Platinum-containing Catalysts Research Articles

Exploring the Potential of Bimetallic PtPd/C Cathode Catalysts to Enhance the Performance of PEM Fuel Cells.

Bimetallic platinum-containing catalysts are deemed promising for electrolyzers and proton-exchange membrane fuel cells (PEMFCs). A significant number of laboratory studies and commercial offers are related to PtNi/C and PtCo/C electrocatalysts. The behavior of PtPd/C catalysts has been studied much less, although palladium itself is the metal closest to platinum in its properties. Using a series of characterization methods, this paper presents a comparative study of structural characteristics of the commercial PtPd/C catalysts containing 38% wt. of precious metals and the well-known HiSpec4000 Pt/C catalyst. The electrochemical behavior of the catalysts was studied both in a three-electrode electrochemical cell and in the membrane electrode assemblies (MEAs) of hydrogen-air PEMFCs. Both PtPd/C samples demonstrated higher values of the electrochemically active surface area, as well as greater specific and mass activity in the oxygen reduction reaction in comparison with conventional Pt/C, while not being inferior to the latter in durability. The MEA based on the best of the PtPd/C catalysts also exhibited higher performance in single tests and long-term durability testing. The results of this study conducted indicate the prospects of using bimetallic PtPd/C materials for cathode catalysts in PEMFCs.

CONVERSİON OF n-HEXANE OVER CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE

The isomerization process is becoming increasingly important in the modern petroleum refining context due to the limitations on the content of benzene, aromatic compounds, and olefins in gasoline. Isomerization is an effective and profitable process for octane enhancement of gasoline unlike other octane increasing processes. Due to the low sulfur and benzene content, the isomerate can be used as an ideal blending gasoline component. Therefore, the isomerization process has a great importance in petroleum refineries to increase the fuel octane number. This article aimed to study the conversion process of normal hexane over palladium and platinum containing catalysts on the base of sulfated zirconium dioxide. It has been determined that due to their high-performance characteristics, catalytic systems based on sulfated zirconium dioxide can be considered the most promising for isomerization of normal alkanes. Moreover, comparison of palladium-containing catalysts based on sulfated zirconium dioxide with platinum-containing catalysts based on sulfated zirconium dioxide showed that palladium sulfated zirconia catalysts have high catalytic performance in the isomerization of normal hexane. Keywords: alkanes, catalyst, platinum, palladium, isomerization, temperature, sulfated zirconium dioxide. .

Methanol Decomposition to Synthesis Gas over Supported Platinum-Containing Catalysts

Methanol Decomposition to Synthesis Gas over Supported Platinum-Containing Catalysts

Influence of the Carbon Support on the Structural–Morphological Parameters and Electrochemical Properties of Platinum-Containing Catalysts for Fuel-Cell Cathode with a Proton-Exchange Membrane

Influence of the Carbon Support on the Structural–Morphological Parameters and Electrochemical Properties of Platinum-Containing Catalysts for Fuel-Cell Cathode with a Proton-Exchange Membrane

CATALYSTS OF THE ISOMERIZATION PROCESS OF n-HEXANE

Information on the isomerization of n-hexane is systematized. It has been shown that the process of isomerization of n-alkanes is a priority issue in solving the problems of improving the quality of modern automobile gasolines and their compliance with environmental requirements. The use of low-octane fractions as raw materials determines the high efficiency of the process in addition to the production of high-value isomerizate. The obtained isomerizate meets all the requirements for motor fuels: high impact resistance, easy volatility, absence of benzene, olefins and sulfur. The article presents thermodynamic data, provides general information about modern catalytic systems used in the isomerization of n-alkanes, and shows their mechanisms of action. Comparative data on Friedel-Crafts catalyst, chlorinated alumina, zeolites, sulfated and tungsten-containing zirconium, and heteropolyacids are summarized. In the process of isomerization of the pentane-hexane fraction, platinum-containing catalysts based on chlorinated aluminum oxide, zeolites and sulfated zirconium dioxide are used in industry. SO4/ZrO2-based catalysts can be considered the most promising due to their high performance indicators. The current work is mainly focused on the systematic study of the physico-chemical regularities of the formation and isomerization activity of catalysts based on anion-modified oxides, depending on their composition and preparation conditions. Keywords: n-hexane, isomerization, thermodynamics, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, catalytic systems.

Development of Palladium and Platinum Decorated Granulated Carbon Nanocomposites for Catalytic Chlorate Elimination.

Granulated carbon nanotube-supported palladium and platinum-containing catalysts were developed. By using these, remarkable catalytic activity was achieved in chlorate ion hydrogenation. Nitrogen-doped bamboo-like carbon nanotubes (N-BCNTs) loaded gel beads were prepared by using Ca2+, Ni2+ or Fe3+ ions as precursors for cross-linking of sodium alginate. The gel beads were carbonized at 800 °C, and these granulated carbon nanocomposites (GCNC) were used as supports to prepare palladium and platinum-containing catalysts. All in all, three catalysts were developed and, in each case, >99 n/n% chlorate conversion was reached in the aqueous phase by using the Pd-Pt containing GCNCs, moreover, these systems retained their catalytic activity even after repeated use.

Effect of Support on Catalytic Properties of Platinum-Containing Catalysts in Hydrogenation of a Biphenyl–Diphenylmethane Eutectic Mixture

Effect of Support on Catalytic Properties of Platinum-Containing Catalysts in Hydrogenation of a Biphenyl–Diphenylmethane Eutectic Mixture

Development of Nickel- and Magnetite-Promoted Carbonized Cellulose Bead-Supported Bimetallic Pd-Pt Catalysts for Hydrogenation of Chlorate Ions in Aqueous Solution.

Cellulose grains were carbonized and applied as catalyst supports for nickel- and magnetite-promoted bimetallic palladium- and platinum-containing catalysts. The bimetallic spherical aggregates of Pd and Pt particles were created to enhance the synergistic effect among the precious metals during catalytic processes. As a first step, the cellulose bead-based supports were impregnated by nitrate salts of nickel and iron and carbonized at 973 K. After this step, the nickel was in an elemental state, while the iron was in a magnetite form in the corresponding supports. Then, Pd and Pt particles were deposited onto the supports and the catalyst surface; precious metal nanoparticles (10–20 nm) were clustered inside spherical aggregated particles 500–600 nm in size. The final bimetallic catalysts (i.e., Pd–Pt/CCB, Pd–Pt/Ni–CCB, and Pd–Pt/Fe3O4–CCB) were tested in hydrogenation of chlorate ions in the aqueous phase. For the nickel-promoted Pd–Pt catalyst, a >99% chlorate conversion was reached after 45 min at 80 °C. In contrast, the magnetite-promoted sample reached an 84.6% chlorate conversion after 3 h. Reuse tests were also carried out with the catalysts, and in the case of Pd–Pt/Ni–CCB after five cycles, the catalytic activity only decreased by ~7% which proves the stability of the system.

Selective Hydration of Furfurol in the Presence of Platinum-Containing Catalysts

Selective Hydration of Furfurol in the Presence of Platinum-Containing Catalysts

EFFECT OF POLYVINYLPYRROLIDONE ON THE SYNTHESIS AND CATALYTIC PROPERTIES OF PLATINUM-CONTAINING OXYGEN ELECTROREDUCTION CATALYSTS

Results of the work on the synthesis of highly effective nanocomposite platinum-containing oxygen reduction electrocatalysts for hydrogen-oxygen fuel cells are presented and ways of increasing their activity are considered. Fuel cells (FCs) represent the most promising renewable and environmentally friendly energy sources that can operate at low temperatures with high efficiency and with low or zero levels of hazardous waste. The main problem of fuel cells is that the oxygen reduction reaction is slowed down in relation to the hydrogen oxidation reaction, which leads to an increase in the overvoltage at the cathode and, as a result, to a decrease in the productivity of FCs. To solve this problem, the new methods are being developed for the synthesis of highly efficient platinum electrocatalysts, which currently have the best performance, since platinum has the highest specific catalytic activity among other materials used in low temperature FCs. The purpose of this work is to determine the optimal composition of reaction mixture and conditions for the preparation of a platinum based catalyst for oxygen electroreduction where Vulcan XC-72 nanodispersed carbon black is used as a carrier. We have worked out 6 methods for preparing Pt (40 %)/XC-72 catalysts. To evaluate the activity of the prepared catalysts and to determine the kinetic parameters of the oxygen reduction on them, cathodic stationary polarization curves were recorded in a 0.5 M H2SO4 solution on a floating gas diffusion electrode superficially modified by the catalysts. For preparation of all electrocatalysts we are used 3.6 ml of a hexachloroplatinic acid (H2PtCl6) solution, containing 18.8 mg Pt/ml, 100 ml of ethylene glycol or its mixture with deionized water (3 : 1) and 100 mg of Vulcan XC-72 carbon black, previously oxidized in HNO3 solution. 1 M NaOH or KOH solutions were used to create the necessary medium (pH = 11). Some Pt(40 %)/XC-72 electrocatalysts were prepared when additions of polyvinylpyrrolidone (PVP) (100 mg or 300 mg) and/or 60 ml of formaldehyde were introduced into reaction mixture. Temperature during syntheses was in the range 75 - 160 °C. It was shown that reducing the synthesis temperature from 160 to 75 °C and introduction of PVP together with formaldehyde into reaction mixture had a positive effect on the activity of obtained nanocomposite platinum-containing catalysts Pt(40 %)/XC-72 for oxygen electroreduction.The sizes of the obtained platinum clusters on the surface of carbon black nanoparticles were in the range of 1.7 - 5.7 nm, and under optimal synthesis conditions they were evenly and densely distributed on the surface of the carbon carrier. The obtained kinetic characteristics of oxygen electroreduction on the studied catalysts indicate that the mechanism of this process depended on both the current density and the method of catalyst synthesis.

A New Catalyst Modified with Nanosized Molybdenum Carbides for the Hydroisomerization of n-Alkanes and Its Catalytic Properties in the Hydroisomerization of Diesel Fractions, Part II: Preparation of Bifunctional Hydroisomerization Catalysts

The aim of this work is to develop a new hydroisomerization catalyst based on molybdenum carbides that is resistant to the influence of sulfur compounds and applicable for the synthesis of low-pour-point diesel fuels that are similar in parameters to the fuel synthesized using platinum-containing catalysts. In the first part of the work, supports with different porous structures and acidities (Beta, ZSM-5, ZSM-12, and SAPO-31) are synthesized and studied. In the second part of the work, bifunctional catalysts prepared by modifying these supports with nanosized molybdenum carbides are studied. All samples contain the same amount of Mo2C (10% in terms of the equivalent amount of MoO3). The catalysts are tested using a model isomerization reaction of n-decane. The catalyst based on silicoaluminophosphate ATO (SAPO-31) proves to be the most effective one. In order to optimize its composition, larger batches of samples with different Mo2C contents (5, 7 and 10% in terms of the equivalent amount of MoO3) are prepared. The catalytic properties are studied using the hydroisomerization of actual diesel fractions. The optimum content of Mo2C (7 wt %) in the bifunctional catalyst is determined.

A New n-Alkane Hydroisomerization Catalyst Modified with Nanosized Molybdenum Carbides and Its Catalytic Properties in Diesel Fraction Hydroisomerization. Part III: Comparison of the Catalytic Properties of Bifunctional SAPO-31 and SAPO-11 Based Catalysts

Part III of this work continues the study of the catalytic properties of new molybdenum carbide based hydroisomerization catalysts, which are resistant to sulfur compounds and allow the synthesis of waxy diesel fuels with the same quality characteristics as those of platinum-containing catalysts. The catalytic properties of such bifunctional catalysts as 7%Mo2C/SAPO-31 (LCCH-2) and 7%Mo2C/SAPO-11 (LCCH-2-2) in diesel fraction hydroisomerization in the temperature range of 320–400°C are compared. It is shown that LCCH-2 ensures a higher yield of the hydroisomerized diesel fraction with a lower freezing point as compared to LCCH-2-2 at temperatures above 320°C. The ratio between mono- and di-isomers in reaction products is analyzed. It is concluded that SAPO-31 based catalyst is more selective to the formation of terminal monosubstituted alkanes than SAPO-11 based catalyst. The resistance of both catalysts to deactivation with coke deposits (tests over 100 h at 320 and 360°C in hydroisomerization) is studied. It is established that LCCH-2-2 is less resistant to deactivation than LCCH-2. These findings are due to differences in acidity, the degree of uniformity in the distribution of acidic hydrogenating/dehydrogenating sites in the catalysts, and the structural type of their acidic supports.

Comparative Study of Special Features of the Oxygen Reaction (Molecular Oxygen Ionization and Evolution) in Aqueous and Nonaqueous Electrolyte Solutions (a Review)

Studies of the oxygen reaction, including the oxygen ionization and evolution processes occurring at typical electrode materials in aqueous and nonaqueous electrolytes, are analyzed. A connection between the problematics of the oxygen electrode reaction in nonaqueous media and the developing of novel batteries, in the first place, Li–O2 batteries, is emphasized. Unlike aqueous solutions, the oxygen reduction in aprotic electrolytes was shown to occur without breaking of the O–O bond; it is accompanied by formation of poorly soluble product of two-electron reaction (Li2O2) in the pores of positive electrode. The effect of the solvent donor number and the anion composition on the oxygen reduction mechanism and the lithium peroxide deposit structure is described. A marked reduction of the Li2O2 oxidation overvoltage when passing from carbonaceous materials to platinum-containing catalysts in the positive electrode is elucidated; in the latter case, the effect of electrocatalyst type upon the Li2O2 formation reaction is somewhat reduced. The elucidation of the contribution of processes occurring at the free and lithium-peroxide-covered electrode surface during the oxygen reaction for wide variety of active materials is formulated as the main basic problem of the future research.

A new n-alkane hydroisomerization catalyst modified with nanosized molybdenum carbides and its catalytic properties in diesel fraction hydroisomerization. I. Synthesis and physicochemical properties of different acidic supports for hydroisomerization catalysts

Hydroisomerization catalysts based on nanosized molybdenum carbides are developed. Such catalysts are resistant to sulfur compounds and can be used for the synthesis of waxy diesel fuels with the same characteristics as on platinum-containing catalysts. In the first part of this work, acidic supports with different types of porous structure and concentrations and strengths of Bronsted acidic sites (e.g., silicoaluminophosphate SAPO-31, zeolite ZSM-12, modified zeolite Beta, and desiliconized zeolite ZSM-5) are synthesized for a new type of catalysts. Their physicochemical properties are studied by means of adsorption, temperature- programmed desorption of ammonia (TPD-NH3), nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM).

New Catalyst Modified with Nanosize Molybdenum Carbides for Hydroisomerization of n-Alkane, its Catalytic Behavior in the Process of Hydroisomerization of Diesel Fractions. Part 3. Comparison of Catalytic Properties of Bifunctional Catalysts Based on SAPO

Part 3 of the studies dealt with catalytic properties of the new catalysts based on molylbdenum carbides, resistant to sulfur compounds and providing manufacturing of low pour point diesel fuel with the quality indices identical to those obtained with platinum-containing catalysts. Catalytic properties of bifunctional catalysts 7%Mo2C/SAPO-31 (LCCH-2) and 7%Mo2C/SAPO-11 (LCCH-2-2) for hydroisomerization of diesel fractions were compared at the temperature range between 320 and 400 °C. It was shown that at above 320 °C the catalyst LCCH-2, against LCCCH-2-2, provided the formation of the hydroisomerized diesel fraction at a higher yield and freezing at a lower temperature. Inspection of the data on the ratio of total quantities of monomers and diisomers in the reaction products led to conclude that the former catalyst is more selective than the latter to the formation of terminal monosubstituted alkanes. Studies of the stability of both catalysts to deactivation with coke deposits (100 hour testing at 320 and 360 °C during hydroisomerization) revealed that LCCH-2-2 is less stable to deactivation than LCCH-2. The observed regularities were accounted for by differences in the acidities, degree of homogeneity of distribution of acid and hydrating-dehydrating centers through the catalysts under study, and types of structures of the acid support.

Coordination compounds as the precursors for preparation of nanosized platinum or platinum-containing mixed-metal catalysts of oxygen reduction reaction

Nanosized mixed-metal platinum-iron, platinum-anganese and platinum-nickel catalysts supported on highly dispersed carbon black are synthesized by using the corresponding metal complexes with the atomic metal ratio of 1:1. The obtained catalysts are characterized by X-ray phase diffraction and scattering analysis, electron dispersion analysis, scanning and transmission electron microscopy. Thin film rotating disk electrode technique was used to study kinetic parameters of the oxygen reduction reaction at these catalysts. It has been demonstrated that electrochemical activity of the prepared catalysts is comparable to that of a commercial E-Tek platinum catalyst. The membrane electrode assembly (MEA) with the synthesized platinum-iron catalyst was tested in a laboratory hydrogen-air fuel cell setup at room temperature. It was shown that the power performance of this MEA was twice better than that of a MEA on the base of a commercial Pt/C E-Tek catalyst.

Preparation of platinum-containing hydrogenation catalysts supported on thermally reduced graphite oxide

Graphene-like materials with an atomic ratio of C/O > 40 have been prepared by calcination of graphite oxide (C/O = 1.46) in an inert atmosphere. Platinum nanoparticles (average size of ~2.0 nm) have been deposited onto the surface of the materials from an aqueous solution of H2PtCl6 · xH2O in the presence of pyridine. These particles catalyze the liquid-phase hydrogenation of PhNO2 to PhNH2 and that of the double bonds in 1-decene and styrene. As a support, the defect-containing graphene-like material prepared by calcination of graphite oxide at 1000–1050°C for 3 h has certain advantages over graphite oxide reduced by chemical means or by short-term heating. This material and catalysts supported on it can be formed as “carbon paper” by vacuum filtration.

Properties of platinum-containing glass-fiber catalysts in the SO2 oxidation reaction

SO2 oxidation catalysts containing small amounts (0.01–0.03 mass%) of platinum at the zirconia-promoted silica glass fibers (Pt-GFCs) demonstrate relatively high activity at moderate temperatures (below 400 °C) and the appropriate thermal stability (up to 700 °C). The catalytic activity of Pt-GFC in the SO2 oxidation reaction is provided by the small (< 1 nm) partially charged platinum clusters, while platinum in a form of large metal particles is practically inactive. Pt-GFCs have the high (up to ~20 mass%) sorption capacity with respect to SO2. Such sorption occurs via the interaction of SO2 with oxygen, either present in the gaseous reaction mixture or pre-adsorbed in the fresh GFC structure, with the possible formation of the intermediate sulfates in the glass bulk of the catalyst. Besides, Pt-GFC may effectively oxidize CO in the presence of significant amounts of sulfur dioxide.

Coordination Compounds as the Precursors for Preparation of Nanosized Platinum or Platinum-Containing Mixed-Metal Catalysts of Oxygen Reduction Reaction

Coordination Compounds as the Precursors for Preparation of Nanosized Platinum or Platinum-Containing Mixed-Metal Catalysts of Oxygen Reduction Reaction

Synthesis and characterization of the Pt/Al2O3 systems modified with group III (Ga) and Group IV (Ge, Ti, and Zr) elements in the combined conversion of propane and n-Heptane

Under the conditions of a joint reaction of propane and n-heptane at temperatures of 460–520°C and a pressure of 0.35 MPa, the conversion of propane and the concentration of C7+ aromatization products on platinum-containing catalysts modified by Group III (Ga) and Group IV (Ge, Ti, and Zr) elements were higher than those on an unmodified Pt/Al2O3 sample. This is explained by a change in the aprotic acidity of the catalysts as a result of the support modification. The sample with the addition of gallium was most active. A plausible reason for this is the conversion of hydrocarbons at active sites that consist of Pt and Ga, which were formed upon catalyst activation. It is believed that gallium adjacent to platinum in an ionic form on the support surface acts as an aprotic acid site.