroxyl group interacting with surface basic sites and thus simultaneously the indirect activation of the C ring -OCH 3 bond, thereby boosting the guaiacol HDO to produce cyclohexanol via the demethoxylation and following ring-hydrogenation processes. The present study may provide a promising strategy to design next generation supported metal catalysts with the improved surface basicity for the HDO of lignocellulose-derived phenolic derivates. [Display omitted] [ABSTRACT FROM AUTHOR]

A three-dimensional ordered macroporous Co 3 O 4 (OM-Co 3 O 4) supported Ru catalyst was developed for the efficient hydrodeoxygenation (HDO) of anisole. It is revealed that small-sized Ru nanoparticles evenly distributed over the surface of OM-Co 3 O 4 with large quantities of oxygen vacancies could strongly capture Ru0 species, thereby resulting in strong Ru-Co 3 O 4 interactions. Compared with commercial Co 3 O 4 supported Ru catalyst, Ru/OM-Co 3 O 4 displays a better catalytic HDO performance, with a high cyclohexane yield of 92.4% at 250 °C and 0.5 MPa hydrogen pressure after 5 h on stream. Such a significant efficiency of Ru/OM-Co 3 O 4 is mainly attributed to both high dispersion of Ru0 species and an enhanced formation of surface defects, as well as the unique macroporous framework of OM-Co 3 O 4 support. [Display omitted] • Ordered macroporous Co 3 O 4 supported Ru catalyst was constructed. • Such Ru-based nanocatalyst was highly active for the hydrodeoxygenation of anisole. • Macroporous Co 3 O 4 facilitated the formation of highly dispersed Ru nanoparticles. • Highly dispersion Ru NPs together with surface defects and macroporous framework contributed to high efficiency. [ABSTRACT FROM AUTHOR]

In the work, hybrid nanocomposite of Ni–Al layered double hydroxide (LDH) and carbon nanotubes (LDH/CNTs) was assembled via one-pot hydrothermally assisted coprecipitation approach and applied as the thermal stabilizer in polyvinyl chloride (PVC) resin. Various structural characterizations revealed that smaller LDH nanoplatelets could be uniformly dispersed on the surface of CNTs or closely combined with the CNTs matrix, thus forming unique hybrid nanostructure and strong LDH-CNTs interactions. The thermogravimetry (TGA), Congo red tests, and TG-fourier transform infrared (TG-FTIR) experiments for the PVC-based composites demonstrated that compared with pristine NiAl-LDH and CNTs, as-assembled LDH/CNTs nanocomposite exhibited greatly enhanced thermal stabilization effect on PVC resin. Especially, PVC/LDH/CNTs composite with 5.0 phr of LDH/CNTs additive delivered a superior thermal stabilization effect on PVC to other PVC-based composites, along with the greatly increased maximum degradation temperature and the improved removal efficiency of hydrogen chloride by about 40 °C and 64.8%, respectively. It was concluded that through the assembly of NiAl-LDH with CNTs, the enlarged LDH interlayer spacing, enhanced dispersion of NiAl-LDH component in PVC resin, and strengthened interfacial interaction between NiAl-LDH and PVC could account for the improved thermal stabilization effect of LDH/CNTs additive on PVC during the pyrolysis of PVC. • Hybrid nanocomposite of NiAl-LDH and CNTs was successfully assembled. • Strong interactions between highly dispersive LDH nanosheets and CNTs could form. • As-assembled LDH/CNTs presented excellent thermal stabilization effect on PVC resin. • LDH structure/composition and LDH-PVC interaction affected the stabilization efficiency. [ABSTRACT FROM AUTHOR]