Elucidation of the Catalytic Pathway for the Direct Conversion of Furfuryl Alcohol into γ-Valerolactone over Al2O3-SiO2 Catalysts.

The one-pot conversion of furfuryl alcohol (FA) into GVL was investigated over the sol-gel-synthesized Al2O3-SiO2 (AlSi) catalysts with various Al2O3 loadings (0.2-10 wt %) and commercial zeolites including MFI-1, H-ZSM5, H-beta, and HY-15 in a batch reactor under mild reaction conditions (130 °C, 1 bar N2, and 15-120 min). The reaction pathways depend largely on the acid properties of the catalysts, especially the types of Bronsted (B) and Lewis (L) acid sites. A tandem alcoholysis/hydrogenation/cyclization sequence is dominant on the AlSi catalysts (Al ≥ 4%) and all the zeolites except MFI-1, resulting in complete conversion of FA and GVL with an yield 64-75% with IPL as the major side-product, regardless of the differences in their B/L ratios 0.06-1.35. In the absence of B acid sites (i.e., 0.2% AlSi and MFI-1 catalysts), FA could be straightforwardly converted into GVL on the weak Lewis acid sites from the isolated silanol groups using 2-propanol as a hydrogen source. The AlSi catalysts are promising tunable catalysts for FA conversion with good recyclability.

Influence of Highly Stable Ni2+ Species in Ni Phyllosilicate Catalysts on Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Enhancing the catalytic performance of non-noble Ni catalysts in the selective hydrogenation of furfural to furfuryl alcohol (FA) in terms of furfural conversion, selectivity, and good recyclability is challenging. Here, spherical nickel phyllosilicate catalysts (Ni_PS) with fibrous-like structures are prepared via a modified sol-gel method with Ni loadings of 2-30 wt %. Upon exposure to air, all the reduced Ni_PS catalysts exhibit more than 80% Ni0/Niphyllosilicate species on the surface, whereas a large portion of Ni oxide species (>55%) is presented on the impregnated catalyst. The Ni2+ species in nickel phyllosilicate catalysts are active and highly stable during reduction, reaction, and regeneration, yielding stable catalytic performance for multiple recycle tests in furfural hydrogenation to FA. Furfural conversion over the Ni_PS catalysts increased monotonically with increasing Ni loading without an FA selectivity drop. The presence of both metallic Ni0 and Niphyllosilicate also produces a synergistic promotional effect for FA formation.

Room Temperature Nanographene Production via CO2 Electrochemical Reduction on the Electrodeposited Bi on Sn Substrate.

Electrochemical reduction of carbon dioxide (CO2RR) to crystalline solid carbon at room temperature is challenging, but it is a providential CO2 utilization route due to its indefinite storage and potential applications of its products in many advanced technologies. Here, room-temperature synthesis of polycrystalline nanographene was achieved by CO2RR over the electrodeposited Bi on Sn substrate prepared with various bismuth concentrations (0.01 M, 0.05 M, and 0.1 M). The solid carbon products were solely produced on all the prepared electrodes at the applied potential -1.1 V vs. Ag/AgCl and were characterized as polycrystalline nanographene with an average domain size of ca. 3-4 nm. The morphology of the electrodeposited Bi/Sn electrocatalysts did not have much effect on the final structure of the solid carbon products formed but rather affected the CO2 electroreduction activity. The optimized negative potential for the formation of nanographene products on the 0.05Bi/Sn was ca. -1.5 V vs. Ag/AgCl. Increasing the negative value of the applied potential accelerated the agglomeration of the highly reactive nascent Bi clusters in situ formed under the reaction conditions, which, as a consequence, resulted in a slight deviation of the product selectivity toward gaseous CO and H2 evolution reaction. The Bi-graphene composites produced by this method show high potential as an additive for working electrode modification in electrochemical sensor-related applications.

Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction.

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction reactions (CO2RR) are demonstrated. Under a ternary electrolyte system containing [BMIm]+[BF4]-, propylene carbonate, and water, a mixture of sp2/sp3 carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C-C coupling reaction of CO2RR (10-390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp3-rich carbon and diamond seed formation; stage 2: diamond growth and diamond-graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO2 and high selectivity for the solid carbon products (>95%) were maintained during the full CO2RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO2 emission technology.

Aqueous-phase Selective Hydrogenation of Furfural to Furfuryl Alcohol over Ordered-mesoporous Carbon Supported Pt Catalysts Prepared by Onestep Modified Soft-template Self-assembly Method.

Ordered mesoporous carbon (OMC) has attracted a great deal of attention as catalyst support due to their tunable morphological and textural properties. In this study, the characteristics and catalytic properties of OMC-supported Pt catalysts prepared by one-step modified soft-template self-assembly method (Pt/OMC-one-pot) were compared to the Pt impregnated on OMC, activated carbon (AC), and nonuniform meso/macroporous carbon (MC) in the selective hydrogenation of furfural to furfuryl alcohol (FA) under mild conditions (50°C, 2 MPa H2). Larger Pt particle size (~4 nm) was obtained on the Pt/OMC-one-pot comparing to all the impregnated ones, in which the Pt particle sizes were in the range 0.5 - 2 nm. Reduction step was not necessary on the Pt/OMC-one-pot and among the catalysts studied, the Pt/OMC-one-pot exhibited the highest furfural conversion and FA selectivity under aqueous conditions. The use of methanol as the solvent resulted in the formation of solvent product (2-furaldehyde dimethyl acetal) instead. The amount of Pt being deposited, location of Pt particles, and metal-support interaction strongly affected recyclability of the catalysts because some larger size Pt particles with weak metal-support interaction could be leached out during the liquid-phase reaction, rendering similar catalytic performances of the various porous carbon supported catalysts after the 3rd cycle of run.

Sequential electrodeposition of Cu-Pt bimetallic nanocatalysts on boron-doped diamond electrodes for the simple and rapid detection of methanol.

In this work, a novel electrochemical sensor for methanol determination was established by developing a bimetallic catalyst with superiority to a monometallic catalyst. A Cu-Pt nanocatalyst was proposed and easily synthesized by sequential electrodeposition onto a boron-doped diamond (BDD) electrode. The successful deposition of this nanocatalyst was then verified by scanning electron microscopy and energy dispersive spectroscopy. The electrodeposition technique and sequence of metal deposition significantly affected the surface morphology and electrocatalytic properties of the Cu-Pt nanocatalyst. The presence of Cu atoms reduced the adsorption of other species on the Pt surface, consequently enhancing the long-term stability and poisoning tolerance of Pt nanocatalysts during the methanol oxidation process. This advanced sensor was also integrated with sequential injection analysis to achieve automated and high-throughput analysis. This combination can significantly improve the detection limit of the developed sensor by approximately 100 times compared with that of the cyclic voltammetric technique. The limit of detection of this sensor was 83 µM (S/N = 3), and wide linearity of the standard curve for methanol concentrations ranging from 0.1 to 1000 mM was achieved. Finally, this proposed sensor was successfully applied to detect methanol in fruit and vegetable beverage samples.

Effect of the Nanostructured Zn/Cu Electrocatalyst Morphology on the Electrochemical Reduction of CO2 to Value-Added Chemicals.

Zn/Cu electrocatalysts were synthesized by the electrodeposition method with various bath compositions and deposition times. X-ray diffraction results confirmed the presence of (101) and (002) lattice structures for all the deposited Zn nanoparticles. However, a bulky (hexagonal) structure with particle size in the range of 1-10 µm was obtained from a high-Zn-concentration bath, whereas a fern-like dendritic structure was produced using a low Zn concentration. A larger particle size of Zn dendrites could also be obtained when Cu2+ ions were added to the high-Zn-concentration bath. The catalysts were tested in the electrochemical reduction of CO2 (CO2RR) using an H-cell type reactor under ambient conditions. Despite the different sizes/shapes, the CO2RR products obtained on the nanostructured Zn catalysts depended largely on their morphologies. All the dendritic structures led to high CO production rates, while the bulky Zn structure produced formate as the major product, with limited amounts of gaseous CO and H2. The highest CO/H2 production rate ratio of 4.7 and a stable CO production rate of 3.55 µmol/min were obtained over the dendritic structure of the Zn/Cu-Na200 catalyst at -1.6 V vs. Ag/AgCl during 4 h CO2RR. The dissolution and re-deposition of Zn nanoparticles occurred but did not affect the activity and selectivity in the CO2RR of the electrodeposited Zn catalysts. The present results show the possibilities to enhance the activity and to control the selectivity of CO2RR products on nanostructured Zn catalysts.

Effects of TiO2 structure and Co addition as a second metal on Ru-based catalysts supported on TiO2 for selective hydrogenation of furfural to FA.

The TiO2 supported Ru-based catalysts were prepared with 1.5 wt% Ru and 0-0.8 wt% Co on various TiO2 (anatase, rutile, P-25, and sol-gel TiO2) and studied in the liquid-phase selective hydrogenation of furfural to furfuryl alcohol (FA) under mild conditions (50 °C and 2 MPa H2). The presence of high anatase crystallographic composition on TiO2 support was favorable for enhancing hydrogenation activity, while the strong interaction between Ru and TiO2 (Ru-TiOx sites) was required for promoting the selectivity to FA. The catalytic performances of bimetallic Ru-Co catalysts were improved with increasing Co loading due to the synergistic effect of Ru-Co alloying system together with the strong interaction between Ru and Co as revealed by XPS, H2-TPR, and TEM-EDX results. The enhancement of reducibility of Co oxides in the bimetallic Ru-Co catalysts led to higher hydrogenation activity with the Ru-0.6Co/TiO2 catalyst exhibited the best performances in FA selective hydrogenation of furfural to FA under the reaction conditions used.

Identification of extremely hard coke generation by low-temperature reaction on tungsten catalysts via Operando and in situ techniques.

The coke formation in the catalytic system mainly cause to the catalyst deactivate resulting the dramatic decreasing of the catalyst performance then the catalyst regeneration was required. In this study, adding MgO physically mixed with WO3/SiO2 catalysts were prepared and compared with the ones prepared by physically mixing with SiO2. Adding MgO affected the generation of new species of coke deposited on WO3/SiO2 and MgO itself. Comparing the reaction temperature when adding MgO between at 300 and 450 °C, the different pathway of reaction and the coke formation were found. At 450 °C, the metathesis reaction was more pronounced and the lower temperature of coke deposited on WOx/SiO2 was found. Surprisingly, the extremely hard coke occurred during reaction at 300 °C that the maxima of coke formation was found over 635 °C. This due to the fact that the reduction of reaction temperature from 450 to 300 °C affected the decreasing of the metathesis activity. Conversely, the increasing of dimerization and isomerization of butenes-isomer was observed especially 1-butene and iso-butene. Thus, it could suggest that those quantity of them play the important role to generate the charged monoenyl or cyclopentenyl species by participating with ethene through the dimerization, resulting in the formation of extremely hard coke.

Role of Al in Na-ZSM-5 zeolite structure on catalyst stability in butene cracking reaction.

The Na-ZSM-5 catalysts (SiO2/Al2O3 molar ratio = 20, 35, and 50) were prepared by rapid crystallization method to investigate their performance in butene cracking reaction. The XRD, XRF, NH3-TPD, FT-IR, TPO, UV-Vis, and 1H, 27Al, 29Si MAS NMR techniques were used to identify the physical and chemical properties of Na-ZSM-5 catalysts. The silanol group (Si-OH) was the main acid site of Na-ZSM-5, and it was proposed to be the active site for the butene cracking reaction. The butene conversion and coke formation were associated with the abundance of silanol groups over the Na-ZSM-5 catalyst. The dealumination, resulting in the deformation of tetrahedral framework aluminum species was a key factor for Na-ZSM-5 catalyst deactivation, because of the Si-O-Al bond breaking and formation of Si-O-Si bond. The stability of the Si-O-Al bond was linked to the molar number of sodium since the Na atom interacts with the Si-O-Al bond to form Si-ONa-Al structure, which enhances the stability of the silanol group. Therefore, the Si-ONa-Al in zeolite framework was an essential structure to retain the catalyst stability during the reaction. The Na-ZSM-5 with the lowest SiO2/Al2O3 molar ratio showed the best performance in this study resulting the highest propylene yield and catalyst stability.

Synthesis and Characteristics of CaO/MgO Mixed Oxides for the Double Bond Isomerization of 1-Butene.

The MgO catalysts containing only weak/medium basic sites were doped with a strong basic oxide CaO by co-precipitation method with 0.19-3.64 wt% CaO. While the amount of strong basic sites linearly increased with wt.% CaO, the activity for isomerization of 1-butene to 2-butenes of the CaO-doped MgO catalysts was maximized at 1.77 wt% CaO. Addition of a small amount of CaO-dopant altered the MgO structure (i.e., the formation of step, edge, and corner sites), resulting in different OH- adsorption abilities and enhanced catalytic activities.

Effects of calcination and pretreatment temperatures on the catalytic activity and stability of H2-treated WO3/SiO2 catalysts in metathesis of ethylene and 2-butene.

The effects of calcination and pretreatment temperatures of the H2-treated WO3/SiO2 catalysts in metathesis of ethylene and 2-butene to propylene were investigated. The results showed that pretreatment with pure hydrogen over the non-calcined catalysts resulted in higher activity and stability than the calcined catalysts, and the hydrogen pretreatment temperature at 650 °C offered the highest 2-butene conversion and propylene selectivity. The calcination of the catalyst before hydrogen pretreatment was proved to be unnecessary. As revealed by various characterization results from N2 physisorption, XRD, TEM, UV-Vis, Raman, in situ H2-TPR, in situ NH3-DRIFTS and in situ NH3-TPD techniques, activity of the metathesis of ethylene and 2-butene to propylene was related to tungsten dispersion on the support, WO2.83 and WO2 phase composition, and isolated surface tetrahedral tungsten oxide species. The stability of the metathesis reaction was also related to the total acidity and the acid sites of both Brønsted and Lewis acid sites.

Effect of pretreatment atmosphere of WO x /SiO2 catalysts on metathesis of ethylene and 2-butene to propylene.

The effect of a gas pretreatment atmosphere (pure N2, pure H2 and mixed H2/N2) on the metathesis reaction between ethylene and 2-butene to propylene over calcined and non-calcined WO3/SiO2 catalysts was investigated. The non-calcined catalysts exhibited higher activity than the calcined catalysts under different gas pretreatment atmospheres. The non-calcined catalyst with the use of pure H2 pretreatment showed the highest catalytic performances. As revealed by various characterization results from N2 physisorption, XRD, XPS, TEM, SEM-EDX, UV-Vis, Raman, H2-TPR, and NH3-TPD techniques, the WO2.83 phase occurring from the H2 pretreatment of the non-calcined catalyst played an important role on the high activity of the catalyst. In addition, better tungsten dispersion, higher isolated surface tetrahedral tungsten oxide species, and W5+ species were obtained on the H2-treated non-calcined WO3/SiO2 catalyst.

Liquid-phase hydrogenation of phenylacetylene over the nano-sized Pd/TiO2 catalysts.

Understanding the mechanisms of metal-support interaction and/or adhesion and growth of the metal particles is important not only in the field of catalysis but also the design of advanced nanostructure materials. In the present work, the strong metal-support interaction (SMSI) effect occurred on the Pd/TiO2 catalysts synthesized by the sonochemical method when reduced at 500 degrees C whereas the ones prepared by the conventional impregnation resulted in sintering of Pd0 particles instead. The presence of SMSI was correlated to the amount of oxygen vacancies or Ti3+ defective sites. Smaller Pd0 particles with more uniform size distribution on the sonochemical-derived catalysts may promote hydrogen spillover from Pd0 surface to TiO2 support so that the reduction of Ti4+ to Ti3+ occurred, resulting in the SMSI. As a consequence, the catalysts exhibited improved catalytic performances in the liquid-phase selective hydrogenation of phenylacetylene to styrene.

Improvement of early cell adhesion on Thai silk fibroin surface by low energy plasma.

Low energy plasma has been introduced to treat the surface of Thai silk fibroin which should be enhanced for cell adhesion due to its native hydrophobic surface. Plasma surface treatment could introduce desirable hydrophilic functionalities on the surface without using any chemicals. In this work, nitrogen glow discharge plasma was generated by a low energy AC50Hz power supply system. The plasma operating conditions were optimized to reach the highest nitrogen active species by using optical emission spectroscopy. X-ray photoelectron spectroscopy (XPS) revealed that amine, hydroxyl, ether, and carboxyl groups were induced on Thai silk fibroin surface after plasma treatment. The results on Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy confirmed that the plasma treated effects were only on the outermost layer since there was no change in the bulk chemistry. The surface topography was insignificantly changed from the detection with atomic force microscopy (AFM). The plasma-treated effects were the improved surface wettability and cell adhesion. After a 90-s treatment, the water contact angle was at 20°, while the untreated surface was at 70°. The early cell adhesion of L929 mouse fibroblast was accelerated. L929 cells only took 3h to reach 100% cell adhesion on 90 s N2 plasma-treated surface, while there was less than 50% cell adhesion on the untreated Thai silk fibroin surface after 6h of culture. The cell adhesion results were in agreement with the cytoskeleton development. L929 F-actin was more evident on 90 s N2 plasma-treated surface than others. It could be concluded that a lower energy AC50Hz plasma system enhanced early L929 mouse fibroblast adhesion on Thai silk fibroin surface without any significant change in surface topography and bulk chemistry.

Characteristics and catalytic behavior of Pd catalysts supported on nanostructure titanate in liquid-phase hydrogenation.

Titanate nanowire (TNW) and nanotube (TNT) structures were synthesized by the hydrothermal reaction using spherical shape anatase TiO2 nanoparticles (TNP) as the starting material and employed as Pd catalyst supports for the liquid-phase selective hydrogenation of 1-heptyne to 1-heptene. Pd dispersion was significantly improved as the specific surface area of the supports increased in the order: Pd/TNT > Pd/TNW >> Pd/TNP. While the hydrogenation rate increased with increasing number of active Pd(0) surface, the selectivity to 1-heptene depended largely on the degree of interaction between Pd and the supports. The catalysts prepared by impregnation method led to a stronger metal-support interaction than those prepared by colloidal route. The selectivity of 1-heptene at complete conversion of 1-heptyne was obtained in the order: I-Pd/TNT > I-Pd/TNP >pd/TNT approximately Pd/TNW > Pd/TNP.

Effect of TiO2 crystalline phase composition on the physicochemical and catalytic properties of Pd/TiO(2) in selective acetylene hydrogenation.

Pd/TiO(2) catalysts have been prepared using TiO(2) supports consisting of various rutile/anatase crystalline phase compositions. Increasing percentages of rutile phase in the TiO(2) resulted in a decrease in Brunauer-Emmett-Teller surface areas, fewer Ti(3+) sites, and lower Pd dispersion. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti(3+) in the TiO(2) samples. When TiO(2) samples with 0-44% rutile were used, high ethylene selectivities (58-93%) were obtained whereas ethylene losses occurred for those supported on TiO(2) with 85% or 100% rutile phase. X-ray photoelectron spectroscopy and electron spin resonance experiments revealed that a significant amount of Ti(3+) existed in the TiO(2) samples composed of 0-44% rutile. The presence of Ti(3+) in contact with Pd can probably lower the adsorption strength of ethylene resulting in an ethylene gain. Among the five catalysts used in this study, the results for Pd/TiO(2)-R44 suggest an optimum anatase/rutile composition of the TiO(2) used to obtain high selectivity of ethylene in selective acetylene hydrogenation.