Combination Of Catalyst Research Articles

ZnCo2O4 composite catalyst accelerated removal of phenylic contaminants containing of Cr(VI) in dielectric barrier discharge reactor: Process and mechanism study

The degradation of phenylic contaminants (phenol, hydroquinone, nitrobenzene, p-nitrophenol) containing Cr(VI) has been investigated in a dielectric barrier discharge (DBD) system using a ZnCo2O4 composite catalyst. The ZnCo2O4 nanowires combined with multi-walled carbon nanotubes (MWNTs) on a sponge substrate in the discharge system can induce a decrease in the corona inception voltage and discharge becomes more stable resulting in an improvement in the energy utilization efficiency. With the synergistic degradation of phenylic species containing Cr(VI), the total elimination efficiency was further improved. The active substances (H2O2 and O3) were detected in the discharged solution, and some of them were consumed in the phenylic system. The effects of ·OH, O2·- and e− were also verified using free radical trapping experiments in which ·OH exhibited the main oxidation effect for the degradation of phenylic pollutants, and e−, H2O2 and H· affect the reduction of Cr(VI). The intermediate products were determined in order to analyze the degradation process of phenylic pollutants by the ZnCo2O4 composite catalyst in combination with the DBD system. The electron transfer process in the ZnCo2O4 composite catalyst during discharge was analyzed. Finally, the biotoxicity of the phenylic pollutants before and after degradation was compared.

Rethinking Electronic Effects in Photochemical Hydrogen Evolution Using CuInS2@ZnS Quantum Dots Sensitizers

Molecular catalysts based on coordination complexes for the generation of hydrogen via photochemical water splitting exhibit a large versatility and tunability of the catalytic properties through chemical functionalization. In the present work, we report on light-driven hydrogen production in an aqueous solution using a series of cobalt polypyridine complexes as hydrogen evolving catalysts (HECs) in combination with CuInS2@ZnS quantum dots (QDs) as sensitizers, and ascorbate as the electron donor. A peculiar trend in activity has been observed depending on the substituents present on the polypyridine ligand. This trend markedly differs from that previously recorded using [Ru(bpy)3]2+ (where bpy = 2,2'-bipyridine) as the sensitizer and can be ascribed to different kinetically limiting pathways in the photochemical reaction (viz. protonation kinetics with the ruthenium chromophore, catalyst activation via electron transfer from the QDs in the present system). Hence, this work shows how the electronic effects on light-triggered molecular catalysis are not exclusive features of the catalyst unit but depend on the whole photochemical system.

Possible Fine-Tuning of Methane Activation toward C2 Oxygenates by 3d-Transition Metal-Ions Doped Nano-Ceria-Zirconia.

In this work, we demonstrate a simple sol-gel technique to prepare metal-ion(s)-doped ceria-zirconia solid solution for efficient catalytic methane activation. The cation-depicting formula units are Ce0.80Zr0.20 (CZ), Ce0.79Zr0.20M0.01 (CZM), and Ce0.79Zr0.20M0.005M10.005 (CZMM1) (M and M1 = V, Mn, Fe, Co, and Cu), employed for undoped, mono-metal-ion-doped, and bi-metal-ion-doped solid solutions, respectively. Methane activation with Mn, Fe, Cu mono-metal-ion-doped CZ favors the C1 product, while CZCo assists C-C coupling with the formation of acetaldehyde. On the other hand, the Co- and Fe-doped bi-metal-ion combination catalyst (CZCoFe) shows significant ethanol but predominant formic acid formation. This is further promoted by the Co + V bi-metal-ion combination (CZCoV) catalyst, and it shows ethanol as the major product along with methyl hydrogen peroxide, methanol, and formic acid as minor products. An impressive ethanol yield of 93 μmol/g h with 76% selectivity obtained with the CZCoV catalyst is at par with that obtained with noble-metal-based catalysts under comparable reaction conditions. When Co and V content was increased two and four times from 0.005 to 0.01 and 0.02, ethanol yield increased at the expense of formic acid. The 213 μmol/g h ethanol yield (86% selectivity) observed with Ce0.76Zr0.20Co0.02V0.02 is probably the highest observed. The partial oxidation of CH4 in Co-based bi-metal combinations (Co + V or Co + Fe) suggests the synergistic effect of doped metal ions owing to the heterogeneous near-neighbor environment. The present results are attributed to the surface heterogeneity between the host and the dopants, which selectively promotes methane activation as well as C-C coupling. This indicates a large scope to tune the activity of partial oxidation of methane and product selectivity with different metal-ion(s) combinations.

Chemical transformation of Jojoba oil and Soybean oil and study of their uses as bio-lubricants

Bio-based lubricants have traditionally piqued interest as a supplement to mineral oil-based lubricants in response to rising environmental pollution concerns and declining petroleum assets. This paper discussed the synthesis of bio-lubricants from vegetable oils such as soybean (SOY), and jojoba (JOJ) oil using chemical transformation methods such as epoxidation of the carbon-carbon double bonds in the structure of their already high resistance to air oxidation using a combined catalyst of Amberlite IR 120 and peroxide catalyst with high yield (80 %), followed by transesterification, ring-opening of vegetable oils, and finally acetylation of the hydroxylated obtained products. The rheological and tribological characteristics of the compounds produced were examined to validate their suitability as bio-lubricants using FT-IR, 1H NMR, and TGA techniques. These results demonstrate the possibility of an environmentally sustainable method for producing bio-lubricants.

Kinetics of Catalyzed Thermal Degradation of Polylactide and Its Application as Sacrificial Templates†

Comprehensive SummaryPolylactide (PLA) is an outstanding sacrificial template material for the manufacture of microchannels in a thermosetting matrix. However, the initial thermal degradation temperature of pure PLA is relatively high (about 280°C), which limits its use as a sacrificial template. In this report, we found that TBD, an organic base catalyst, can significantly reduce the thermal degradation temperature of PLA. TBD has higher catalytic activity for the thermal degradation of PLA compared with Tin(II) oxalate (Sn(Oxa)), one catalyst reported in the literature. Moreover, the gaseous products catalyzed by TBD for PLA thermal degradation are mainly lactide, and the formation temperature of the monomer is lower and the yield is higher, which may have potential value for PLA recycling. A combined catalyst, S8T2, was composed of 80% low activity catalyst Sn(Oxa) and 20% high activity catalyst TBD, which can catalyze the rapid degradation of PLA without greatly damaging the mechanical properties of PLA. PLA‐S8T2 sacrificial fibers can form high‐precision one‐dimensional microchannels in the epoxy resin matrix, and 3D‐printed PLA‐S8T2 sacrificial templates can be used to form three‐dimensional microchannels in a thermosetting matrix by vaporization of sacrificial components process (VaSC). These features highlight the great potential of PLA‐S8T2 as sacrificial template material for the preparation of the complicated microchannels in the thermosetting matrix.

Photoinitiated Olefin Metathesis and Stereolithographic Printing of Polydicyclopentadiene

Recent progress in photoinitiated ring-opening metathesis polymerization (photoROMP) has enabled the lithographic production of patterned films from olefinic resins. Recently, we reported the use of a latent ruthenium catalyst (HeatMet) in combination with a photosensitizer (2-isopropylthioxanthone) to rapidly photopolymerize dicyclopentadiene (DCPD) formulations upon irradiation with UV light. While this prior work was limited in terms of catalyst and photosensitizer scope, a variety of alternative catalysts and photosensitizers are commercially available that could allow for tuning of thermomechanical properties, potlifes, activation rates, and irradiation wavelengths. Herein, 14 catalysts and 8 photosensitizers are surveyed for the photoROMP of DCPD and the structure–activity relationships of the catalysts examined. Properties relevant to stereolithography additive manufacturing (SLA AM)─potlife, irradiation dose required to gel, conversion─are characterized to develop catalyst and photosensitizer libraries to inform development of SLA AM resin systems. Two optimized catalyst/photosensitizer systems are demonstrated in the rapid SLA printing of complex, multidimensional pDCPD structures with microscale features under ambient conditions.

Review on Computer-Aided Drug Design (CADD) Technique in Drug Discovery Researches and Solvent-Free Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones/Thiones Catalyzed by Camphor Sulfonic Acid

Combined with various computational and theoretical approaches, computer-aided drug design (CADD) is one of the contemporary approaches to drug discovery. Furthermore, this study briefly assesses the literature on computer-assisted drug design (CADD) techniques used in drug discovery research. An environmentally friendly synthetic route was developed for the convenient Biginelli synthesis of 3,4-dihydropyridine-2-(1H)-ones/thiones when no solvents are involved in the reaction using aromatic derivatives, urea/thiourea, and ethyl/methyl acetoacetate as catalysts in combination with camphor sulfonic acid (CSA). All reactions proceeded rapidly, and good product yields were obtained. Green synthesis in this study has many advantages over conventional synthesis, including a clean and environmentally friendly synthesis, easy operation, the elimination of hazardous organic solvents, a purification step free of chromatography, and the use of a non-corrosive and non-volatile catalyst. Furthermore, the method can be applied to single-tank reactions in a solvent-free environment.

Ru‐catalyzed Formation of Thiosilanes and Selenosilanes using Dichalcogenides as a User‐Friendly Alternative to Thiols and Selenols

AbstractA ruthenium‐catalyzed reaction for the selective transformation of disulfides (and diselenides) into their silyl (and germyl) counterparts has been developed, as the first example of a thiol/thiolate‐free protocol. Our strategy employs commercially available ruthenium dodecacarbonyl as the catalyst in combination with user‐friendly hydrosilanes (and hydrogermanes) and odorless dichalcogenides (S, Se). Further derivatization of heteroaryl halides into unsymmetrical sulfides demonstrated the synthetic potential of the obtained silylthioethers.

Controlling the Enantioselectivity in an Adaptable Ligand by Biomimetic Intramolecular Interlocking.

For the preparation of chiral drugs, both stereochemically stable and flexible catalysts in combination with chiral auxiliaries can be used. Here, chiral induction plays an important role in generating an enantiomerically pure catalyst. We demonstrate a successful approach to the spontaneous deracemization of tropos ligands for asymmetric catalysis. Three different constitutional isomers of a bisphosphinite ligand decorated with l-valine moieties (interaction units) linked to the flexible biphenyl system by a phenylene bridge for inducing a chiral switch were prepared. The substitution pattern's influence on the attached intermolecular recognition sites was systematically investigated. We can show that biomimetic intramolecular hydrogen bonding leads to a pronounced diastereoselective enrichment of one of the ligand stereoisomers. As a result, in the asymmetric Rh-catalyzed hydrogenation of prochiral olefins using these ligands, enantiomeric ratios of up to 95.8:4.2 (S) were obtained. Of particular note is the inversion of enantioselectivity relative to the previously reported BIBIPHOS-Rh catalyst due to the altered orientation of the biphenyl moiety from (Rax) to (Sax). The enantioselectivities achieved by appropriate intramolecular interlocking are remarkable for a tropos ligand/catalyst. The strategy presented here represents a powerful approach for the spontaneous alignment of tropos ligands, yielding high enantioselectivities in asymmetric catalysis.

Highly enantioselective vinylogous aldol reaction of dioxinone-derived silyl diene by combined Lewis acid catalyst

Highly enantioselective vinylogous aldol reaction of dioxinone-derived silyl diene by combined Lewis acid catalyst

Promoted degradation of ofloxacin by ozone integrated with Fenton-like process using iron-containing waste mineral enriched by magnetic composite as heterogeneous catalyst

In this study, a heterogeneous catalyst derived from iron-containing waste mineral was enriched by magnetic composite (Fe3+/Fe2+) at modification ratio of 5 % for the highest mineralization of ofloxacin (OFL) by ozone/Fenton system. A comparative study between O3, perozone (H2O2) and O3/Fenton systems in mineralization of ofloxacin (OFL) under various solution pH, H2O2 dosages, initial OFL concentrations and catalyst (MFS-5) dosages was performed. Adding Fenton reagent (H2O2/MFS-5) into ozonation system gave the highest OFL removal efficiency of 70 % at optimal operational conditions of pH 9, catalyst dosage of 1.5 g/L, H2O2 dosage of 100 mg/L with initial OFL concentration of 100 mg/L due to synergistic effect of O3 and Fenton reagent. The catalyst's properties were evaluated through BET, SEM image, EDS and mapping data, FTIR and XRD. The main mineralization mechanism of OFL was through hydroxyl radicals (⁎OH) which were formed during ozonation process because FeO, Fe3O4 and SiO2 in the MFS-5's constituent accelerated decomposition of O3 and promoted reaction rate with H2O2. The catalyst exhibited a good reusability and stability after five consecutive runs with negligible change in mineralization efficiency of OFL and a very low leached iron amount into solution. Besides, there was an efficient improvement of biodegradability of real pharmaceutical wastewater after treatment by O3/Fenton with 71 % and 62 % removal of COD and TOC, respectively. These findings indicated utilizing magnetic-modified waste iron mineral as heterogeneous catalyst in combination with H2O2 and O3 achieved high efficiency and feasibility in removal of OFL antibiotic from real pharmaceutical wastewater.

Enantioselective C–H Functionalization Using High-Valent Group 9 Metal Catalysts

Abstract Group 9 transition metals with a cyclopentadienyl-type ligand are highly reactive catalysts for directed C–H functionalization reactions. In this review, we summarize our recent work on the development of enantioselective C–H functionalization reactions using achiral Rh(III) or Co(III) catalysts in combination with an external chiral source such as chiral sulfonates, a Lewis base, or carboxylic acids.

Copper- and Chiral Nitroxide-Catalyzed Oxidative Kinetic Resolution of Axially Chiral N-Arylpyrroles.

A readily prepared C2-symmetric, α-hydrogen-substituted chiral hydroxylamine serves as a precatalyst to generate a chiral nitroxide in situ. This chiral nitroxide catalyst in combination with a copper co-catalyst functions as an oxidant for an unprecedented enantioselective oxidative kinetic resolution (OKR) of racemic axially chiral N-arylpyrrole alcohols using atmospheric oxygen as an environmentally friendly terminal oxidant. The OKR process provides the axially chiral N-arylpyrroles in er up to 3.5:96.5 and with s factors up to 24.

MOF-Derived Fe-Zn-N-C Catalysts for Precious Metal Free Cathodes Showing High Performance in Anion-Exchange Membrane Fuel Cells

Hydrogen technologies such as low-temperature fuel cells are, besides batteries, the most promising technologies for mobility and transport applications. Currently, Proton Exchange Membrane Fuel Cells (PEMFCs) are, in terms of low-temperature fuel cells, the state-of-the-art technology achieving high power densities and reasonable stabilities. With the recent development and increasing availability of stable and performant hydroxide conductive ionomers, Anion Exchange Membrane Fuel Cells (AEMFCs) have gained increasing interest in recent years as they combine the advantages of PEMFCs, like low-temperature operation and high-power density with the low component costs of alkaline fuel cells.1,2 Especially the possibility of replacing the expensive Pt-based electrocatalysts used in PEMFCs with cheaper electrocatalysts like nickel-based materials for the anode and iron-based materials for the cathode could significantly decrease the fuel cell costs.1,3,4 Although the oxygen reduction reaction (ORR) at the cathode is favored in alkaline media compared to acidic media, the ORR is still a challenging reaction in AEMFCs.5,6 Over the last decades, various materials were investigated in order to replace the expensive Pt electrocatalysts at the cathode. Among these materials, iron- and nitrogen-doped carbons (Fe-N-C) with molecular iron sites (Fe-Nx) show comparable catalytic activities to Pt and decent stabilities.7–9 Fe-N-C catalysts can be obtained by co-pyrolysis of Fe- N-, and C-sources and subsequential acid leaching. One way to achieve Fe-N-C catalysts with high dispersion of Fe-Nx sites is by using Fe-doped metal-organic frameworks (Fe-MOFs) as precursors. These combine the presence of pre-coordinated Fe-Nx motives as well as high porosity and high specific surface area.10 To produce Fe-N-C catalysts, we synthesized Fe-, and Zn-doped MOFs (Fe-Zn-MOF) as multicomponent Fe-, Zn-, N-, and C-precursors and pyrolyzed them in the presence of additional nitrogen sources at high temperatures. The resulting Fe-Zn-N-C catalysts revealed high dispersion of Fe and Zn, high specific surface areas (400-600 m2/g), and high porosity as revealed by XRD, EDX, HAADF STEM, and N2 physisorption. Depending on the pre-treatment of the Fe-Zn-MOF, the Fe content of the resulting Fe-N-C catalyst could be varied. Benefiting from the high Fe-dispersion and the high specific surface areas, the best performing Fe-Zn-N-C catalyst with high Fe content shows high activity towards the ORR in alkaline media (0.1 mol/L KOH) as demonstrated by RDE measurements featuring a high half-wave potential (0.87 V vs. RHE) and high mass activity (47 mA/mgcat) and thereby outperforming a commercial 50 wt.% Pt/C catalyst in terms of half-wave potential (0.83 V vs. RHE).To investigate the performance of the Fe-Zn-N-C catalysts in AEMFCs, membrane electrode assemblies (MEAs) were prepared with the synthesized Fe-Zn-N-C catalysts at the cathode, a commercial PtRu/C catalyst (40 wt.% Pt, 20 wt.% Ru on carbon black, AlfaAesar) at the anode, and a commercial ionomer as membrane and catalyst layer ionomer. The AEMFC with the best performing Fe-Zn-N-C catalyst revealed a high peak power density of 850 mW/cm², which is among the highest reported peak power densities for non-precious metal cathode catalysts in combination with a commercially available anion exchange ionomer.1 D. R. Dekel, J. Power Sources, 2018, 375, 158–169.2 R. O’Hayre, S.-W. Cha, W. Colella and F. B. Prinz, Fuel Cell Fundamentals, John Wiley & Sons, Inc, Hoboken, NJ, USA, 2016.3 X. Ge, A. Sumboja, D. Wuu, T. An, B. Li, F. W. T. Goh, T. S. A. Hor, Y. Zong and Z. Liu, ACS Catal., 2015, 5, 4643–4667.4 E. S. Davydova, S. Mukerjee, F. Jaouen and D. R. Dekel, ACS Catal., 2018, 8, 6665–6690.5 M. Hren, M. Božič, D. Fakin, K. S. Kleinschek and S. Gorgieva, Sustain. Energy Fuels, 2021, 5, 604–637.6 N. Ramaswamy and S. Mukerjee, Adv. Phys. Chem., 2012, 2012, 1–17.7 X. Ren, B. Liu, X. Liang, Y. Wang, Q. Lv and A. Liu, J. Electrochem. Soc., 2021, 168, 044521.8 L. Osmieri, L. Pezzolato and S. Specchia, Curr. Opin. Electrochem., 2018, 9, 240–256.9 M. M. Hossen, K. Artyushkova, P. Atanassov and A. Serov, J. Power Sources, 2018, 375, 214–221.10 C. Li, D. H. Zhao, H. L. Long and M. Li, Rare Met., 2021, 40, 2657–2689.

Ni/support-CaO bifunctional combined materials for integrated CO2 capture and reverse water-gas shift reaction: Influence of different supports

Integrated CO2 capture and utilisation (ICCU) is a promising strategy for restricting carbon emissions and achieving carbon neutrality. Bifunctional combined materials (BCMs), containing adsorbents and active catalysts, are widely applied in this process. Producing syngas via reverse water–gas shift reaction (RWGS) and integrating with Fischer-Tropsch (F-T) synthesis is an attractive and valuable CO2 utilisation route. This work investigated a series of Ni/support-CaO BCMs (supports = ZrO2, TiO2, CeO2 and Al2O3) for the integrated CO2 capture and RWGS (ICCU-RWGS) process. The Ni/support-CaO BCMs were prepared by physically mixing various metal oxide supports loaded Ni with sol–gel derived CaO. The ICCU-RWGS performance (CO2 conversion, CO yield and CO generation rate) of these BCMs followed the order during tested conditions (550–750 °C): Ni/CeO2-CaO > Ni/TiO2-CaO > Ni/ZrO2-CaO > Ni/Al2O3-CaO. A comprehensive characterisation of Ni/support materials showed that Ni/CeO2 had the characteristics of stronger basicity, optimal Ni dispersion and improved NiO reducibility, which led to the outperforming ICCU-RWGS activity over Ni/CeO2-CaO (e.g. 56.1% CO2 conversion, 2.68 mmol g−1 CO yield and ∼100% CO selectivity at 650 °C). Furthermore, the Ni/CeO2-CaO BCM showed a stable, yet, self-optimising catalytic performance during the cyclic ICCU-RWGS reaction over 20 cycles. The TEM characterisation suggested that was ascribed to the volume expansion and shrinkage of CaO in the cyclic adsorption–desorption altering the distance between the adsorbent and Ni/CeO2, resulting in an enhanced CO2 conversion during the cycle.

Prediction of Combined Sorbent and Catalyst Materials for SE-SMR, Using QSPR and Multitask Learning.

The process of sorption enhanced steam methane reforming (SE-SMR) is an emerging technology for the production of low carbon hydrogen. The development of a suitable catalytic material, as well as a CO2 adsorbent with high capture capacity, has slowed the upscaling of this process to date. In this study, to aid the development of a combined sorbent catalyst material (CSCM) for SE-SMR, a novel approach involving quantitative structure–property relationship analysis (QSPR) has been proposed. Through data-mining, two databases have been developed for the prediction of the last cycle capacity (gCO2/gsorbent) and methane conversion (%). Multitask learning (MTL) was applied for the prediction of CSCM properties. Patterns in the data of this study have also yielded further insights; colored scatter plots were able to show certain patterns in the input data, as well as suggestions on how to develop an optimal material. With the results from the actual vs predicted plots collated, raw materials and synthesis conditions were proposed that could lead to the development of a CSCM that has good performance with respect to both the last cycle capacity and the methane conversion.

Design of Au nanorods-based plasmonic catalyst in combination with nanohybrid Pd-rGO layer for boosting CO2 hydrogenation to formic acid under visible light irradiation

In recent years, research on the use of surface plasmon resonance phenomena induced by visible to near-infrared light for photocatalytic reactions has attracted much attention from the viewpoint of solar energy utilization. It has been extensively researched that the plasmon-mediated catalytic reaction can be promoted due to the injection of energetic hot electrons originating during the relaxation process of the surface plasmon resonance (SPR) into the reaction substrate molecules. In this report, we have prepared Pd/Au NRs@rGO nanocatalyst in which Au nanorods (NRs) with plasmonic properties are surrounded by a layer of reduced graphene oxide (rGO) with excellent electrical conductivity, and Pd nanoparticles (NPs) are supported on the Au NRs to efficiently transport hot electrons to the reaction substrate. The successful synthesis of the catalyst was characterized by HAADF-STEM, TEM, UV–vis, XRD, XAFS, and ICP analysis. The applicability of the prepared catalyst was tested in the photocatalytic reduction of CO2 to formic acid (FA) reaction under visible light irradiation. A photocatalytic FA yield of 1.7 μmol was obtained in 24 h, which was 2.7-fold higher than in dark reaction conditions. The SPR enhancement of Pd/Au NRs in combination with rGO in Pd/Au NRs@rGO catalyst led to the superior product yield of FA under visible light irradiation and room temperature conditions.

Controllable transformation of sheet-like CoMo-hydro(oxide) and phosphide arrays on nickel foam as efficient catalysts for alkali water splitting and Zn–H2O cell

Design and synthesis of cost-effective electrocatalysts with remarkable activity and stability is highly desirable for renewable energy devices. Herein, we have successfully constructed sheet-like CoMoO4–Co(OH)2 and CoMoP–CoP arrays on nickel foam (NF) through chemical etching ZIF-67 arrays and phosphorization in sequence. Series CoMoO4–Co(OH)2/NF as anode and CoMoP–CoP/NF as cathode showed excellent electrocatalytic activity and stability in alkali water splitting, where the combined catalysts only need 1.67 V cell voltage to drive 10 mA cm−2 and obtain robust high current stability at 500 mA cm−2 for 110 h with almost no attenuation. In addition, using CoMoP–CoP/NF as the cathode of a Zn–H2O cell can provide a power density of 11.5 mW cm−2 and a stable 170 h for simultaneous H2 and electricity generation. The excellent performance of the system is attributed to the unique sheet-like array morphology of combined catalysts providing large surface area and rich pore structure conducive to electrolyte diffusion and gas emission, as well as the synergies between the different components providing more catalytic active sites.

In-service insights into flue gas oxidation catalyst for natural gas-fueled power generation applications

A natural gas-fueled power generation application is sustainable to the degree that its flue gas oxidation catalyst operates with robust high performance. This study of an industrial catalyst revealed distinct application features, namely: (i) combined cycle operation generated a low contaminant accumulation that strongly correlated with performance reliability, and (ii) simple cycle operation generated a high contaminant accumulation that weakly correlated with performance reliability. Operation type also determined the influences of catalyst design on performance reliability. Combined cycle operation favored catalysts with sufficient PGM loading and high cell density substrate, while simple cycle operation favored catalysts with higher PGM loading and low cell density substrate.

REGULARITIES OF HYDROGEN GENERATION BY HYDROLYSIS OF SODIUM BOROHYDRIDE ON IMMOBILIZED PLATINUM CATALYSTS

Sodium borohydride hydrolysisis one of the most productive hydrogengeneration methods, which can be used, inparticular, to power fuel cells with a hydrogenanode. In alkaline solutions, the interaction of NaBH4 with water practically does not occur, which makes it possible to store such solutions for a longtime. However, in the presence of catalysts, the borohydride hydrolysis reaction actively proceeds at room temperature with the formation of hydrogenand sodium metaborate. More than 300 homogeneous and heterogeneous catalysts for the hydrolysis of sodium borohydride are known, among which the most active metal catalysts are nanodispersed rhodium, ruthenium, and platinum immobilized on various substrates. The activity of such catalysts depends on the conditions of the reduction and immobilization of metals, the nature of used precursors, the amount of active phase of the catalyst, and the type of substrate. In this work, platinum catalysts immobilized on several substrates are developed, and the regularities of hydrolysis of sodium borohydride in alkaline solution when using such catalysts in flowing flat and cylindrical reactors are investigated. Using various methods, platinum was deposited on carbon black and carbon cloth, onactivated granular carbon, on titanium crumb, and on synthetic cordierite of honey combstructure with surface, previously modified by alumina. It is shown that nanodisperse platinum catalysts immobilized on carbon black and carbon cloth and especially on synthetic cordierite of cellular structure with surface previously modified by Al2O3 layer are active and reliable. The average rate of hydrogen evolution during hydrolysis of NaBH4 on such catalysts increases with increasing flow rate of its solution through the reactor, but the degree of conversion of sodium borohydride decreases due to the reduced duration of contact of the solution with the catalyst. Nanodisperse platinum catalysts on surface-modified cordierite provide a highandstable rate of hydrogengeneration with moderate heating of NaBH4 solution (60±5°C). The use of hydrogen generators with such catalysts in combination with fuel cell batteries is promising for the creation of autonomous powers ources.