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In the present work, a La-doped Mg–Al mixed metal oxide supported copper catalyst (Cu/La–MgAlO) was synthesized through a layered double hydroxide precursor route. The materials were characterized by powder X-ray diffraction, transmission electron microscopy, CO2-temperature programmed desorption, Fourier transform infrared spectra of CO2 absorption, and X-ray photoelectron spectroscopy. The results revealed that the introduction of a trace amount of La could significantly improve the surface basicity of the Cu/La–MgAlO catalyst, especially strong Lewis basicity. Compared with the undoped supported Cu catalyst, Cu/La–MgAlO exhibited much higher activity and selectivity in the liquid-phase transfer dehydrogenation of 1-decanol with a 1-decanal yield up to 89%. The excellent catalytic efficiency was mainly ascribed to the surface cooperation between the Lewis basic sites and the adjacent Cu0/Cu+ species. That is, basic sites, especially strong-strength basic sites, held the key to the abstraction of protons from the hydroxyl group in 1-decanol, while the adjacent Cu0 and Cu+ species were responsible for the hydrogen transfer and the adsorption of styrene in the transfer dehydrogenation and hydrogenation reactions, respectively. This study provides a new method for designing cost-effective supported copper-based catalysts highly efficient for the transfer dehydrogenation of primary aliphatic alcohols by modifying the surface basicity of metal oxide supports. [ABSTRACT FROM AUTHOR]

Highly dispersed and stable supported copper-based catalysts for gas-phase hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate (DMCD) to 1,4-cyclohexane dimethanol (CHDM) were synthesized from a single-source Cu–Zn–Al layered double hydroxide (LDH) precursor. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H 2 -TPR), X-ray photoelectron spectroscopy (XPS), N 2 sorption, H 2 -N 2 O titration and transmission electron microscopy (TEM) techniques. The results revealed that calcination temperature for LDH precursors significantly affected the composition, structure, chemical states, and catalytic performance of copper-based catalysts. In the gas-phase selective hydrogenation of DMCD, a high CHDM yield of 95.6% was achieved over copper-based catalyst obtained at calcination temperature of 600 °C. Compared with the conventional Cu/ZnO/Al 2 O 3 and Cr 2 O 3 promoted copper-based catalysts, LDH-derived Cu-based catalysts exhibited higher catalytic performance, which was mainly attributed to the presence of highly dispersed and stable active metallic copper species, as well as a reasonable amount of Cu + species facilitating the activation of ester groups of reactants. [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 gas-phase hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate to 1,4-cyclohexane dimethanol was performed on a well-dispersed Cr-free supported copper-based catalyst derived from a Cu–Mg–Al layered double hydroxide precursor, and achieved a lasting 100% conversion with 99.8% selectivity up to 200 hours. The unprecedented catalytic performance is ascribed to the synergistic effect between surface active Cu0 sites and Lewis base sites. [ABSTRACT FROM AUTHOR]

The highly-dispersed copper-based catalysts for the gas-phase hydrogenation of dimethyl oxalate to ethylene glycol (EG) were prepared from a Cu-Zn-Al layered double hydroxide (LDH) precursor. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N adsorption-desorption, H temperature programmed reduction (H-TPR) and H-NO titration indicated that the composition, texture, and structure of resulting copper-based catalysts were profoundly affected by the calcination temperature of LDH precursor. Moreover, the as-synthesized catalyst calcined at 600 °C was found to exhibit a superior catalytic hydrogenation performance with an EG yield of 94.7 % to the other catalysts calcined at 500 and 700 °C, which should be mainly attributed to the presence of the highly-dispersed active metallic copper species over metal oxide matrix. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

• Indium-doped ZrO 2 supported copper catalysts were in situ constructed. • As-constructed Cu-based catalysts was highly active for the CO 2 hydrogenation. • In situ introduction of indium could tune effectively surface-interface structures. • Surface basicity together with interfacial defects/Cu+ sites contributed to high efficiency. Currently, highly efficient catalytic CO 2 hydrogenation to produce methanol is attracting intensive attention. However, constructing high-performance catalysts for methanol synthesis that can be operated under mild reaction conditions is a challenging task. In this work, a series of indium-doped ZrO 2 supported copper-based catalysts for CO 2 hydrogenation were constructed via one-pot hydrogen bubble-assisted approach. It was manifested that the in situ introduction of indium facilitated the generation of interfacial defects in the form of Zr-Vo-In3+ structure (V o : oxygen vacancy) and interfacial Cu+ sites, as well as surface basic sites originating from In-O pairs, and the catalytic performance of as-constructed In-doped Cu/ZrO 2 catalysts could be efficiently promoted by tuning the indium content. Specifically, the Cu-based catalyst bearing the indium content of 4.0 wt% afforded the quite high space-time yield of methanol (0.398 g MeOH h−1·g cat −1) at 270 °C, while the one with the indium content of 8.0 wt% yielded an increased methanol selectivity by 1.8 times at 250 °C, compared with undoped one. Combining the structural characterizations with catalytic results, it was found that surface medium-strength and strong basic sites together with the contribution from interfacial defective oxygen vacancies and Cu+ sites played key promotional roles on the synthesis of methanol. This finding enables us to design new high-performance Cu-based catalysts for CO 2 hydrogenation by finely turning their surface-interface structures. [ABSTRACT FROM AUTHOR]

Upgrading biomass-derived ethanol to higher alcohols is a significantly promising process involving multi-step tandem reactions finely regulated by multiple active sites. However, the role of multiple active sites in addressing activity and selectivity toward alcohols still remains unclear. Herein, we developed supported copper catalysts decorated with surface trace-level nitrogen-doped carbon (NC) derived from melamine/Cu-Mg-Al layered double hydroxide composite precursors and studied their catalytic performance for converting ethanol to higher alcohols. As-constructed NC-decorated Cu-based catalyst, which was obtained by calcination of the precursor with a melamine/Cu molar ratio of 2:1 at 550 °C, achieved an 82% selectivity to higher alcohols at 63% ethanol conversion under reaction conditions (250 °C, 2 MPa pressure), along with unprecedentedly high ethanol conversion rate of 38.9 mmol·g cat −1·h−1 and production rate of higher alcohols (31.9 mmol·g cat −1·h−1), which are the highest standard among previously reported catalysts to date. By performing comprehensive structural characterizations and density functional theory calculations, it was revealed that surface modification of NC component promoted the dispersion of Cu particles and modulated the electronic structures of Cu species, facilitating the formation of Cu+ sites at metal-support interfaces and surface oxygen vacancies. Moreover, the significantly enhanced catalytic efficiency of Cu catalysts was mainly attributed to the favorable cooperative catalysis of multiple surface-interface active sites (Cu0, Cu+, oxygen vacancies, and acid-base sites), thereby accelerating tandem processes to produce higher alcohols during ethanol conversion. The present findings afford a new strategy for the rational design of high-performance supported copper catalysts for biomass-derived ethanol coupling to higher alcohols. [Display omitted] • Trace-level NC-decorated copper-based catalysts were successfully constructed. • Surface NC modification facilitated the formation of interfacial Cu+ sites and surface oxygen vacancies. • Such catalyst showed excellent performance for upgrading ethanol to higher alcohols. • Favorable cooperation of multiple surface-interface active sites contributed to unprecedentedly high productivity of higher alcohols. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A robust and sustainable NC-decorated copper-based catalyst was developed. • Strong interactions between Cu species and the support were formed. • Highly efficient catalytic transfer hydrogenolysis of HMF was achieved. • Surface cooperation between basic sites and Cu0/Cu+ species was confirmed. Abstract Currently, highly efficient transformation of abundant and low-cost renewable raw biomass into high-quality biofuels and important chemicals is one of the most promising solutions to the current energy crisis, rapid consumption of fossil resources, increasing emission of greenhouse gases and serious environmental pollution. Here, convertible production of promising 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF) biofuels was achieved successfully via green catalytic transfer hydrogenolysis of biomass-derived 5-hydroxymethylfurfural (HMF) using a nitrogen-doped carbon (NC)-decorated copper-based catalyst with cyclohexanol as hydrogen source. DMF or DMTHF with high yield of 96.1% or 94.6% was produced convertibly through simply modulating reaction time. Extensive characterizations revealed that appropriate surface base sites on the catalyst could efficiently promote the activation of alcohol hydroxyl in cyclohexanol and the subsequent release of active hydrogen species, while highly dispersed surface Cu0 nanoparticles and electrophilic Cu+ species were beneficial to the hydrogen transfer and the activation of both the carbonyl group and the hydroxyl group in HMF, respectively. Moreover, as-fabricated NC-decorated Cu-based catalyst presented high stability without obvious loss of catalytic performance after five consecutive cycles, due to the strong interaction between the support and active metal species. Such non-noble metal catalyst has a promising industrial application in the production of valuable biomass fuels. [ABSTRACT FROM AUTHOR]

New Mn-containing spinel-supported copper nanocatalysts were directly generated via a Cu–Mn–Al layered double hydroxide precursor route and employed in gas-phase hydrogenation of dimethyl succinate (DMS) to γ-butyrolactone (GBL). It was found that the introduction of manganese into catalyst precursors led to the formation of Mn-containing spinel phases, thereby giving rise to highly dispersive Cu 0 nanoparticles and a large number of surface defects (i.e., oxygen vacancies (O v ), Mn 2+ species) in reduced catalysts. As-formed copper-based nanocatalysts exhibited exceptional catalytic hydrogenation performance with stability enduring up to 100 h. Such high catalytic efficiency could reasonably be attributed to the surface synergism between Mn 2+ –O v –Mn 2+ defect structures and active metallic copper species, which controlled the key to hydrogenation related to the adsorption of DMS molecules and following activation of carbonyl groups and the dissociation of hydrogen. Most importantly, such copper-based nanocatalysts displayed great potential applications in the hydrogenations of other biomass-derived compounds containing carbonyl groups (e.g., acetol, levulinic acid, levulinic acid esters, and furfural). The present strategy enables us to tune the surface structures of catalysts for designing new type of copper-based catalysts with significantly enhanced catalytic performance. [ABSTRACT FROM AUTHOR]