Hydroxyapatite as a novel support for Ru in the hydrogenation of levulinic acid to γ-valerolactone

Metal catalysts (Ru, Pt, Pd, Ni) supported on hydroxyapatite (HAP) were examined for the hydrogenation of levulinic acid to γ-valerolactone. Among these Ru supported on HAP exhibited 99% yield of γ-valerolactone at 70 °C and 0.5 MPa H₂ pressure. The Ru/HAP catalyst was characterized by various adsorption and spectroscopic techniques. The Ru/HAP catalyst was quite stable up to four recycles.     

Microwave-assisted reduction of levulinic acid with alcohols producing γ-valerolactone in the presence of a Ru/C catalyst

γ-Valerolactone can be synthesized by reduction of levulinic acid and its esters in the presence of secondary alcohols as hydrogen donors and Ru/C as catalyst. The reaction rate increases when using microwave heating. Quantitative formation of γ-valerolactone was observed within 25 min at 160 °C under microwave heating based on levulinic acid and i-propanol. The reaction appears to proceed via a dehydrogenation–hydrogenation sequence.     

Pd/C catalyzed conversion of levulinic acid to γ-valerolactone using alcohol as a hydrogen donor under microwave conditions

Levulinic acid can be converted to γ-valerolactone in 83–86% yield under microwave heating with 10 mg of 5% Pd/C per mmol levulinic acid as the catalyst and 2.0 equivalents of KOH in ethanol or iso-propanol. The alcohol is used as the hydrogen source as well as the solvent. Pd/C catalyst could be reused for five catalytic cycles without appreciable loss in activity.     

Aqueous-phase hydrogenation of biomass-derived itaconic acid to methyl-γ-butyrolactone over Pd/C catalysts: Effect of pretreatments of active carbon

The effect of active carbon pretreatment on the catalytic performance of Pd/C catalysts in the hydrogenation of itaconic acid was studied. The catalysts were prepared by deposition–precipitation and characterized by XRD, BET, NH₃-TPD, TEM and FT-IR. Due to the modification of the surface functional groups, surface structure and surface acidities of active carbon via pretreatment, the Pd/C catalysts showed varied catalytic performances. High dispersion and uniform particles were conducive to the excellent activity of Pd/C catalyst with support copretreated with HNO₃ and NaClO, which exhibited 89.5% selectivity towards methyl-γ-butyrolactone at 180 °C, 4 MPa H₂ for 20 h.     

Platinum/3,3´-thiodipropionic acid nanoparticles as recyclable catalysts for the selective hydrogenation of trans-cinnamaldehyde

Platinum nanoparticles as spherical aggregates were prepared by the reduction of a Pt(II) salt with hydrazine using 3,3´-thiodipropionic acid as a protective agent, and characterized by IR, XRF, XRD, and SEM where agglomerates have been visualized. The average crystallite size was 6 nm. For the first time such nanoparticles were evaluated as catalysts in the hydrogenation of unsaturated aldehydes. Hydrogenation of trans-cinnamaldehyde yielded cinnamyl alcohol with a selectivity of up to 83% at complete substrate conversion. At 30 °C, the catalyst could be recycled and reused for three runs with only slight losses in activity and selectivity.     

Development of an integrated process for the production of high-purity γ-aminobutyric acid from fermentation broth

γ-Aminobutyric acid (GABA), a natural non-protein amino acid, plays an irreplaceable role in regulating the life activities of organisms. Nowadays, the separation and purification of food-grade GABA from fermentation broth is still a great challenge. This research utilized monosodium glutamate as a substrate for the production of high-purity GABA via an integrated process incorporating fermentation, purification, and crystallization. Firstly, 147 g·L^-1 GABA with a yield of 99.8% was achieved through fed-batch fermentation by Lactobacillus brevis CE701. Secondly, three integrated purification methods by ethanol precipitation were compared, and crude GABA with a purity of 89.85% was obtained by the optimized method. Thirdly, GABA crystals with a purity of 98.69% and a yield of 60% were further obtained through a designed crystallization process. Furthermore, the GABA industrial production process model was established by Superproper Designer V10 software, and material balance and economic analysis were carried out. Ethanol used in the process was recovered with a recovery of 98.79% through Aspen simulated extractive distillation. Then the fixed investment (equipment purchase and installation costs) for an annual production of 80 t GABA will be about 833000 USD; the total annual production cost (raw material cost and utility cost) will be about 641000 USD. The annual sale of GABA may be at the range of 2400000-4000000 USD and the payback period will be about 1-2 year. This integrated process provides a potential way for the industrial-scale production of food-grade GABA.     

Esterification of levulinic acid to ethyl levulinate over bimodal micro–mesoporous H/BEA zeolite derivatives

A series of bimodal micro–mesoporous H/BEA zeolite derivatives were prepared by the post-synthesis modification of H/BEA zeolite by NaOH (0.05 M–1.2 M) treatment. Samples were characterized by powder XRD, low temperature nitrogen adsorption/desorption, temperature programmed desorption of ammonia and ICP. The mesopore formation was found to play a crucial role in liquid phase esterification of levulinic acid with ethanol. The enhanced catalytic activity of a bimodal micro–mesoporous H/BEA zeolite derivative (H/BEA_0.10) prepared by treatment with 0.1 M NaOH can be mainly attributed to the high mesoporosity coupled with better preserved crystallinity and acidic properties.     

Beneficial effect of adding γ-AlOOH to the γ-Al2O3 washcoat of a PdO catalyst for methane oxidation

The beneficial effect of adding γ-AlOOH to the γ-Al₂O₃ washcoat of a ceramic cordierite (2MgO · 2Al₂O₃ · 5SiO₂) monolith, used to support a PdO catalyst, is reported for methane oxidation in the presence of water at low temperature (<500°C). The mini-monolith (400 cells per square inch (CPI), 1 cm diameter × 2.54 cm length; ~52 cells) was washcoated using a suspension of γ-Al₂O₃ plus boehmite (γ-AlOOH), followed by calcination and then deposition of Pd by wet impregnation. An optimum solid content of 25 wt% in the washcoat suspension was used to obtain a ~25 wt% washcoat on the monolith. The presence of γ-AlOOH enhanced the thermal and mechanical stability of the washcoat, provided that the γ-AlOOH content was <8 wt%. Temperature-programmed methane oxidation (TPO) showed that the addition of γ-AlOOH to the γ-Al₂O₃ washcoat decreased the catalyst activity. However, when H₂O (2 vol% and 5 vol%) was present in the feed gas, the γ-AlOOH improved the catalyst activity and stability. A γ-AlOOH content of ~5 wt% in the washcoat was determined to provide the highest catalyst activity and stability for CH₄ oxidation in the presence of water.     

SO4–ZrO2 catalysts for the esterification of benzoic acid to methylbenzoate

SO₄–ZrO₂ catalysts, prepared by varying the conditions of oxide preparation and H₂SO₄ impregnation, have been characterized by means of different techniques (XRD, BET, Hammett–Bertolacini technique, XPS). The esterification of benzoic acid to methylbenzoate has been used to test the different catalysts and their catalytic performance has been discussed in the light of their bulk and surface properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

The activation mechanism of oxalic acid on γ-alumina and the formation of α-alumina

Converting the γ phase into the α phase completely is necessary in the presintering stage of industrial alumina (Al₂O₃), which requires high temperature and energy consumption. To reduce the presintering temperature, γ-Al₂O₃ was activated by oxalic acid. XRD, ²⁷Al-MAS-NMR and TG-DSC were used to characterize the γ - alumina before and after activation, and the phase transformation was studied. The formation temperature of α-Al₂O₃ decreased to 1029 °C for oxalic acid activated γ-Al₂O₃, and the α-fraction was 100% for activated γ-Al₂O₃ at 1300 °C. After oxalic acid activation, the diffraction peak intensity of γ-Al₂O₃ decreased significantly; the results of ²⁷Al-MAS-NMR suggested that octahedral [AlO₆] in γ-Al₂O₃ was easier than tetrahedral [AlO₄] to be attacked by oxalic acid, and the formation of pentavalent [AlO₅] with higher reaction activity, which was in favour of the lowering formation temperature of α-Al₂O₃. The dissolution concentration of Al increased after oxalic acid activation, and the dissolution process was controlled by surface reactions. Oxalic acid mainly attacked the octahedral aluminium in γ-Al₂O₃ and extracted Al as three complexes of [Al(C₂O₄)]⁺, [Al(C₂O₄)₂]^- and [Al(C₂O₄)₃]^3-. Oxalic acid activated γ - Al₂O₃ with a lower phase transformation temperature has broad application prospects in the alumina industry.     

EXAFS characterization of bimetallic Pt–Pd/SiO2–Al2O3 catalysts for hydrogenation of aromatics in diesel fuel

Bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts exhibited much higher activities in aromatic hydrogenation of distillates than monometallic Pt/SiO₂–Al₂O₃ and Pd/SiO₂–Al₂O₃ catalysts. The studies of extended X‐ray absorption fine structure (EXAFS) indicated that there was an interaction between Pt and Pd in the Pt–Pd/ SiO₂–Al₂O₃ catalyst. Furthermore, from the EXAFS, it was assumed that the active metal particle on the Pt–Pd/SiO₂–Al₂O₃ catalysts is composed of the “Pd dispersed on Pt particle” structure. Regarding both the activities of aromatic hydrogenation and the EXAFS results, it was concluded that the Pd species dispersed on Pt particles were responsible for the high activity of the bimetallic Pt–Pd/SiO₂–Al₂O₃ catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modulation of the textures and chemical nature of C–SiC as the support of Pd for liquid phase hydrogenation

A C–SiC composite with a thin layer of carbon surrounding the SiC substrate has been produced by the reaction of SiC with CCl₄. The pore structures, graphitization levels and the chemical compositions can be finely modulated by the synthesis temperature, and atmosphere. A higher synthesis temperature accelerates the chlorination rate, increases the thickness of carbon layers and enhances their graphitization. Mesopores can be generated in C–SiC composites in comparison to predominant micropores in commercial activated carbon (AC), particularly in the presence of reactive atmosphere such as CO₂ and NH₃. Furthermore, with cofeeding of NH₃ with CCl₄, N heteroatoms can be incorporated into the carbon layer and the N content varies in a range of 4.7–9.5 at.%, depending on the synthesis conditions. Both increased fraction of mesopores and their sizes, as well as N doping facilitate significantly hydrogenation of 4-carboxybenzaldehyde. The activity of Pd catalyst supported on N-doped C–SiC is five times that on commercially used AC under the same conditions.     

Synergistic bimetallic Ru–Pt catalysts for the low-temperature aqueous phase reforming of ethanol

Aqueous phase reforming (APR) of ethanol has been studied over a series of Ru and Pt catalysts supported on carbon and titania, with different metal loadings and particle sizes. This study proposed that, on both metals, ethanol is first dehydrogenated to acetaldehyde, which subsequently undergoes C C cleavage followed by different paths, depending on the catalyst used. For instance, although monometallic Pt has high selectivity toward H₂ via dehydrogenation, it has a low efficiency for C C cleavage, lowering the overall H₂ yield. Large Ru particles produce CH₄ through methanation, which is undesirable because it consumes H₂. Small Ru particles have lower activity but higher selectivity toward H₂ rather than CH₄. On these small particles, CO blocks low-coordination sites, inhibiting methanation. The combination of the two metals in bimetallic Ru–Pt catalysts results in improved performance, benefiting from the desirable properties of each Ru and Pt, without the negative effects of either. © 2018 American Institute of Chemical Engineers AIChE J, 65: 151–160, 2019     

Effects of calcination temperature on performance of Cu–Zn–Al catalyst for synthesizing γ-butyrolactone and 2-methylfuran through the coupling of dehydrogenation and hydrogenation

The results of the coupling process over Cu–Zn–Al catalysts show that the different calcination temperature has significant effect on catalytic performance. Lower temperature cannot facilitate the precursor to complete decomposition and higher calcination temperature will decline the surface area of the catalyst, which finally decline the yield for desired products. It is worth mentioning that the specific activities for BDO and furfural conversions are improved at high calcination temperature, but the simultaneous loss of surface area offsets the gain in specific activity and finally causes the decline in the overall activity of catalyst. In contrast to this, the specific activities for 2-methylfuran and tetrahydrofuran formation dramatically decrease when the calcination temperature reaches 750 °C. This strongly indicates that the active sites of the catalyst for 2-methylfuran and tetrahydrofuran formation were significantly destroyed at calcination temperature higher than 750 °C, and these sites are different from those for γ-butyrolactone and furfuryl alcohol formation.     

Influence of pH on the preparation of monometallic rhodium and platinum,and bimetallic RhodiumPlatinum Catalysts supported on γ-Alumina

¹⁹⁵PtNMR and Raman experiments indicated that H₂PtCl₆ adsorbed monomolecularly on the surface of alumina up to a loading of 1 μmol m⁻² during pore volume impregnation. Above this limit crystalline H₂PtCl₆ was formed during the subsequent drying procedure. Adsorption experiments showed that RhCl₃ exhibited the same behaviour, with an even larger monomolecular coverage. The coverage of both metal complexes was dependent on the pH during adsorption and decreased with decreasing pH, due to a shift in the bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the support surface. Because of the acidic properties of RhCl₃ and H₂PtCl₆, the amounts of rhodium and platinum adsorbed during co-adsorption were smaller than during adsorption of the separate metal complexes. The reduction of RhCl₃+H₂PtCl₆ supported on Al₂O₃ was governed by mobile rhodium atoms and small bimetallic clusters. Large metal salt crystals smothered the reduction process.