Platinum-alumina Catalysts Research Articles

Catalytic properties of the platinum catalyst supported on alumina modified by oxalic acid in n-heptane reforming

Structural modification of alumina was carried out by the decomposition of the products of the reaction of aluminum hydroxide with the organic acid used simultaneously as a peptizer and a “burnable” additive. The modification changes the acidity of the support surface and induces the formation of pentacoordinate Al3+ cations interacting with platinum, which increases the fraction of platinum atoms with electron deficiency. The alumina-platinum catalyst based on the support treated with oxalic acid shows an enhanced selectivity to aromatization in n-heptane reforming.

Joint Conversion of Methane with Pentane on Alumina–Platinum Catalysts Modified with Zirconium Oxide under Nonoxidizing Conditions

The physicochemical properties of alumina–platinum catalysts with supports prepared by mixing aluminum and zirconium hydroxides have been studied. The chemisorption and nonoxidative conversion of methane in the presence of the above systems have been investigated. The effect of the zirconium content on the activity and selectivity of the conversion of chemisorbed CH4 and n-C5H12 into aromatic hydrocarbons has been established.

Synthesis of layered magnesium-aluminum hydroxide on the γ-Al2O3 surface for modifying the properties of supported platinum catalysts

Layered magnesium-aluminum hydroxides of hydrotalcite-like structure were synthesized on the surface of γ-Al2O3. The synthesis was performed via the interaction of aluminum and magnesium hydroxides and carbonate ions in the pores of alumina support. Novelty of the approach was that the synthesis involved the boehmite phase AlO(OH) that formed directly on the surface of γ-Al2O3 under hydrothermal conditions. This approach provides fixation of the forming layered phase on the surface of initial support and retains textural parameters of the support. The formation of a layered structure on the γ-Al2O3 surface was confirmed by XRD analysis and electron microscopy studies. Investigation of the H2[PtCl6] anchoring on γ-Al2O3 with supported magnesium-aluminum hydroxide by UV–vis DRS, 195Pt NMR and HRTEM showed that platinum was adsorbed on the surface as chloride forms of the complexes with a low degree of hydrolysis even at a low metal content. Catalytic properties of the synthesized supported platinum catalysts were examined in a model reaction of propane dehydrogenation. In comparison with the alumina-platinum catalyst, the modified sample showed a better stability at a somewhat higher yield of propylene because the formation of heavy products was suppressed.

New Data on the Ability of Alumina–Platinum Systems to Catalyze the Methane Aromatization Reaction under Nonoxidizing Conditions

The state and size of the metal on the surface of aluminum oxide and the acidic properties of the support depending on the concentration of supported platinum were studied in this work. The effect of the Pt content of the alumina–platinum catalyst on the activation (chemisorption) of methane was investigated, and the composition of hydrocarbon fragments formed in this case was calculated. The sample most active in a reaction of the joint conversion of methane with n-pentane, which was performed for the production of aromatic hydrocarbons under nonoxidizing conditions, was established. The effect of the temperature of n-pentane supply to the reaction atmosphere was studied for the 0.6%Pt/Al2O3 catalyst. The degree of enrichment of the resulting aromatic hydrocarbons and the quantity of incorporated methane activated on the catalyst surface were determined with the use of isotope mass spectrometry.

Tritium oxidation test by platinum-alumina catalyst under moisture and hydrocarbons atmosphere

To design a detritiation system (DS) applicable to a fire event, it is important to investigate influence of moisture and hydrocarbons produced by combustion of cables in fire on tritium oxidation efficiency of a catalytic reactor. In our experiments, when we assumed that tritium release in a simulated room in the following scenarios as fire situation, (I) tritium only; (II) tritium and excess moisture; (III) tritium and excess hydrocarbons, we conducted demonstration test of tritium oxidation using by DS consist of a catalytic reactor packed with platinum-alumina catalyst and a dryer with molecular sieves. We investigated the detritiation behavior and determined the volume of catalyst to satisfy requirement of tritium oxidation efficiency of a catalytic reactor packed with the catalyst. The tritium concentration theoretically decreased by DS since the tritium oxidation efficiency kept high under the conditions of three scenarios. Our results showed that the concentration of hydrogen in air and temperature of catalyst had an influence on the tritium oxidation efficiency of the catalytic reactor. We determined the worst scenario for tritium oxidation and evaluated the amount of catalyst to meet the requirement of the tritium oxidation efficiency.

A comparative parametric study of a catalytic plate methane reformer coated with segmented and continuous layers of combustion catalyst for hydrogen production

Abstract A parametric comparison study is carried out between segmented and conventional continuous layer configurations of the coated combustion-catalyst to investigate their influence on the performance of methane steam reforming (MSR) for hydrogen production in a catalytic plate reactor (CPR). MSR is simulated on one side of a thin plate over a continuous layer of nickel-alumina catalyst by implementing an experimentally validated surface microkinetic model. Required thermal energy for the MSR reaction is supplied by simulating catalytic methane combustion (CMC) on the opposite side of the plate over segmented and continuous layer of a platinum-alumina catalyst by implementing power law rate model. The simulation results of both coating configurations of the combustion-catalyst are compared using the following parameters: (1) co-flow and counter-flow modes between CMC and MSR, (2) gas hourly space velocity and (3) reforming-catalyst thickness. The study explains why CPR designed with the segmented combustion-catalyst and co-flow mode shows superior performance not only in terms of high hydrogen production but also in terms of minimizing the maximum reactor plate temperature and thermal hot-spots. The study shows that the segmented coating requires 7% to 8% less combustion-side feed flow and 70% less combustion-catalyst to produce the required flow of hydrogen (29.80 mol/h) on the reforming-side to feed a 1 kW fuel-cell compared to the conventional continuous coating of the combustion-catalyst.

Mechanism of the reductive dehydration of ethanol into C3+ alkanes over the commercial alumina—platinum catalyst AP-64

The mechanism of the reductive dehydration of ethanol (RDE) into C3+ alkanes over the commercial alumina—platinum catalyst AP-64 has been investigated. The catalyst pre-reduction time has an effect on the conversion of ethanol and on that of ethylene, a possible intermediate compound in the RDE reaction. Over the catalyst reduced for 12 h, ethanol turns into a C3-C12 alkane fraction and ethylene turns into a C3-C12 olefin fraction, whose yields are 39.0 and 31.4%, respectively. Energetic parameters of ethanol chemisorption and conversion on a Pt6Al4 cluster have been determined by the density functional theory method using the PRIRODA 13 program. Ethanol dehydration into ethylene proceeds via the successive breaking of C-H and C-O bonds, and the rate-determining step of the process depends on the atom (Pt or Al) to which the OH group of the alcohol is coordinated. Hydroxyl group transfer from the Pt atom to the nearest Al atom is energetically favorable here. It is hypothesized that the main role of the metal-containing cluster is donation of chemisorbed ethylene to the nearest acid sites, on which the ethylene oligomerizes into a C3-C10 hydrocarbon fraction.

Влияние добавки инертных газов на глубокое окисление метана и бутана на алюмоплатиновом катализаторе

Влияние добавки инертных газов на глубокое окисление метана и бутана на алюмоплатиновом катализаторе

Total oxidation of propane in vanadia-promoted platinum-alumina catalysts: Influence of the order of impregnation

Differently prepared vanadium promoted Pt/alumina catalysts have been prepared, characterized and tested for propane total oxidation. V-promoted Pt/Al2O3 catalysts have shown remarkably higher catalytic activity than V-free Pt/Al2O3 catalyst. Among V-promoted Pt catalysts that prepared by coimpregnation gave the highest alkane conversions in the whole range of reaction temperatures studied. Factors such as Pt particle size or the oxidation state of platinum do not seem to be the responsible for the enhanced performance. Modification of the redox properties of the catalyst (i.e. high reducibility of vanadium species) likely provoked by the close contact between platinum particles and vanadium species and the partial introduction of vanadium in the platinum particles can be related to the improved reactivity of the PtV catalysts.

Kinetics of the propene oxidation over a Pt/alumina catalyst

Abstract This article reports the results obtained during the kinetic study of propene total oxidation on a platinum alumina catalyst in excess of oxygen. Reaction partial orders of propene and oxygen exhibited values of about − 0.5 and + 1, respectively. Propene presented a great inhibitory effect whereas an increase of oxygen concentration promoted the reaction. Based on TPD results, a Langmuir–Hinshelwood LH model considering propene to be adsorbed without dissociation was raised. A good agreement between experimental data and predicted results was observed. The value of the adsorption constants obtained confirmed that oxygen was more weakly adsorbed on the catalyst than propene.

Heterogeneous Enantioselective Hydrogenation in a Continuous-flow Fixed-bed Reactor System: Hydrogenation of Activated Ketones and Their Binary Mixtures on Pt–Alumina–Cinchona Alkaloid Catalysts

Under the experimental conditions of the Orito reaction the individual hydrogenation and the competitive hydrogenations of three binary mixtures of methyl benzoylformate (MBF), pyruvic aldehyde dimethyl acetal (PA) and 2,2-diethoxyacetophenone (DAP) on platinum–alumina catalysts modified by cinchonidine, cinchonine, quinine and quinidine (Pt–CD, Pt–CN, Pt–QN, Pt–QD) were studied for the first time using continuous-flow fixed-bed reactor system. Conversions of chiral (Cc) and racemic (Cr) hydrogenations of all three compounds and enantioselectivities (ee) were determined under the same experimental conditions (under 4 MPa H2 pressure, at room temperature using toluene/AcOH 9/1 as solvent).The order of the rates of the enantioselective hydrogenations of the three substrates studied is MBF > PA > DAP, and the order of their ee values is MBF ~ PA > DAP. The hydrogenation rate and the effect of rate on ee depend on the structure of the cinchona used: hydrogenation of MBF and PA may produce ee values over 90 %, however, the ee values were conspicuously low in the presence of Pt–QN and especially of Pt–QD catalysts. In the chiral hydrogenation of DAP considering racemic hydrogenation rate decrease (Cc/Cr < 1) takes place instead of rate enhancement over all four catalysts. The new experimental data supported the so far known fundamental rules of the Orito reaction based on batch studies.

Joint aromatization of butane and hexane on alumina-platinum catalysts

It has been found that the joint aromatization of C4 and C6 alkanes proceeds during the conversion of a butane and hexane mixture on alumina-platinum catalysts. It has been shown that a necessary condition for realization of the joint aromatization is the presence of highly dispersed platinum as ionic species (Ptσ) and “hard” Lewis acid sites (Lz) of a catalyst. It has been determined that an optimum Lz/Ptσ ratio for joint conversion reaction of light alkanes is from 1 to 2.

Evaluation of catalyst prepared in microchannel with in situ FT-IR microscopy

In situ characterization of silicon micro channel reactor with supported platinum alumina catalyst prepared on the channel wall was conducted with FT-IR microscope under propane flow, propene flow and cyclohexane flow. Surface π-allylic species along with surface OH group were observed at 373K under propane or propene flow. These species were rather stable under N2 flow and H2 flow. The reactor was active for dehydrogenation of cyclohexane to produce benzene and cyclohexene. In situ FT-IR observation under flow of cyclohexane at 473K, decrease of reactant, increase of products, a maximum of π-allylic and CC species were observed from inlet toward outlet. The maximum absorbance of the intermediate shifted with flow rate. These suggested consecutive reaction path and existence of film resistance.

Alumina-platinum catalyst in the reductive dehydration of ethanol and diethyl ether to alkanes

The reductive dehydration of ethanol and diethyl ether selectively occurs with the formation of alkanes to C10+ on an AP-64 alumina-platinum catalyst (0.6 wt % Pt/γ-Al2O3) after its reduction with hydrogen at 450°C for 12 h in Ar. It was found that one of the main reaction paths is the insertion of ethylene into substrate intermediates with the predominant formation of normal alkanes. It was found by XAFS spectroscopy that Pt2Al intermetallide particles were formed along with platinum metal clusters after long reduction. The ammonia TPD data indicated a change in the acid properties of the surface after the long reduction of the catalyst: the concentration of medium-strength surface aprotic acid sites increased by a factor of 2. It was found that the interaction of aprotic sites with water vapor resulted in the formation of strong proton acid sites. It is likely that these latter are responsible for the growth of a carbon skeleton in the course of alkane formation from ethanol.

Study of n-hexane isomerization on Pt/SO4/ZrO2/Al2O3 catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO4/ZrO2/Al2O3 catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al2O3 alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO4/ZrO2/Al2O3 superacid catalyst were used in this study. With the use of IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.

Effects of the modification of reforming alumina-platinum catalysts with zirconium

The effects of the modification of supported platinum as a constituent of reforming Pt/Al2O3 and Pt-Re/Al2O3 catalysts by introducing zirconium, which was obtained from various starting compounds, into the composition of the support were studied. These effects were most pronounced if difficult-to-hydrolyze compounds served as a source of zirconium. It was found that zirconium affected the metal-support interaction strength, which is responsible for the formation of the most strongly adsorbed hydrogen species (over the temperature range of 300–500°C). This suggests a change in the electronic state of platinum under the action of zirconium. Platinum sites became more regular; as a result of this, the reaction rate parameters of heptane conversion changed.

Joint conversion of butane and hexane in the presence of supported platinum catalysts

It has been found that the joint conversion of butane and hexane over alumina-platinum catalysts opens up a new route of butane conversion yielding C4+ hydrocarbons with an increased yield of the C6+ products on a converted hexane basis. It has been shown that a necessary condition for the occurrence of this reaction is the presence of finely divided platinum in the ionic form (Ptσ) in the catalysts. The results of catalytic testing of the samples modified with Cl−and F− anions allowed a possible mechanism and the nature of active sites of the reaction of the joint conversion of butane and hexane to be proposed.

Sorption-luminescence determination of gold, silver, and platinum with the use of silica gel chemically modified with N-(1,3,4-thiodiazole-2-thiol)-N′-propylurea groups

Silica gel chemically modified with N-(1,3,4-thiodiazole-2-thiol)-N′-propylurea extracted gold(III) from solutions in the range of 6 M HCl-pH 8 and silver(I) from nitric acid solutions in the range of 6 M HNO3-pH 8 and 1–2 M HCl at 20°C with 99.0–99.9% recovery and a sorption equilibration time of 5 min. Platinum(II) was quantitatively extracted at room temperature from solutions in the range of 4 M HCl-pH 8; the sorption equilibration time was 20 min. For the quantitative extraction of platinum(IV), it should be reduced to platinum(II). The intense yellowish orange luminescence (λmax (Au) = 575 nm, λmax (Ag) = 550 nm, and λmax(Pt) = 620 nm) of surface complexes at 77 K under UV irradiation was used in the development of procedures for the low-temperature sorption-luminescence determination of gold, silver, and platinum. The detection limits were 0.15 (Au), 0.1 (Ag), and 0.05 μg (Pt) per 0.1 g sorbent. The calibration function was linear to 50 (Au, Ag) or 80 μg (Pt) per 0.1 g sorbent. The relative standard deviation in the determination of more than 5 μg of a metal was no higher than 6%. The sorption-luminescence determination procedures were tested in the determination of gold in gold-containing concentrates and their processing products and platinum in alumina-platinum catalysts.

Kinetics of the low-temperature isomerization of n-hexane on the NIP-3A catalyst in an isothermal flow reactor

Low-temperature n-hexane isomerization kinetics was studied in an isothermal fixed-bed flow reactor on the chlorinated platinum-alumina catalyst NIP-3A under conditions of the coexistence of liquid and vapor phases. Optimum n-hexane isomerization conditions have been determined. Kinetic equations for the process are suggested.

Electronic effects in the coke deactivation of platinum-alumina catalysts

By means of XPS, ESR, DTA, and pyridine flash desorption techniques; micropulse reactor studies; and quantum-chemical calculations, it was shown that, during the coking of platinum-alumina catalysts in hydrocarbon media, the electron density of the platinum atom increases up to the formation of Pt0, which is a deactivating factor from the viewpoint of the electronic effects. The stabilization of the activity of platinum-alumina catalysts consists in an increase in the effective positive charge on the platinum atom; this function is fulfilled by modifier elements. It was found that the platinum protection mechanism differs, depending on the nature of the modifying additive: certain elements function via another, additional mechanism of catalyst stabilization, the blocking action. The theoretical conclusions made in this study are corroborated by the results of testing a new, Pt-Sb-Re catalyst supported on Al2O3-Cl with predicted properties.