Microwave-assisted catalytic pyrolysis of cellulose for phenol-rich bio-oil production

The microwave-assisted catalytic pyrolysis (MACP) of cellulose was carried out using modified HZSM-5 catalysts for bio-oil production. The catalysts of Fe/HZSM-5, Ni/HZSM-5 and Fe–Ni/HZSM-5 were developed and characterized by the X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The bio-oil was characterized by the Fourier transform infrared analyzer (FTIR) and gas chromatography/mass spectrometry (GC/MS). Results showed that Fe/HZSM-5 enhanced the yields of bio-oil by 11.4% and decreased the coke by about 24% compared to HZSM-5 without modification. The saccharides in bio-oil disappeared and were totally converted into phenols and low molecular compounds with the catalysis of Fe–Ni/HZSM-5. Fe–Ni/HZSM-5 showed high selectivity of phenols (20.86%) in the bio-oil. It was a unique finding because usually phenols can only be obtained by the pyrolysis of lignin, not cellulose. The formation of phenols from MACP of cellulose was probably caused by the conversion of furans to aromatics in the pores of HZSM-5, and followed by further conversion of aromatics into phenols on the external surface of HZSM-5.     

Ultra-low Pt loading catalytic layer based on buckypaper for oxygen reduction reaction

Buckypaper is a freestanding, self-supported and well defined membrane-like black thin film. We developed a buckypaper film containing a MWNTs-rich surface and a CNFs-rich surface. Pt nanoparticles supported on this film with an ultra-low Pt content, 0.05 mg/cm², as a catalytic layer for oxygen reduction reaction (ORR) were synthesized by a sputtering process (Pt/BP-SP). The physical and chemical properties as well as electrochemical performance of this nanocomposite were studied. For comparison, Pt nanoparticles supported on buckypaper with a Pt content of 0.10 mg/cm² were prepared by an electrodeposition process (Pt/BP-ED). The results proved that Pt/BP-SP possessed a smaller particle size and a more uniform distribution on buckypaper than Pt/BP-ED. Cyclic voltammetric investigation showed that Pt/BP-SP had a higher electrochemical surface area although its Pt content was lower than that of Pt/BP-ED. Tafel studies proved that Pt/BP-SP had a move positive equilibrium potential and a higher apparent exchange current density. Moreover, the results of linear sweep voltammetric (LSV) analysis exhibited that Pt/BP-SP had a higher ORR activity compared with Pt/BP-ED, and LSV at different rotation rates revealed that ORR on Pt/BP-SP electrode was a 4e⁻ process.     

Effect of titania synthesis conditions on the catalytic performance of mesoporous Ni/TiO2 catalysts for carbon dioxide reforming of methane

The catalytic performance of 5 wt% Ni/TiO₂ catalysts with different physicochemical properties was studied for the CO₂ reforming of methane reaction. The TiO₂ supports were prepared by the evaporation-induced self-assembly method using three different titania metal precursors. The catalysts were characterized by XRD, BET, TGA, and TEM techniques. The results showed that the phase composition of TiO₂ support plays a crucial role in catalyst performance. Furthermore, the variation of synthesis conditions significantly affects the physicochemical properties of TiO₂ support. NH₃-treatment helped maintain the higher surface area by retaining a significant fraction of the amorphous content of titania support. Catalysts deactivation was caused by the phase transformation of TiO₂ from anatase to rutile and the sintering of Ni metal. Phase transformation into rutile was more significant, with the catalysts possessing a higher content of amorphous TiO₂. Ni/TiO₂ catalyst prepared using the titanium ethoxide precursor performed better in the dry reforming reaction. Anatase titania offers strong metal-support interaction, whereas weak metal-support interaction was observed in the amorphous and rutile phase.     

Investigation on multifunctional Au/TiO2@n-octadecane microcapsules towards catalytic photoreforming hydrogen production and photothermal conversion

Combining solar energy utilization and hydrogen production is an ideal model for renewable energy development. Especially the conversion of broad-spectrum solar energy into chemical energy of hydrogen and thermal energy can enrich solar energy storage methods. Herein, novel multifunctional Au/TiO₂@n-octadecane microcapsules with core-shell structure were design and synthesized by wet chemical reduction and electrostatic adsorption self-assembly methods for photothermal hydrogen production and thermal storage. The results showed that microencapsulation of photothermal catalysts could provide an effective reaction area and excellent dispersion stability, where hydrogen production and light to hydrogen efficiency were increased in the 43% and 0.3% respectively, compared to the nanoparticle suspension system. Based on the recorded temperature variations caused by the photothermal effect, the calculated photothermal conversion efficiency and specific absorption rate of Au/TiO₂@n-octadecane was 25.01% and 277% higher than that of Au/TiO₂ suspension. The proposed hydrogen production and thermal storage method via multifunctional microcapsules might shed some light on the study of improving full-spectrum energy conversion efficiency of solar energy.     

Bio-hydrogen production based on catalytic reforming of volatiles generated by cellulose pyrolysis: An integrated process for ZnO reduction and zinc nanostructures fabrication

The paper presents a process of cellulose thermal degradation with bio-hydrogen generation and zinc nanostructures synthesis. Production of zinc nanowires and zinc nanoflowers was performed by a novel processes based on cellulose pyrolysis, volatiles reforming and direct reduction of ZnO. The bio-hydrogen generated in situ promoted the ZnO reduction with Zn nanostructures formation by vapor-solid (VS) route. The cellulose and cellulose/ZnO samples were characterized by thermal analyses (TG/DTG/DTA) and the gases evolved were analyzed by FTIR spectroscopy (TG/FTIR). The hydrogen was detected by TPR (Temperature Programmed Reaction) tests. The results showed that in the presence of ZnO the cellulose thermal degradation produced larger amounts of H₂ when compared to pure cellulose. The process was also carried out in a tubular furnace with N₂ atmosphere, at temperatures up to 900 °C, and different heating rates. The nanostructures growth was catalyst-free, without pressure reduction, at temperatures lower than those required in the carbothermal reduction of ZnO with fossil carbon. The nanostructures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The optical properties were investigated by photoluminescence (PL). One mechanism was presented in an attempt to explain the synthesis of zinc nanostructures that are crystalline, were obtained without significant re-oxidation and whose morphologies are dependent on the heating rates of the process. This route presents a potential use as an industrial process taking into account the simple operational conditions, the low costs of cellulose and the importance of bio-hydrogen and nanostructured zinc.     

Improved catalytic stability of Pt/TiO2 catalysts for methylcyclohexane dehydrogenation via selenium addition

To improve the catalytic activity of Pt catalysts for methylcyclohexane (MCH) dehydrogenation, which is utilized for hydrogen transportation, the effects of the addition of Se on the performance of Pt/TiO₂ catalysts were investigated. In Se/Pt/TiO₂ catalysts, even a small amount of Se addition (Se/Pt = 0.01) improved the catalyst stability. Se was highly dispersed on the Pt/TiO₂ surface, without volatilizing in a reducing atmosphere at temperatures below 450 °C, and did not form an alloy with Pt. The analysis of adsorption-desorption characteristics revealed that the addition of Se promoted the desorption of products, including the main product, toluene. Moreover, an electron donation effect from Se to Pt was observed by FT-IR measurement after the reduction. The desorption characteristic caused by the electron donation effect suppressed the deterioration of the catalyst and allowed stable catalytic activity toward the MCH dehydrogenation reaction.     

Pt modulates the electronic structure of Pd to improve the performance of Pd-based catalytic combustion catalyst

The electronic modulation between the catalytic active components can improve the catalytic activity and stability of the catalyst. The Pd-based catalysts can easily react with SO_X to form stable and inactive sulfates. In this paper, the Pd–Pt-based catalytic combustion catalyst was prepared by replacing part of Pd with a small amount of Pt. The storage tank VOCs catalytic combustion activity and the anti-SO₂ poisoning performance of the Pd–Pt-based catalyst and Pd-based catalyst were tested. The Pd 3d binding energy of each Pd-based catalyst was detected by XPS characterization, and the electronic structure changes of Pd active components was analyzed by the change of Pd 3d binding energy. The effect of electrons transfer between Pd and Pt on the improvement of catalytic combustion activity and SO₂ poisoning resistance of Pd-based catalysts was analyzed. The results show that the Pt addition can increase the electron cloud density of the Pd active components, and improve the performance of the Pd active components to adsorb and activate oxygen. The reaction of Pd and SO_X to form sulfate needs to gain electrons. The increase in the electron cloud density of the Pd active components in Pd–Pt-based catalyst makes it difficult for the Pd active components to adsorb SO_X and difficult to react with SO_X to form sulfate, thereby preventing the Pd active components from being poisoned and deactivated.     

Pt/C催化剂催化微晶纤维素加氢的研究

通过对Pt/C催化剂催化转化微晶纤维素的研究,探讨了纤维素催化转化的反应机理及反应温度、H2压力、反应时间对纤维素转化率和乙二醇选择性的影响,同时考察了超声波预处理微晶纤维素,讨论了超声时间对微晶纤维素催化加氢转化率的影响。试验结果表明,随着反应温度、H2压力的增大和反应时间的延长,纤维素转化率逐渐增加,在250℃,H2压力为4 MPa,反应2 h时,微晶纤维素的转化率可达到80.08%,乙二醇的选择性为70.02%。随着超声时间的延长,微晶纤维素的转化率逐渐增大,超声20 min后变化不明显。     

Experimental evaluation of Pt/TiO2/rGO as an efficient HER catalyst via artificial photosynthesis under UVB & visible irradiation

The study investigated the synergistic effects of rGO and Pt over TiO₂ for the HER via artificial photosynthesis under UVB and visible light irradiation. The introduction of glycerol and industrial wastewater to the system as sacrificial reductants signifies that the major reaction pathway is photocatalytic partial water splitting. The material characterizations revealed successful heterojunction formation and provided insight into chemistry behind the activity of the photocatalysts. Amongst various combinations of rGO on TiO₂, 1GNT exhibited an HER yield five times that of bare TiO₂ under UVB light. Addition of Pt led to the formation of a strong Schottky barrier at the heterojunction and consequently boosted HER performance. 1P0.5 GT presented the highest of 28.5 mmol g⁻¹ h⁻¹ with glycerol and 9.6 mmol g⁻¹ h⁻¹ with wastewater under UVB light respectively. For both binary and ternary photocatalysts, the HER performances dwindled under visible light irradiation, accentuating the insufficient activation of the TiO₂. In addition, 1PT outperformed all the other photocatalysts thereby elucidating the impression that rGO and Pt does not work well together in enhancing HER despite quenching the exciton recombination rate of TiO₂ significantly. The role of pH in the synthesis and the experiments has been discussed. Finally, the underlying mechanisms in the photodeposition and photoreformation have been proposed.     

Experimental studies on syngas catalytic combustion on Pt/Al2O3 in a microreactor

Synthesis gas (a mixture of CO and H₂) oxidation is studied over a supported Pt/Al₂O₃ catalyst in a novel microreactor fabricated for studying the intrinsic chemical kinetics of highly exothermic reactions. CO was found to significantly inhibit H₂ oxidation. In contrast, H₂ addition promotes CO oxidation at low mole fractions but has a small promoting effect at high hydrogen mole fractions. As a result, the apparent reaction order of H₂ changes from positive to zero. The change in hydrogen reaction order is associated with hysteresis. Possible mechanisms for the observed behavior are discussed.     

Green synthesis of well dispersed TiO2/Pt nanoparticles photocatalysts and enhanced photocatalytic activity towards hydrogen production

Deposition of Pt NPs with preferred dispersion and morphologies on TiO₂ have been the focus of studies in photocatalytic and photoelectrochemical hydrogen production. Green synthesis of TiO₂/Pt NPs nanocomposites with narrow size distribution of Pt NPs still remain a challenge. Herein, we report that sucrose is highly efficient for the preparation of well-dispersed TiO₂/Pt NPs photocatalysts. Moreover, the sucrose could act as an electron donor, showing higher hydrogen production activity under simulated sunlight than pure water. The as-synthesized photocatalysts have been characterized by techniques of transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX), and diffuse reflectance spectroscopy (DRS). Compared with TiO₂/Pt NPs photocatalysts prepared through conventional photodeposition, the photocatalysts as prepared showed higher photocatalytic efficiency. Moreover, the catalyst could be reused easily without apparent degradation of their original photocatalytic activities. This approach presents a promising and low-cost strategy to improve the photocatalytic performance of TiO₂ from biomass.     

The effects of different dimensional carbon additives on performance of PEMFC with low-Pt loading cathode catalytic layers

The addition of carbon additives to the catalytic layers (CLs) with low-Pt loadings significantly improves the cell performance of proton exchange membrane fuel cells. However, the structure-activity relationship between the different dimensional carbon materials in CLs and the cell performance is still unknown. In the present work, three different dimensional carbon materials have been added into the cathode CLs with low Pt loading. The addition of one-dimensional carbon nanotubes and zero-dimensional XC-72R significantly enhanced the power density of the fuel cell because of the improved Pt dispersion and porous structures of the CL. This resulted in enhanced gas transfer and water removal accessibility. Nevertheless, the tortuous transfer path of gas and water after the presence of graphene nanosheet in the CL results in increased mass transfer resistance, although it reduces the charge transfer of the CL due to the improved catalyst utilization at low current density regions of polarization curves.     

Optical and structural properties of TiO2 thin films prepared by sol-gel spin coating

Hydrogen is a renewable and non-polluting fuel. Its production from water using renewable energy is an attractive challenge. In this work we report some results on the preparation of titanium oxide TiO₂ thin films for environmental applications such as water photosplitting. TiO₂ thin films have been prepared by spin coating technique of sol precursor onto glass substrates. The deposited films were annealed at different temperatures in air. The X-ray diffraction (XRD) experiments show that the two well-known anatase and rutile phases were observed depending both on the conditions of deposition and on the temperature of annealing. The best conditions of crystallization were found to be around 400 °C in air. The influence of the number of deposited layer on the crystalline quality of the films was investigated. The surface morphology of the deposited film was characterized by atomic force microscopy (AFM) and scanning electronic microscopy (SEM). The UV-Vis-NIR spectroscopy shows that the film exhibits a high transmission around 90%. The best layers were obtained when concentrated (HCl) was added to the sol solutions. The direct band gap of the films was found to be around 3.7 eV, and their refractive index was found to vary from 2 to 2.4.     

Non-linear kinetic analysis of catalytic hydrolysis of ethylenediamine bisborane with nano-structured Pd/TiO2 catalyst

In this study, the hydrogen generation from catalytic hydrolysis of ethylenediamine bisborane (EDAB) solution catalyzed by nanostructured titanium dioxide (TiO₂) supported Pd metallic catalyst was carried out. TiO₂ support material was synthesized by the sol-gel method from titanium (IV) ethoxide. Pd was loaded into TiO₂ by the conventional impregnation-reduction method and reduction was carried out at 750 °C in an H₂ atmosphere. The characterization of catalysts was done with SEM-EDX and multi-point BET analysis. To investigate the hydrogen production by catalytic hydrolysis of EDAB, parameters such as Pd loading (2–4% by weight) and temperature (40–80 °C) were chosen in the presence of ethylenediamine bisborane aqueous solution (0.034% by weight). Detailed non-linear kinetic analysis was applied to the experimental data by considering and Langmuir-Hinshelwood model and power law. The activation energy E_a was calculated as E_a = 33.61 kJ mol^?1 and E_a = 36.32 kJ mol^?1 according to Langmuir-Hinshelwood and power-law model respectively for the Pd/TiO₂ catalyst.     

Enhancement of the catalytic performance and coke resistance of alcohol-promoted Ni/MCM-41 catalysts for CH4/CO2 reforming

A series of Ni-based catalysts were prepared by the alcohol-promoted impregnation for CO₂ reforming of methane. In order to illuminate the effects of carbon chain numbers and hydroxyl group numbers on the catalytic performance and coke resistance of Ni-based catalysts, the samples were characterized by XRD, SEM, BET, H₂-TPR, FT-IR, XPS, TG, and TEM. The results show that the introduction of alcohol during impregnation promotes Ni²⁺ species into the channels of MCM-41, thereby strengthening the meatal-support interaction. Besides, the presence of alcohol decreases the particle size of Nickel and increases the surface adsorbed oxygen species over the surface of the support, thus promoting the coke resistance of the catalysts. As a consequence, NM-EG shows the highest catalytic performance, the highest stability, and the best coke resistance in all of the catalysts. This indicates that the main factor influencing the catalytic performance and coke resistance of the catalysts is the number of hydroxyl groups rather than the chain length of the introduced alcohol in the alcohol-promoted impregnation.     

Two-dimensional C@TiO2/Ti3C2 composite with superior catalytic performance for NaAlH4

Carbon coated titanium dioxide supported on two-dimensional titanium carbide (C@TiO₂/Ti₃C₂) is synthesized by simple annealing under a flowing acetylene (C₂H₂) atmosphere, and applied to improve the hydriding/dehydriding behavior of sodium alanate (NaAlH₄). The results indicate that as-prepared C@TiO₂/Ti₃C₂ composite exhibits excellent catalytic activity. The initial temperature for hydrogen desorption is reduced by 70 °C compared with the pristine sample. About 4.0 wt% hydrogen is released in 13 min at 140 °C. The apparent activation energies (E_a) of 10 wt% C@TiO₂/Ti₃C₂ catalyzing NaAlH₄ for the first two-steps dehydrogenation are 72.41 and 64.27 kJ mol⁻¹ respectively. The structural analyses reveal that C@TiO₂/Ti₃C₂ interacts with NaAlH₄ by using ball milling and decomposes to form Ti-species which works in combination with carbon to improve the dehydrogenation performance of NaAlH₄. This result provides an important progress in the hydrogen storage of NaAlH₄ catalyzed by MXene.     

A study on the catalytic hydrogenation of N-ethylcarbazole on the mesoporous Pd/MoO3 catalyst

Mesoporous MoO₃ shows an apparent activity in the catalytic hydrogenation of N-ethylcarbazole (NEC), where a significant amount of tetrahydro-N-ethylcarbazole (4H-NEC) and perhydro-N-ethylcarbazole (PNEC) are detected with the hydrogen uptake of 0.97 wt% after 6 h when the temperature rises to 220 °C. 0.5 wt% Pd/MoO₃ catalyst shows a superior catalytic efficiency than the traditional precious metal catalysts 0.5 wt% Ru/Al₂O₃ and 0.5 wt% Pd/Al₂O₃, especially in the conversion of Octahydro-N-ethylcarbazole (8H-NEC) to PNEC. The hydrogenation mechanism of MoO₃ is completely different from the traditional precious metal catalysts. With the presence of a small amount of Pd, the breaking of HH bond is greatly accelerated, result in the promotion of hydrogen spillover rate and the increase of the concentration of hydrogen molybdenum bronze H_xMoO₃, which improves the catalytic efficiency of the MoO₃ catalyst. Rise the temperature also helps increasing the concentration of H in H_xMoO₃.     

Experimental study on fundamental effect of H2 for catalytic soot oxidation with Pt/CeO2 using a flow reactor system

The effect of hydrogen on catalytic soot oxidation was investigated to find new conditions for lowering the regeneration temperature in catalyzed diesel particulate filtration with hydrogen. Soot oxidation experiments using a flow reactor with a Pt/CeO₂ catalyst were carried out to represent catalyzed diesel particulate filtration. Under conditions using more than 6% hydrogen with water, the soot oxidation by hydrogen started at 155 °C for loose contact conditions and at 175 °C for tight contact conditions. The soot oxidation rate tended to increase with increasing concentrations of hydrogen and oxygen. In contrast, no difference was observed with various water concentrations. The HO₂ generated during hydrogen oxidation oxidized soot at low temperature. The soot oxidation temperature of 155 °C was lower than the regeneration temperature in catalyzed diesel particulate filtration reported previously.     

Comparative study of CeO2/CuO and CuO/CeO2 catalysts on catalytic performance for preferential CO oxidation

The CeO₂/CuO and CuO/CeO₂ catalysts were synthesized by the hydrothermal method and characterized via XRD, SEM, H₂-TPR, HRTEM, XPS and N₂ adsorption–desorption techniques. The study shows that the rod-like structure is self-assembled CeO₂, and both hydrothermal time and Ce/Cu molar ratio are important factors when the particle-like CeO₂ is being self-assembled into the rod-like CeO₂. The CuO is key active component in the CO-PROX reaction, and its reduction has a negative influence on the selective oxidation of CO. The advantage of the inverse CeO₂/CuO catalyst is that it still can provide sufficient CuO for CO oxidation before 200 °C in the hydrogen-rich reductive gasses. The traditional CuO/CeO₂ catalyst shows better activity at lower temperature and the inverse CeO₂/CuO catalysts present higher CO₂ selectivity when the CO conversion reaches 100%. The performance of mixed sample verifies that they might be complementary in the CO-PROX system.     

Morphology effect of MnO2 promoter to the catalytic performance of Pt toward methanol electrooxidation reaction

Three MnO₂ samples with different well-defined morphologies including nanoplates, nanorods and corallines are prepared through a simple chemical precipitation method and used as the promoter/support for Pt electrocatalysts (denoted as Pt/MnO₂P, Pt/MnO₂-R and Pt/MnO₂C, respectively). The morphology effects of MnO₂ to the catalytic properties of Pt for methanol oxidation reaction (MOR) are intensively investigated. Results show that the catalytic properties of Pt are strongly dependent on the morphology of the promoter. Pt/MnO₂-R with MnO₂ nanorods as the promoter shows the highest catalytic properties among the MnO₂-promoted catalysts. The mass-specific activity and intrinsic activity of Pt in Pt/MnO₂-R catalyst is 0.51 A mg⁻¹_Pt and 11.54 A m⁻²_Pt, which is ca. 1.89 and 2.18 times that of commercial Pt/C catalysts (0.27 A mg⁻¹_Pt and 5.29 A m⁻²_Pt), respectively. Change in the electronic structure of Pt is responsible for the enhancement in the catalytic properties of Pt/MnO₂-R.