The synthesis of new biomass-derived ethers is of great interest for the development of biofuels and biofuel additives. In this study, we report the facile synthesis of a novel bioether ethyl-4-ethoxy pentanoate (EEP) from γ-valerolactone (GVL), a well-known biomass platform compound. The formation of EEP involves the etherification of ethyl-4-hydroxyl pentanoate (EHP) formed by GVL ring opening catalyzed by H-β-zeolite in ethanol. When operated at 140 °C for 2 h under autogenous pressure, the highest EEP yield of 55% was achieved at 62% GVL conversion and 89% EEP selectivity. The EEP yield was significantly improved to 86% by increasing the reaction temperature to 160 °C, where the EEP selectivity reached ∼97%. The extraordinarily high selectivity to EEP over H-β is likely correlated to its unique structure, which has strong Lewis acid sites as well as an optimal pore size.Keywords: acid catalysis; bioether; etherification; pore size effect; β-zeolite;

The clean synthesis of furfural oxime (FO) has been realized through titanosilicate-catalyzed liquid-phase ammoximation of furfural with ammonia and hydrogen peroxide. A detailed investigation of furfural ammoximation over three representative titanosilicates Ti-MOR, TS-1 and Ti-MWW reveals that the reaction involves the hydroxylamine route and the imine route. The hydroxylamine route accounts for the formation of the target product (FO), while the imine route leads to the formation of undesired products such as 2-furylamide and 2-furoic acid. With a high efficiency for hydroxylamine formation, Ti-MOR proves to be superior to TS-1 and Ti-MWW. The catalytic performance of Ti-MOR depends greatly on the operating conditions of the reaction, which is closely related to its activity in catalyzing hydroxylamine decomposition. The decomposition of hydroxylamine and the non-catalytic oxidation of furfural can be effectively suppressed in Ti-MOR-catalyzed ammoximation when employing water as the solvent and adding H2O2 dropwise into the reaction system. Under optimized conditions, Ti-MOR is capable of providing furfural conversion and oxime selectivity both above 97%.

A novel bifunctional ZSM-5@(Co/SiO2) material with a hierarchical core/shell structure was successfully prepared through a simple chemoselective interaction between the crystal surface silica species of zeolite and the external Co2+ source in basic media, which served as an excellent catalyst in the synthesis of green fuels from biomass-derived ethyl esters.

•Ni or NiO in bimetal PdNi catalysts maintains their oxidation state under mild hydrogenation conditions.•Bimetal PdNi catalyst deactivates in the hydrogenation of α-AL and the deactivation rate depends on the oxidation state of Ni, particle size of NiO or Ni, as well as the solvent used.•The deactivation is linked to the dissociated adsorption of α-AL, which mainly takes place on reduced Ni predominating surfaces.We have previously reported the superior catalytic activity of Pd-NiO/SiO2 to Pd-Ni/SiO2 in hydrogenation of α-angelica lactone (α-AL) to gamma-valerolactone (GVL) in a batch reactor. To gain deeper insight into the structure-activity relationship of Pd-Ni bimetal catalyst, a series of NiO/SiO2 with different NiO particle sizes (about 3, 9, and 20 nm in average) were prepared by impregnation method in the presence or absence of ethylene glycol. These materials were used as the support of Pd catalysts for the liquid-phase hydrogenation of α-AL in a fixed bed reactor. The corresponding reduced catalysts, namely Pd-Ni(3, 9, 20)/SiO2 with different Ni particle sizes were obtained by in situ reduction before reaction and then their catalytic activities were investigated. By comparing the catalytic performances of Pd-NiO/SiO2 and Pd-Ni/SiO2 in water or tetrahydrofuran (THF), the effects of oxidation state and particle size of nickel species on the hydrogenation of α-AL in terms of activity and stability were systematically studied. The bimetal catalysts were characterized by BET, XRD, TEM and in situ XAS. The catalytic tests suggested that there was no clear correlation between the initial activity and the particle size of NiO or Ni species, whereas the catalyst durability was particle size dependent and solvent dependent as well. The deactivation mechanism is likely associated with a strong adsorption of organic species on the catalyst surface according to FTIR study on the adsorption behavior of α-AL and GVL on various materials, as well as the C1s XPS spectra of the spent catalysts. The beneficial effect of water in hydrogenation is thereby explained by the less coke tendency due to the relative stronger interaction between water and catalyst surface than that between THF and surface.Download high-res image (66KB)Download full-size image

The hydrogenation of α-angelica lactone (α-AL) was achieved under mild conditions on silica supported Pd–NiO catalysts. NiO and palladium were sequentially loaded on silica by wet-impregnation and deposition–reduction, respectively. First a series of NiO/SiO2 supports with varying Ni contents were prepared by a wet-impregnation method with Ni(NO3)2 as the precursor followed by calcination in air. Then a minute amount of palladium (0.2 wt%) was loaded by a deposition–reduction method using NaBH4 as a reducing reagent. The Pd–NiO catalysts were characterized by nitrogen adsorption, XRD, H2-TPR, XPS and TEM. The NiO were heterogeneously dispersed on silica with particle sizes ranging from 10 to 50 nm, whereas Pd was finely loaded with a diameter less than 5 nm. Nanoscale intimacy between Pd and NiO was noticed by HRTEM, resulting in high catalytic activity in liquid phase hydrogenation of α-angelica lactone to γ-valero lactone (GVL) under mild conditions. 0.2Pd–9.9NiO/SiO2 showed the best activity among all the catalysts investigated, with 82% conversion and 100% selectivity to GVL within several minutes at 30 °C and 0.3–1 MPa H2 pressure.

A binary SiO2/Al2O3 composite with fibrous γ-alumina coating on the external surface of SBA-15 has been synthesized by simply mixing SBA-15 with fibrous boehmite sol, followed by aging and calcination. The textural and acidic properties of the resultant material were characterized by various techniques, i.e. powder X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) spectroscopy, N2 adsorption/desorption, nuclear magnetic resonance (NMR) spectroscopy, and temperature programmed desorption of ammonia and ethanol (NH3-TPD and EtOH-TPD). Coating fibrous γ-alumina stabilized the SBA-15 structure against collapse under critical steaming conditions (800 °C and 4 h) allowing for the facile synthesis of mesoporous aluminosilicate. The migration of aluminum and silicon between the alumina and SBA-15 zones led to the formation of Al–OH–Si with weak acidity which served as the active sites with excellent catalytic performance in the cracking of 1,3,5-triisopropyl benzene (TIPB).

Gamma-valerolactone (GVL), as sustainable feedstock for high-value chemicals and fuel, has been produced by hydrogenation of levulinic acid (LA) or ethyl levulinate (EL). In this work, Pd nanoparticles supported on Nb2O5-doped activated carbon (AC) were prepared via wet incipient impregnation with PdCl2 followed by reduction with NaBH4. The dispersed niobia plays a bifunctional role in the catalytic process: stabilizing Pd nanoparticles and acting as an acidic co-catalyst. This synergistic effect between niobia and Pd leads to an unprecedented high activity of supported Pd catalysts in EL hydrogenation. The synergy is correlated with both the niobia loading and calcination temperature, with 10 wt% Nb2O5 calcined at 500 °C showing the best performance (EL conversion of 87% and GVL selectivity of 97%) under mild reaction conditions (100 °C and 0.5 MPa H2).

The hydrogenation activity of 3 wt.% Pd nanoparticles supported on various mono-group (H, OCH3, NH2, Cl, and NO2) substituted Al–MIL-53 materials has been investigated. Substituents enhanced the dispersion of palladium nanoparticles on Al–MIL-53, leading to a narrow particle size distribution in the range of 2 to 4 nm. Pd nanoparticles on fresh catalysts were present as a mixture of Pd(II) and Pd(0) with different ratios. These Pd species readily became metallic in a hydrogen flow even at room temperature. Their activities in hydrogenation of phenol and phenylacetylene are linked to the substituents on the aromatic ring of the framework. Catalysts with electron-donating groups (OCH3 and NH2) show much higher activity than those containing electron-withdrawing groups (Cl and NO2). This behavior might be explained by the hydrogen dissociation abilities of metallic Pd nanoparticles affected by the organic linkers.

A one-step synthesis of cyclohexanone acetals from phenol/alcohol mixtures has been explored using bifunctional aluminum borates supported Pd catalysts. Three aluminum borates have been prepared via either a high temperature calcination (9Al2O3·2B2O3) or a self-pressured thermal synthesis (PKU-1 and ABO-X) using various aluminum precursors and boric acid. Well dispersed Pd nanoparticles loaded on these materials show excellent phenol hydrogenation activity in both water and ethanol. The reactivity follows the trend of Pd/ABO-X > Pd/9Al2O3·2B2O3 > Pd/PKU-1, which is similar to the sequence of BO4/BO3 ratio presented in the aluminoborates as shown by NMR spectra. When ethanol is used as a solvent, 13.5 % yield of cyclohexanone diethyl acetal has been obtained under the conditions investigated on Pd/ABO-X, which is attributed to its high activity in both hydrogenation and acetalization for the one-step synthesis of cyclohexanone acetals.

MIL-140-type metal organic frameworks (isoreticular zirconium oxide MOFs) with different aromatic moieties (phenyl, naphthalene, and biphenyl) have been synthesized and employed as the supports of palladium nanoparticles (Pd NPs). The catalysts were characterized by XRD, BET, TEM and CO chemisorption. The results reveal that Pd NPs are homogeneously dispersed on all materials whereas different accessibility to CO is observed. The hydrogenation performance in CC saturation with respect to the effect of the aromatic moiety is compared. The Pd/MIL-140A MOF with the highest hydrogenation activity among the three catalysts comprised of different aromatic rings points to a unique Pd–π interaction between Pd and frameworks consisting of mono-phenyl groups (C6H4).The hydrogenation activity of Pd nanoparticles Pd NPs supported on MIL-140 analogs consisting of different aromatic moieties have been explored and the results show that catalysts comprising Pd and a phenyl groups exhibit superior performance to those containing Pd and naphthalene or biphenyl groups.

The hydrogenation activity of 3 wt.% Pd nanoparticles supported on various mono-group (H, OCH3, NH2, Cl, and NO2) substituted Al–MIL-53 materials has been investigated. Substituents enhanced the dispersion of palladium nanoparticles on Al–MIL-53, leading to a narrow particle size distribution in the range of 2 to 4 nm. Pd nanoparticles on fresh catalysts were present as a mixture of Pd(II) and Pd(0) with different ratios. These Pd species readily became metallic in a hydrogen flow even at room temperature. Their activities in hydrogenation of phenol and phenylacetylene are linked to the substituents on the aromatic ring of the framework. Catalysts with electron-donating groups (OCH3 and NH2) show much higher activity than those containing electron-withdrawing groups (Cl and NO2). This behavior might be explained by the hydrogen dissociation abilities of metallic Pd nanoparticles affected by the organic linkers.