Alumina-supported Platinum Catalysts Research Articles

Kinetics Study of Hydrogen Combustion over Pt/Alumina Catalyst

Combustion of hydrogen releases energy but in many applications, catalytic combustion of hydrogen may prove advantageous over direct combustion. The main advantage of catalytic combustion of hydrogen is that heat can be obtained at lower temperatures as well. The activity of catalyst for combustion of lean mixtures (< 2%) of hydrogen was studied in the present work and the kinetics of catalytic combustion of hydrogen has been established. The combustion of hydrogen on alumina supported platinum catalyst starts at above 323 K. Two reaction models have been investigated for possible mechanism of the reaction. The kinetics follows Hougan-Watson model where both hydrogen and oxygen adsorb on same site; hydrogen undergoes dissociative chemisorption and surface reaction being the slowest step. However, a simplified power law type rate equation was also established which adequately fits the experimental data for temperature between 373 and 673 K.

Insights into Pt–CN species on an alumina-supported platinum catalyst as active intermediates or inhibitors for low-temperature hydrogen cyanide synthesis from methane and nitric oxide

In situ measurements revealed that the Pt–CN species function not only as intermediates but also as inhibitors for low-temperature HCN synthesis.

Particle Size Effect on Hydrogen Cyanide Synthesis with CH<sub>4</sub> and NO over an Alumina-supported Platinum Catalyst

白金担持アルミナ上で，一酸化窒素（NO）を酸化剤としてメタンをシアン化水素（HCN）に変換する際の白金ナノ粒子の粒径効果について検討した。担持量と焼成温度を制御することにより，1.6〜4.1 nmの範囲で様々な平均粒子径のPt触媒を得ることができた。Pt表面サイト量はパルス法によるCO滴定で決定し，触媒活性は同一接触時間下で評価した。Pt の粒子が小さい触媒（1.6〜3.2 nm）では，NO 転化率が粒子径の大きい触媒よりも低いことが分かった。粒子径の大きな触媒（4.1〜4.2 nm）は，10 wt% Pt/Al2O3 において 400 ℃で 収率1.3 %（炭素ベース）で高い HCN 選択率（53.5 %）を示した。大きなPt粒子が高い活性を示す理由の一つは，金属と担体の界面で進行するHCNから二酸化炭素とアンモニアへの逐次反応を抑制したためと思われる。Pt L3端X線吸収微細構造（XAFS）スペクトルから，反応試験後の小粒子触媒はPt–CN種で覆われていることが分かった。一方，大粒子触媒ではPt–COが主な吸着種として観測され，大粒子触媒の方がHCN脱離が容易であることが示唆された。

Promotion effect of sulfur impurity in alumina support on propane dehydrogenation

Alumina materials are widely applied either as a catalyst or support in various industrial catalytic processes. Impurities in alumina that are unfriendly to catalytic performance are inevitably present during the production processes. Facing this problem, we here report that the use of sulfur-containing alumina as the support can generate active alumina-supported platinum catalyst, which exhibits superior propylene selectivity and anti-coking ability during propane dehydrogenation. It demonstrated that the sulfur impurity in alumina is not entirely detrimental. During the reduction process, the formation of gas-phase sulfur species increased the electrons and poisoned unsaturated sites of platinum particles. The sulfur impurity in alumina can be removed through a hydrogen reduction process, and the degree of desulfurization is correlated with the operating temperature. This study demonstrated that the rational use of impurity will contribute to the design of a catalyst with high reactivity for potential applications.

Low-Temperature Activation of Methane with Nitric Oxide and Formation of Hydrogen Cyanide over an Alumina-Supported Platinum Catalyst

This study demonstrated methane activation with subsequent conversion to hydrogen cyanide (HCN) at low temperatures using nitric oxide (NO) as the sole oxidant together with an alumina-supported platinum catalyst (Pt/Al2O3). This process afforded HCN even at 300 °C, indicating that C–H bond cleavage, NO dissociation, and simultaneous C–N coupling all occurred at this reduced reaction temperature. The HCN yield increased with increasing temperature, resulting in a 3.2% yield with a selectivity of 49% at 425 °C. This yield was much greater than that obtained from the reaction of CH4 with NH3 and O2, which suggests a reaction mechanism different from the Andrussow process. The HCN production rate was 11.4 mmol g–1 h–1 and the corresponding turnover frequency was 253 h–1, both of which were far superior to those obtained in previous studies at similar reaction temperatures. The Pt catalyst was found to be stable and could continuously produce HCN for at least 100 h. In situ X-ray absorption fine structure analyses suggested that the high resistance of this material to deep oxidation facilitated HCN formation. The difference between X-ray absorption near-edge structure spectra before and during the reaction indicated that the specific adsorbates on the catalyst were dependent on the reaction temperature and that the extent of adsorbed Pt-CN species was correlated with the reactivity of the material.

Synergistic effects of Pt-embedded, MIL-53-derived catalysts (Pt@Al2O3) and NaBH4 for water-mediated hydrogenolysis of biomass-derived furfural to 1,5-pentanediol at near-ambient temperature

We demonstrate an effective and selective conversion of biomass-derived furfural (FAL) to 1,5-pentanediol (1,5-PD) with high yields through a water-mediated hydrogenolysis process under mild reaction conditions (45 °C, aqueous media). A novel alumina-supported platinum catalyst (Pt@Al2O3) with high-loading and uniform distribution of Pt nanoparticles is prepared through in situ synthesis of Pt-embedded metal–organic frameworks (i.e., MIL-53(Al)-NH2). As a typical example, a high yield of 75.2% 1,5-PD can be achieved from FAL conversion. A possible reaction mechanism is proposed based on the experimental and computational findings, including XPS analysis, kinetic studies, acidity measurements, and density functional theory (DFT) calculations. The high effectiveness of the proposed system is attributed to (1) the strong metal support interaction (SMSI) between Pt and penta-coordination aluminum, and (2)the synergistic effects of Brønsted acidic alumina support and the presence of sodium metaborate (NaBO2). Sodium borohydride (NaBH4) acts as both a hydrogen donor and a precursor for NaBO2, which results in an exclusive FAL to 1,5-PD (i.e., no 1,2-pentanediol) by regulating the water-mediated hydrogenolysis pathway as revealed by experiments and DFT calculations. The reaction strategy proposed in this study has also manifested remarkable versatility for a wide range of furan derivatives.

Carbon Formation and Active Site of Alumina Supported Platinum Catalyst in Steam Methane Reforming Containing Sulfur

Effect of sulfur poisoning on Pt/α-Al2O3 catalysts in steam methane reforming (SMR) was investigated using dimethyl sulfide (DMS). SMR with and without 10 ppm DMS addition was performed over 0.1-2.0 wt% Pt/α-Al2O3 catalysts. Catalyst deterioration occurred at an early stage, but not inactivation in the presence of DMS. Moreover, after the supply of DMS was stopped, the activity was completely restored. DMS in the reaction gas also caused severe sintering of the Pt particles and promoted carbon formation on the 1.0-2.0 wt% Pt catalysts. On the other hand, carbon formation did not occur on the 0.1 wt% Pt catalysts. The Pt sintering and carbon formation behaviors were independent of the SMR activity. These results suggest that three different active sites are formed on the Pt/α-Al2O3. The first is a SMR active site not affected by DMS. The second is an active site that loses activity due to DMS, but completely regenerates after the supply of DMS is stopped. The third is not an active site of SMR but where sintered Pt accelerates methane decomposition to produce carbon.

Hydrolysis of carbonyl sulfide over modified Al2O3 by platinum and barium in a packed-bed reactor

The integrated gasification combined cycle (IGCC) has been applied as an alternative technology for power plant due to the higher thermal efficiency than that of conventional pulverized coal-fired technology. However, syngas produced from coal gasification in IGCC is usually contaminated with carbonyl sulfide (COS). Therefore, it is necessary to be treated before being utilized in gas turbine or chemicals production. In this paper, catalytic treatment of COS by hydrolysis over alumina-supported platinum (Pt/Al2O3) catalysts was investigated. COS was hydrolyzed and converted to hydrogen sulfide (H2S) in a packed-bed reactor under flue-gas in a temperature range of 150–250 °C, and Weight Hourly Space Velocity (WHSV) of 7,000 hr−1. The optimal Pt/Al2O3 catalysts were determined by varying active Pt metal (0.1–1.0 wt%) loadings and barium promoter (1–5 wt%) loadings. The prepared catalysts were characterized by X-ray diffraction (XRD), N2 adsorption and desorption, and Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM/EDX). It was found that the activity of Al2O3 drastically dropped from 90 to 10% after 510 min time on stream. The addition of Pt and Ba onto Al2O3 could stabilize the catalytic activity. The 0.5%Pt/5.0%Ba/Al2O3 catalyst provided the best performance in COS hydrolysis. The complete COS conversion was achieved with 0.5%Pt/5.0%Ba/Al2O3 in all initial concentrations, and the lifespan of the catalyst was prolonged. A kinetic model of this reaction was also purposed. Sulfur poisoning and carbon deposition on the catalyst surface caused the catalyst deactivation.

Aluminum Oxide–Supported Manganese Oxide Catalyst for a 98% Hydrogen Peroxide Thruster

Silica-doped alumina–supported catalyst, containing manganese oxides, doped with cobalt oxide, was prepared in situ by wet impregnation, vacuum drying, and calcination at 700°C. Potassium permanganate and cobalt nitrate were used as precursors and thermally decomposed. The active phase content was determined by simple mass measurement. Subsequently, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and physical adsorption by Brunauer-Emmet-Teller tests have been carried out to determine the morphology, chemical and phase composition, and specific surface area. The catalyst was subjected to the real-environment testing in a packed catalyst bed of a small rocket engine; 98% hydrogen peroxide was applied as propellant. At the design stage of a packed catalyst, it was assumed that a bed loading varied from 24.5 to . The total propellant throughput was 5.43 kg. After the test campaign, the microscopic observation of the structure and physisorption were repeated to describe changes in the structure of the active phase. Test parameters and their change in time were analyzed. The influence of structural and chemical changes between fresh and tested catalysts was taken into consideration. The quality of pure carrier and manganese oxides catalyst, for decomposition of 98% hydrogen peroxide, was investigated. A comparison of performance with alumina-supported platinum catalyst was presented and discussed.

Facile Route for Bio-Phenol Siloxane Synthesis via Heterogeneous Catalytic Method and its Autonomic Antibacterial Property.

Eugenol, used as bio-phenol, was designed to replace the hydrogen atom of hydrogenterminated siloxane by hydrosilylation reaction under the presence of alumina-supported platinum catalyst (Pt-Al2O3), silica-supported platinum catalyst (Pt-SiO2) and carbon nanotube-supported platinum catalyst (Pt-CNT), respectively. The catalytic activities of these three platinum catalysts were measured by nuclear magnetic resonance hydrogen spectrometer (1H NMR). The properties of bio-phenol siloxane were characterized by Fourier transform infrared spectrometer (FT–IR), UV-visible spectrophotometer (UV) and thermogravimeter (TGA), and its antibacterial property against Escherichia coli was also studied. The results showed that the catalytic activity of the catalyst Pt-CNT was preferable. When the catalyst concentration was 100 ppm, the reaction temperature was 80 °C and reaction time was 6 h, the reactant conversion rate reached 97%. After modification with bio-phenol, the thermal stability of the obtained bio-phenol siloxane was improved. For bio-phenol siloxane, when the ratio of weight loss reached 98%, the pyrolysis temperature was raised to 663 °C which was 60 °C higher than hydrogenterminated siloxane. Meanwhile, its autonomic antibacterial property against Escherichia coli was improved significantly.

Sub-Monolayer Control of Mixed-Oxide Support Composition in Catalysts via Atomic Layer Deposition: Selective Hydrogenation of Cinnamaldehyde Promoted by (SiO2-ALD)-Pt/Al2O3

Alumina-supported platinum catalysts have been modified with silicon oxide thin films grown using atomic layer deposition (ALD) in order to tune the acid–base and electronic properties of the oxide, and their performance has been tested for the hydrogenation of cinnamaldehyde. It was found that the silica layers greatly increase the stability of the platinum nanoparticles, preventing their sintering during high-temperature calcinations without affecting access to the metal surface in any significant way; the extent of CO adsorption, measured by infrared absorption spectroscopy was found to decrease by only one-third after 6 SiO2 ALD cycles. Additional Bronsted and Lewis acid sites were created upon the deposition of submonolayer coverages of silicon oxide, as probed via pyridine adsorption. The addition of the silicon oxide thin films reduced the overall activity of these catalysts but also increased their selectivity toward the production of the unsaturated alcohol. In addition, both turnover frequencies...

Catalytic Wet Air Oxidation and Neural Network Modeling of High Concentration of Phenol Compounds in Wastewater

Wastewater and other harmful compounds can be produced from different industrial activities and may contains toxic compounds like phenols. At high phenol concentrations, the carcinogenic effects are more likely and the environmental problems are of high concerns. In this study, the removal of a very high phenol concentration from refinery wastewaters by Catalytic Wet Air Oxidation was investigated and compared with the predicted results by neural network model. Alumina-supported platinum catalyst was prepared, characterized, and examined in a trickle bed reactor. A back propagation neural network model constructed in three layers was used to validate the experimental results. The first layer had five inputs that represent different operating conditions of feed acidity, weight hourly space velocity, pressure, time, and temperature; the second hidden layer had 18 neurons; and the third one was represented by one output, namely, phenol conversion percentage. The experimental results showed that the very high phenol concentration was successfully converted to a safe concentration and to acceptable concentrations of intermediates. The predicted phenol conversion of the neural network model shows the least error compared with the experimental test.

Hydrogen production on alumina-supported platinum catalysts

Hydrogen production is commercially performed by methane steam reforming over alumina-supported nickel catalysts, which deactivate by coke requiring improved catalysts. Aiming to find alternative catalysts for the reaction, the properties of Pt/Al2O3-MgO catalysts were studied in this work. It was found that small amounts of magnesium (Al/Mg (molar)=5) enter into alumina lattice and produce magnesium aluminate on the surface. For higher amounts (Al/Mg=2) only magnesium aluminate is produced. For even higher contents (Al/Mg=0.2) aluminum enters into magnesia lattice, producing magnesia and magnesium aluminate on the surface. The specific surface area, acidity and platinum dispersion changed with magnesium amount, the aluminum-richest catalyst (Al/Mg=5) showing the highest values. Consequently, the activity and selectivity of the catalysts change in methane steam reforming and in water gas shift reaction, different values of products yield and H2/CO being obtained. The sample with Al/Mg=5 is the most promising catalyst to produce hydrogen.

CO selective oxidation using Co-promoted Pt/γ-Al2O3 catalysts

In this work, alumina-supported platinum catalysts promoted with cobalt were analyzed in the preferential CO oxidation (PROX) reaction. The addition of Co represents a significant catalytic improvement with regard to the monometallic Pt catalyst. This improvement reaches its maximum with a Co/Pt atomic ratio of 1.5. The addition of a higher level of cobalt decreases the activity probably because it would produce the coverage of the Pt active sites, thus inhibiting the adsorption of CO. For all the bimetallic catalysts, the maximum conversion occurs at ca. 130 °C, a value which is within the acceptable working range for this process. A further temperature increase generates a decrease in the CO conversion. The studied catalysts presented a slight deactivation after several hours on stream. The original activity is recovered by submitting the catalysts to a reduction process at 500 °C. Results are explained in terms of TPR, DRS, EXAFS and XANES characterization of the catalysts.

Water-gas shift reaction on alumina-supported Pt-CeOx catalysts prepared by supercritical fluid deposition

Alumina-supported platinum catalysts, both with and without ceria, were prepared by supercritical fluid deposition and evaluated for activity for water-gas shift reaction. The organometallic precursor, platinum(II) acetylacetonate, was deposited from solution in supercritical carbon dioxide. Analysis of the catalysts by high resolution scanning transmission electron microscopy indicated that platinum was present in the form of highly dispersed metal nanoparticles. Pretreatment of the alumina-supported ceria in hydrogen prior to the deposition of the platinum precursor resulted in more platinum nucleated on ceria than non-pretreated alumina-supported ceria but varied in both particle size and structure. The ceria-containing catalyst that was not pretreated exhibited a more uniform particle size, and the Pt particles were encapsulated in crystalline ceria. Reaction rate measurements showed that the catalyst was more active for water-gas shift, with reaction rates per mass of platinum that exceeded most literature values for water-gas shift reaction on Pt-CeOx catalysts. The high activity was attributed to the significant fraction of platinum/ceria interfacial contact. These results show the promise of supercritical fluid deposition as a scalable means of synthesizing highly active supported metal catalysts that offer efficient utilization of precious metals.

Experimental and numerical investigation of hetero-/homogeneous combustion-based HCCI of methane–air mixtures in free-piston micro-engines

The hetero-/homogenous combustion-based HCCI (homogeneous charge compression ignition) of fuel–lean methane–air mixtures over alumina-supported platinum catalysts was investigated experimentally and numerically in free-piston micro-engines without ignition sources. Single-shot experiments were carried out in the purely homogeneous and coupled hetero-/homogeneous combustion modes, involved temperature measurements, capturing the visible combustion image sequences, exhaust gas analysis, and the physicochemical characterization of catalysts. Simulations were performed with a two-dimensional transient model that includes detailed hetero-/homogeneous chemistry and transport, leakage, and free-piston motion to gain physical insight and to explore the hetero-/homogeneous combustion characteristics. The micro-engine performance concerning combustion efficiency, mass loss, energy density, and free-piston dynamics was investigated. The results reveal that both purely homogeneous and coupled hetero-/homogeneous combustion of methane–air mixtures in a narrow cylinder with a diameter of 3mm and a height of approximately 0.3mm are possible. The coupled hetero-/homogeneous mode can not only significantly improve the combustion efficiency, in-cylinder temperature and pressure, output power and energy density, but also reduce the mass loss because of its lower compression ratio and less time spent around TDC (top dead center) and during the expansion stroke, indicating that this coupled mode is a promising combustion scheme for micro-engine. Heat losses result in higher mass losses. Heterogeneous reactions cause earlier ignition, which is very favorable for the micro-device.

Selective Ring-Shift Isomerization in Hydroconversion of Fluorene over Supported Platinum Catalysts

Hydroconversion of fluorene has been conducted over the zeolites and silica–alumina-supported platinum catalysts. The hydrogenation of aromatic rings, the hydroisomerization of the cycloalkanes, and the cracking reaction over the Pt/Y zeolite catalysts are studied to give a detailed hydroconversion reaction network of fluorene through conversion of the synthesized intermediates. Compared to the β-zeolites and silica–alumina supports used, the dispersed platinum catalysts on the Y-zeolites with unique cage structure and acidic properties selectively catalyze the ring-shift isomerization of perhydrofluorene with high yields of the dodecahydrocyclopenta[a]naphthalene and dodecahydrophenalene. Such hydroisomerization reaction is enhanced above 250 °C, while more cleavage of carbon–carbon bond occurs at higher temperatures (280–290 °C) which lead to the great production of single-ring cycloalkanes and more loss in carbons. In the comparative study of the support effect, an examination of the product yields ind...

Catalytic destruction of vinyl chloride over an alumina–supported platinum catalyst

In this study, vinyl chloride (VC), the primary material for manufacturing polyvinyl chloride (PVC), is decomposed via catalytic oxidation (C-OX) using Pt/γ-Al2O3 catalyst. The effects of related major factors such as reaction temperature (T) and gas hourly space velocity on the conversion of VC (X) were examined. The values of T for achieving conversions of 50% and 90% are 504 and 580 K with C-OX, respectively, whereas those without Pt/γ-Al2O3 (i.e., thermal oxidation, T-OX) are 900 and 983 K, respectively, thus indicating that C-OX significantly reduces T for effective oxidation of VC to form CO2, HCl, and Cl2 when compared with T-OX. The mineralizations of carbon in VC to form CO2 are 75.5% and 38% for C-OX and T-OX, respectively, at 90% X. The conversions of chlorine atom in 1,2-dichloroenane (DCEA) to Cl in HCl and Cl2 are approximately 42% and 50.8% for C-OX and T-OX, respectively, at 90% X. These results indicate that the Pt/γ-Al2O3 catalyst exhibits remarkable performance for the mineralizations to form CO2 even though a proportion of chlorine atoms are adsorbed on the Pt surface. The Eley–Rideal model can be used to describe the experimental results, thus yielding activation energy and frequency factor values of 49.0 kJ mol−1 and 1.77 × 106 s−1, respectively. The obtained information and kinetic parameters are useful for the rational design and operation of C-OX process for the abatement of VC.

Pt Catalyst over SiO2 and Al2O3 Supports Synthesized by Aerosol Method for HC-SCR DeNOx Application

ABSTRACTSilica-supported platinum (Pt/SiO2) and alumina-supported platinum (Pt/Al2O3) catalysts have been prepared by an aerosol spray pyrolysis method. Systematic characterization of each catalyst using TEM, XRD, and XPS revealed that crystalline and metallic Pt nanoparticles were well dispersed on the surface of silica and alumina supports. The sintering effect on Pt particles over Al2O3 at high temperature (~250°C) is more prominent than those over SiO2; this suggests that there is stronger interaction between Pt particles and SiO2 support, when compared to Pt over Al2O3 support, resulting in Pt particles size below 3 nm. Moreover, steady-state catalytic experiments for selective reduction of nitrogen monoxide by propene have demonstrated that NOx conversions to N2O and N2 in Pt/SiO2 and Pt/Al2O3 catalysts are 29.8% and 55.8% at 250°C, respectively.

Alumina-supported platinum catalysts: Local atomic structure and catalytic activity for complete methane oxidation

The structure of platinum species in a model set of monodisperse Pt/γ-Al2O3 catalysts was studied using radial distribution function (RDF) of electron density. Catalyst preparation conditions were revealed to considerably affect the dispersion and structure of supported platinum. Cation vacancies on the γ-Al2O3 surface were essential to anchor electron deficient platinum atoms and clusters. Platinum segregation with forming finely dispersed metal particles was evident in some catalysts. The methane total oxidation over the Pt/γ-Al2O3 catalysts was established to depend strongly on the platinum oxidation state. The catalysts containing oxidized platinum species and highly dispersed oxidizable Pt0 particles were more active. The metal–support interaction improved the performance of the catalysts indirectly, by stabilizing the platinum dispersion.