Guoli Fan

Facile synthesis and enhanced catalytic performance of graphene-supported Ni nanocatalyst from a layered double hydroxide-based composite precursor

In this paper, graphene-supported Ni nanocatalyst (Ni/G) was prepared via self-reduction of a hybrid Ni–Al layered double hydroxide/graphene (NiAl-LDH/G) composite precursor. NiAl-LDH/G nanocomposite was assembled via a facile one-step coprecipitation route, which involved the nucleation and growth of NiAl-LDH, simultaneously accompanied by the reduction of graphene oxide without the addition of any reducing agents. The characterization results demonstrated that NiAl-LDH nanoplatelets were homogeneously dispersed on both sides of an exfoliated, structurally flexible graphene The graphene component in the precursor, serving as reducing agent, could in situ reduce Ni2+ species to Ni0 on heating under an inert atmosphere, thus facilitating the formation of highly dispersed Ni nanoparticles with a uniform size. Compared with those prepared by conventional methods, as-formed graphene-supported Ni nanocatalyst exhibited superior catalytic performance in the liquid phase selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde owing to the much higher metal dispersion and smaller size of Ni nanoparticles in the catalyst. The present finding provides a simple approach to fabricate new types of graphene-supported, metal-based heterogeneous catalysts with advanced catalytic performance.

Solvent-free oxidation of ethylbenzene over hierarchical flower-like core–shell structured Co-based mixed metal oxides with significantly enhanced catalytic performance

Herein, we reported the development of new and cost-effective cobalt-based metal oxide catalysts for the oxidation of ethylbenzene, which is considered to be of much importance for the production of high value-added raw materials. The heterogeneous Co-based catalyst system, hierarchical flower-like core–shell structured Co–Zn–Al mixed metal oxides supported on alumina (CoZnAl-MMO/Al2O3), was reproducibly prepared by a two-step process, which involved in situ growth of a two-dimensional Co–Zn–Al layered double hydroxide precursor on amorphous alumina microspheres followed by calcination. The materials were characterized by XRD, SEM, TEM, HRTEM, TPR, XPS and nitrogen adsorption–desorption measurement. The results revealed that CoZnAl-MMO/Al2O3 catalysts exhibited high dispersion of cobalt species due to well-developed three-dimensional flower-like CoZnAl-MMO platelets as well as the separating effect of the resulting ZnO phase. As-synthesized CoZnAl-MMO/Al2O3 catalysts were studied in the oxidation of ethylbenzene without the addition of any solvent and additive using tert-butyl hydroperoxide as the oxygen source and showed much higher catalytic activity and selectivity for acetophenone compared with the conventional supported Co-based catalyst prepared by incipient impregnation. Furthermore, such cost-effective CoZnAl-MMO/Al2O3 catalysts possessed high stability and could be reused at least three times without remarkable loss of the catalytic activity.

Surface synergistic effect in well-dispersed Cu/MgO catalysts for highly efficient vapor-phase hydrogenation of carbonyl compounds

The highly efficient vapor-phase selective hydrogenation of carbonyl compounds (e.g. furfural (FAL) and dimethyl 1,4-cyclohexane dicarboxylate (DMCD)) to corresponding alcohols was achieved excellently over well-dispersed MgO-supported copper catalysts (Cu/MgO), which were prepared by an alternative separate nucleation and aging step method. The characterization results revealed that the structure and catalytic performance of the as-formed Cu/MgO catalysts were profoundly affected by Cu loading. Especially, the results confirmed that the decrease in the Cu loading could lead to the improvement of metal dispersion and the formation of more surface strong Lewis basic sites. In the vapor-phase selective hydrogenation of FAL to furfuryl alcohol (FOL) and DMCD to 1,4-cyclohexane dimethanol (CHDM), two Cu/MgO catalysts with Cu loadings of 27.6 wt% and 70.9 wt% exhibited superior catalytic performance with higher conversions (>97.3%) and selectivities to alcohols (>96.0%) compared to the other supported ones. The high efficiency of the as-formed Cu/MgO catalysts was mainly attributed to the surface synergistic catalytic effect between the catalytically active metallic copper species and the Lewis basic sites, which held the key to the hydrogenation reaction related to the hydrogen dissociation and the activation of the carbonyl groups.

Enhanced visible-light-induced photocatalytic performance of a novel ternary semiconductor coupling system based on hybrid Zn–In mixed metal oxide/g-C3N4 composites

Hybrid composites of Zn–In mixed metal oxides (ZnIn-MMO) and g-C3N4 were synthesized by a facile thermal decomposition of Zn–In layered double hydroxide (ZnIn-LDH) and melamine mixture precursors. The structural and optical properties of the ZnIn-MMO/g-C3N4 composites were characterized by powder X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectra, photoluminescence spectra, electron spin resonance and transient absorption spectra. The results indicated that ZnIn-MMO nanoparticles were well distributed over the surface of the g-C3N4 sheets formed in situ. Compared with pristine ZnIn-MMO, the as-synthesized ZnIn-MMO/g-C3N4 nanohybrids showed stronger absorption in the visible light region. Furthermore, the ZnIn-MMO/g-C3N4 composite with a g-C3N4 amount of 36 wt% exhibited significantly enhanced photodegradation activity for Rhodamine B under visible light irradiation, in comparison with pure g-C3N4 and ZnIn-MMO, which was attributable to the unique heterostructure of the ternary semiconductor coupling system composed of g-C3N4, In2O3 and ZnO in the composites, facilitating efficient transportation and separation of the photogenerated electron–hole pairs and thus the continuous generation of reactive oxygen species. The present finding provides a simple approach for fabricating new types of visible-light-induced g-C3N4-based semiconductor composite photocatalysts for pollutant degradation in advanced oxidation processes.

Aluminum‐Doped Zirconia‐Supported Copper Nanocatalysts: Surface Synergistic Catalytic Effects in the Gas‐Phase Hydrogenation of Esters

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.

The promotional effect of ZnO addition to supported Ni nanocatalysts from layered double hydroxide precursors on selective hydrogenation of citral

A series of highly-dispersed, ZnO-modified supported nickel nanocatalysts (Ni–ZnO/C) were prepared via in situ self-reduction of hybrid Ni–Zn–Al layered double hydroxide/carbon (NiZnAl–LDH/C) nanocomposite precursors. The materials were characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), scanning transmission electron microscopy (STEM), ammonia temperature-programmed desorption (NH3-TPD), and X-ray photoelectron spectroscopy (XPS). The effect of ZnO addition on the catalytic properties of as-synthesized Ni–ZnO/C catalysts for liquid phase selective hydrogenation of citral to citronellol was examined. It was found that ZnO addition significantly modified their catalytic hydrogenation properties for citral, inducing an improved selectivity toward citronellol. A maximum yield of citronellol (~92%) was achieved when the bulk Zn/Ni atomic ratio was 0.25 in the catalysts. This promotional effect was mainly related to the existence of a ZnO–metal interaction, which was proposed to be responsible for enhanced adsorption of the CO bond in the citral molecule on the surface of catalysts and thus for activation of the CO bond.

Promotional Role of Surface Defects on Carbon‐Supported Ruthenium‐Based Catalysts in the Transfer Hydrogenation of Furfural

The synthesis of highly efficient supported metal catalysts is of vital importance for the modern development of the production of chemicals. In this regard, biomass‐based chemical transformation holds potential promise through many heterogeneous catalytic processes. Herein, we report surface defect engineering on a carbon‐supported, Ru‐based catalyst by a two‐step hybridization–self‐reduction route, which involves the assembly of a hybrid composite of ternary Co‐Al‐Ru layered double hydroxide (CoAlRu‐LDH) and amorphous carbon through the carbonization of glucose and a subsequent in situ self‐reduction process. The results revealed that Ru3+ species in the resulting CoAlRu‐LDH‐C composite could be reduced in situ to Ru0 species by the carbon component in the hybrid composite, and Co‐containing spinels with a large quantity of surface oxygen vacancies could be formed simultaneously on the surface. The as‐fabricated Ru‐based catalyst showed a superior catalytic performance in the liquid‐phase transfer hydrogenation of furfural to furfuryl alcohol using benzyl alcohol as hydrogen donator to other Ru‐based catalysts derived from LDH‐C composite precursors. It was proven that surface defects (i.e., oxygen vacancies, Co2+ species) could enable the chemisorption of furfural spatially and ensure the activation of its carbonyl groups, which promoted the transfer hydrogenation greatly.

A gas-phase coupling process for simultaneous production of γ-butyrolactone and furfuryl alcohol without external hydrogen over bifunctional base-metal heterogeneous catalysts

A solvent-free gas-phase coupling process through hydrogen transfer without external hydrogen supply over novel bifunctional base-metal heterogeneous catalysts was developed for the simultaneous production of γ-butyrolactone and furfuryl alcohol with high yields of 95.0% from biomass-derived compounds. Such a practical, unparallely efficient and environmentally benign process makes it promising in terms of both green sustainable chemistry and industrial perspective.

Synthesis of highly dispersed boron-promoted nickel nanocatalysts and significantly enhanced catalytic performance in hydrodechlorination of chlorobenzene

Control of the dispersion and size of metallic nanoparticles, as well as metal–support interaction, is of vital importance to enhance the catalytic performance of supported metal nanocatalysts. In this work, carbon-supported boron-promoted Ni nanocatalysts (B–Ni) were synthesized via an in situ self-reduction process of hybrid borate-intercalated NiAl-layered double hydroxide/carbon nanocomposites, and the promotional effect of boron on the catalytic performance of Ni nanocatalysts formed in liquid phase hydrodechlorination of chlorobenzene was studied. A series of XRD, TEM, STEM, XPS, low temperature N2 adsorption, and H2 chemisorption results revealed that the resulting spherical B-modified Ni nanoparticles were homogeneously dispersed and anchored tightly on the surface of the carbon support. A suitable amount of boron was essential for the formation of highly dispersed and uniform nanoparticles and pronounced surface Ni–B interaction, as well as strong Ni–B–support interactions, accounting for the significantly enhanced hydrodechlorination activity, in comparison with a B-free Ni catalyst. Moreover, as-synthesized B–Ni nanocatalysts exhibited good stability, without obvious aggregation and loss of active species after five recycles.

Highly Efficient Hybrid Cobalt–Copper–Aluminum Layered Double Hydroxide/Graphene Nanocomposites as Catalysts for the Oxidation of Alkylaromatics

The selective oxidation of alkylaromatics is of vital importance for the production of high‐added‐value raw materials. The development of highly efficient heterogeneous catalytic oxidation systems under mild conditions has become an attractive research area. In this work, hybrid Co–Cu–Al layered double hydroxide/graphene (CoCuAl‐LDH/graphene) nanocomposites, which were assembled successfully by a one‐step coprecipitation route without the use of any additional reducing agents, were used as highly efficient catalysts for the liquid‐phase selective oxidation of ethylbenzene using tert‐butyl hydroperoxide as the oxidant. A series of characterizations revealed that graphene could stabilize CoCuAl‐LDH nanoplatelets effectively in the nanocomposites, and in turn, highly dispersed CoCuAl‐LDH could prevent the aggregation of the graphene nanosheets. By fine‐tuning the mass ratio of graphene to CoCuAl‐LDH, such nanocomposites offered a tunable catalytic oxidation performance. In particular, the nanocomposite with the graphene/CoCuAl‐LDH mass ratio of 0.4:1 exhibited a remarkable catalytic performance with a considerable conversion (96.8 %) and selectivity to acetophenone (>95.0 %), which was mainly attributed to the synergism between the active CoCuAl‐LDH component and the graphene matrix in the unique hetero‐nanostructure. Moreover, the as‐assembled nanocomposite catalysts displayed good recyclability and were active for the selective oxidation of other alkylaromatics.