Palladium-alumina Catalyst Research Articles

Performance of the ρ- Al2O3 based Ag promoted Pd/ Al2O3 catalyst during Acetylene hydrogenation with an ideal feed

Catalytic hydrogenation of acetylene was studied with an ideal feed with a catalyst prepared from different alumina support and with varying quantities of promoter addition. Silver promoted palladium alumina catalysts were prepared on the transition alumina, ρ-alumina and the catalyst performance was compared with the traditional palladium alumina catalyst based on α-alumina. The catalyst supports were prepared using the granulation technique and sequential impregnation method was used for the catalyst preparation. The silver metal loading was varied in the catalysts and the impact of varied promoter quantity was also studied. The supports were characterized for the acidity, alumina phase, and catalyst characterization was done using TEM, TPR, and BET method to understand the difference between catalysts prepared on different types of alumina support. A fixed bed catalyst reaction was used for the performance evaluation and an ideal gas with acetylene and nitrogen was used as the feed. The catalyst evaluation gives the comparative performance of the catalysts at different temperature conditions. Acetylene conversion and ethylene selectivity in the product were evaluated. The spent catalyst analysis was done using TGA and CHN analysis was performed to understand the carbon deposition and by-product formation during the reaction with different types of catalysts.

Influence of different alumina phases on the catalytic properties of palladium-alumina catalysts for selective hydrogenation of acetylene to ethylene

Influence of different alumina phases on the catalytic properties of palladium-alumina catalysts for selective hydrogenation of acetylene to ethylene

Palladium dispersion effects on wet methane oxidation kinetics

The catalytic activity for dry and wet methane oxidation over a series of palladium–alumina catalysts with systematically varied palladium loadings and PdO dispersions was measured and compared with conceptual multiscale simulations.

Pinning down the water-gas shift mechanism

Industry has depended on the water-gas shift (WGS) reaction for more than a century. The WGS process, which combines carbon monoxide and water to form carbon dioxide and hydrogen, is a key component of industrial plants that use hydrogen to process hydrocarbons or to synthesize ammonia or methanol. The intimately related reverse process, RWGS, consumes CO2, a greenhouse gas, and generates CO, a valuable reagent. This chemistry has a long history, yet scientists continue to debate the nature of the catalytically active site and reaction pathway, key pieces of information needed for improving catalyst performance. Vassiliki-Alexandra “Vanda” Glezakou, Janos Szanyi, and coworkers at Pacific Northwest National Laboratory hope to end the debate. In a study combining spectroscopy, kinetics, and computations, the team analyzed the RWGS reaction driven by a palladium-alumina catalyst. They found that the key intermediate is a carboxylate species that bridges palladium and aluminum atoms (shown) and that

A sustainable mesoporous palladium-alumina catalyst for efficient hydrogen release from N-heterocyclic liquid organic hydrogen carriers

Liquid organic hydrogen carriers (LOHC) are interesting hydrogen vectors which can exploit existing infrastructure. Specifically, N-heterocyclic compounds are attractive due to lower dehydrogenation enthalpy than homocyclic ones and demand a viable palladium catalyst to guarantee high dehydrogenation activity at low temperatures and stability in recycle runs. Here, we employ one-pot solvent deficient precipitation yielding a mesoporous palladium-alumina. The prepared catalyst system offers higher hydrogen release capability by 20% than conventional palladium/γ-Al2O3 in the dehydrogenation of four different N-heterocyclic compounds at or below 250 °C. Futhermore, it shows negligible activity loss up to five consecutive runs for perhydro 2-(n-methylbenzyl)pyridine and perhydro 2-methylindole. Such dehydrogenation performance is caused by the solvent deficient environment that restricts palladium mobility by contiguous alumina particles and produces well-dispersed palladium phase with a higher density of (111) plane. Therefore, the reported synthesis method may contribute to the production of innovative dehydrogenation catalysts for LOHC compounds.

Characterization and study on the thermal aging behavior of palladium–alumina catalysts

A series of Pd/Al2O3 catalysts were prepared by incipient wetness impregnation method. Palladium loading was varied in a range of 0.125–4.0 mass%. The catalytic performance of the samples was tested in model reaction of CO oxidation at oxygen excess. Catalysts were characterized by temperature-programmed reduction (TPR), electron paramagnetic resonance, and UV–visible spectroscopy. Thermal aging of chosen samples was performed at 1000 °C. The thermal aging behavior was studied using TPR, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). It was shown that palladium stabilized in the form of dispersed surface Pd2+ species when Pd loading is 0.5 mass% and below. Samples with higher loading preferentially contain nanosized Pd particles. Agglomeration of Pd species during thermal aging was found to take place starting from Pd concentration of 1.0 mass%. In some cases, size of Pd particles exceeds 150 nm, which is in about 40 times higher comparing with the initial samples. According to XPS data, degree of Pd2+-alumina interaction in the aged samples is also increased.

Aluminium doped ceria–zirconia supported palladium-alumina catalyst with high oxygen storage capacity and CO oxidation activity

The Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst prepared by a mechanochemical route and calcined at 1000°C for 20h in air atmosphere to evaluate the thermal stability. The prepared Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst was characterized for the oxygen storage capacity (OSC) and CO oxidation activity in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy and the Brunauer–Emmet–Teller (BET) technique were employed. The OSC values of all samples were measured at 600°C using thermogravimetric-differential thermal analysis. Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst calcined at 1000°C for 20h with a BET surface area of 41m2g−1 exhibited the considerably high OSC of 583μmol-Og−1 and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO2/Pd-γ-Al2O3 and Ce0.5Zr0.5O2/Pd-γ-Al2O3 for comparison.

A New Oxygen Storage Capacity Material of a Tin-doped Ceria–Zirconia-supported Palladium–Alumina Catalyst with High CO Oxidation Activity

Abstract The Ce0.5Zr0.4Sn0.1O2/Pd–Al2O3 composite prepared by a mechanochemical route, with a high BET surface area of 38 m2 g−1, exhibited a high oxygen storage capacity (OSC) and high CO oxidation activity at low temperatures, even after calcination at 1000 °C for 20 h.

The significance of the order of impregnation on the activity of vanadia promoted palladium-alumina catalysts for propane total oxidation

The increased activity of alumina-supported palladium catalysts promoted with vanadium oxide has been investigated. Three different vanadium promoted Pd/Al2O3 catalysts with the same composition but synthesized employing sequential and co-impregnation were tested for the total oxidation of propane. The order of impregnation was critical to produce high activity catalysts. Vanadium and palladium co-impregnation on the Al2O3 support led to the most active catalyst, whereas the step-wise impregnated catalysts show a catalytic performance similar to or slightly better than unpromoted palladium catalysts. The high activity of the co-impregnated catalysts is related to the particle size and oxidation state of the palladium particles; and to the redox properties of vanadium species. The most active catalyst presents relatively large palladium particles in combination with increased reducibility of vanadium species and a relatively high amount of V4+ within the bulk of the catalyst and on the surface. STEM shows that, compared to catalysts containing only Pd or V, co-addition of the Pd and V species drastically altered the particle size distribution and morphology of the PdOx particles, and simultaneously caused the monolayer dispersion of the VOx species to become much patchier in nature. It also showed that the microstructure of the catalysts was similar for the different orders of impregnation, but some differences between the morphology of PdOx particles were observed.

Hydrogenation of Succinic Acid to γ-Butyrolactone (GBL) Over Palladium-Alumina Composite Catalyst Prepared by a Single-Step Sol–Gel Method

Mesoporous palladium-alumina (Pd-A) composite catalysts prepared by a single-step sol–gel method were calcined at various temperatures to control palladium surface area and acidity. The Pd-A catalysts were characterized by XRD, BET, N2 adsorption–desorption isotherm, H2 chemisorption, 27Al MAS NMR, NH3-TPD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to γ-butyrolactone (GBL) was carried out over Pd-A catalyst in a batch reactor. The effect of calcination temperature of Pd-A catalyst on the palladium surface area and catalytic performance was investigated. In the hydrogenation of succinic acid, conversion of succinic acid increased with increasing palladium surface area of Pd-A catalyst. Selectivity for GBL depended on the formation of succinic anhydride (an intermediate product formed by acid catalysis) and by-products (formed by hydrogenolysis). Nevertheless, yield for GBL also increased with increasing palladium surface area of Pd-A catalyst. Thus, palladium surface area played an important role in enhancing the catalytic performance of Pd-A catalyst in the hydrogenation of succinic acid to GBL. In the hydrogenation of succinic acid to γ-butyrolactone (GBL) over Pd-A catalyst (mesoporous palladium-alumina composite catalyst prepared by a single-step sol–gel method), conversion of succinic acid and yield for GBL increased with increasing palladium surface area of the catalyst. .

The Effect of Support Nature and the Temperature of Preliminary Calcination on the Atomic Catalytic Activity of Supported Palladium Catalysts for the Complete Oxidation of Hydrocarbons

It is shown that for palladium catalysts supported on various supports, there is no effect of thermal activation consisting of an increase in the turnover number (TON) of palladium with an increase in the temperature of sample calcination from 500 to 700°C, as was observed in the case of similar supported platinum catalysts; for two palladium–alumina catalysts calcined at 500°C and differing in the concentration of palladium and dispersity, the TON of low-dispersity palladium is substantially higher than the TON of high-dispersity palladium; all other conditions being the same, the TON of supported palladium is determined by the support nature.

MOSSBAUER STUDY OF 119SN-PD CATALYSTS FOR SELECTIVE HYDROGENATION OF HEXA-1,5-DIENE

The addition of tin to palladium-alumina catalysts induces significant modifications of the catalytic properties of palladium in the hydrogenation of hexa-1,5-diene. The influence of the support, of the metal loading and of the preparation method on the chemical state of tin in Pd-Sn/Al2O3 catalysts are studied by Mossbauer spectroscopy. In reduced catalysts, about 60% of tin is present as Sn(0), which forms different Pd-Sn compounds, that are responsible for the changes in the catalytic performances.

Palladium catalyzed synthesis of methylamines from carbon dioxide, hydrogen and ammonia

The synthesis of methylamines from carbon dioxide, hydrogen, and ammonia has been studied over two palladium-alumina catalysts with palladium loadings of 2.8 and 7.6 wt%, respectively. Catalytic tests were performed in a fixed-bed microreactor at 0.6 MPa total pressure in the temperature range 473--573 K. The catalysts showed high activity for methylamine formation at low temperatures and produced monomethylamine with selectivities higher than 80%, besides of smaller amounts of di- and trimethylamine. Other carbon containing products observed were carbon monoxide, formed by the reverse water-gas shift reaction, and methane, which was the prevailing product above 573 K. In situ diffuse reflectance FTIR studies were performed to identify the species present on the catalyst surface under reaction conditions. Ammonia and methylamines are adsorbed on Bronsted and Lewis acid sites on the catalyst. Evidence is given that surface formate and isocyanate species are present on palladium-alumina under reaction conditions.

Gas Chromatographic Analysis of Oxygen and Argon at Room Temperature

A simple and accurate method for the analysis of oxygen and argon at room temperature with a dual-column gas chromatographic system is described. The system consists of a 5A molecular sieve (MS 5A) column and a combination column (MS 5A and palladium alumina catalyst). The MS 5A column is used to separate the air sample into two main peaks at room temperature: an argon and oxygen combined peak and a nitrogen peak. The combination column is used to separate the argon and oxygen peaks; the oxygen is eliminated due to the catalytic reaction with hydrogen (hydrogen is used as the carrier gas), so only the argon peak is eluted. The concentrations of oxygen and argon can be calculated by comparing the output of both columns.

Spectroscopic study of the interaction of carbon monoxide with cationic and metallic palladium in palladium–alumina catalysts

Palladium–alumina catalysts prepared from various precursors and by different preparation methods have been studied after calcination by O2 and reduction by H2, using IR spectroscopy of adsorbed CO, EPR and diffuse reflectance measurements. In addition to Pd2+ ions, the unreduced samples contain Pd3+ and Pd+ species. Pd2+ and Pd– entities are still present on catalysts reduced at 573 K. The influence of the precursor on the metal fraction exposed (MFE) and on the nature of adsorbed CO species is clearly shown. Bridged entities are more sensitive to the MFE value than the linear ones. At 100 Torr [1 Torr ≈(101 325/760) Pa], the bridged entities are compressed, which leads to a CO-(surface Pd) ratio of near unity. The MFE increases when the precursors are taken in the following order nitrate < chloride (impregnated)≈ acetylacetonate < chloride (exchanged). The sintering brought about by increasing the reduction temperature seems to affect the largest metal particles rather than the small ones which strongly interact with the carrier.

Adsorption of Benzene during Benzene Hydrogenation over Palladium-Alumina Catalyst

Adsorption of Benzene during Benzene Hydrogenation over Palladium-Alumina Catalyst

Kinetics of the Liquid-Phase Oxidation of Ethanol by Oxygen over a Palladium-Alumina Catalyst

The oxidation of ethanol to acetate ion by gaseous oxygen in an aqueous sodium carbonate solution with 0.5Vertical Bar3< palladium-on-alumina as catalyst was carried out in a jacketed, 1 gal stirred autoclave at 33-37 mm Hg above atmospheric and at 25/sup 0/, 35/sup 0/, and 45/sup 0/C to determine reaction kinetics. The rate was essentially first order in oxygen, increased with ethanol concentration in the range 0.45-1.80 g-mole/l., and exhibited a maximum with respect to sodium carbonate concentration at 0.1 g-mole/l. The tortuosity factor for the alumina catalyst support was 2.9. The reaction will serve as a model for studying fast gas-liquid-solid reactions.

Auger spectroscopic study of the poisoning of a commercial palladium-alumina hydrogenation catalyst

A commercial palladium-alumina catalyst used for the selective hydrogenation of diolefins in an olefin-aromatic-paraffin stream had lost most of its hydrogenation activity. It was examined by Auger electron spectroscopy after other typical physical measurements on the spent catalyst had failed to clearly establish the cause or causes of catalyst deactivation. Surface areas and levels of S and Cl in the fresh and the spent catalysts were not significantly different. However, iron to the extent of 1.7% by weight was found on the spent catalyst. This level of iron on a ~200 m 2/g surface area support is not necessarily a poison. However, Auger surface analysis has now revealed that iron was coating a majority of the palladium catalyst surface thereby masking (and poisoning) the active Pd surface atoms as well as the atoms of the promoters like Cr and Mo. The iron deposited on the catalyst came from a bad batch of feedstock. The surface analysis by Auger electron spectroscopy also revealed substantial amounts of surface Ca and large gradients of Pd, Cr, and Mo, from the outside to the inside of the pellets. The spent catalyst also had much higher amounts of iron on the outside than the interior surface of the catalyst pellets.

Study on the Selective Hydrogenation of Butadiene in C&lt;sub&gt;4&lt;/sub&gt;-Hydrocarbon Fraction (Part 1)

Selective hydrogenation of butadiene to remove the butadiene from C4 hydrocarbon fraction has been studied over palladium-alumina catalyst at elevated pressure. The following results were obtained.(1) Presulfiding of the catalyst and presence of sulfur compounds in the reaction system were required to increase the selectivity of hydrogenation when butadiene content in C4 fraction was relatively high (>1.0%).(2) It was found to be effective that presulfiding of the catalyst by hydrogen sulfide was carried out under low temperature in order to gain high hydrogenation selectivity.(3) Complete removal of butadiene without n-butenes loss was achieved from the studies on the reaction conditions. Activity and selectivity of the catalyst were preserved constantly during long run test.(4) Isomerization of 1-butene accompanied with hydrogenation was retarded by the presence of butadiene. Complete isomerization of 1-butene to 2-butene needed more severe conditions than complete removal of butadiene hydrogenation.(5) Palladium-alumina catalyst sulfided by hydrogen sulfide showed relatively strong resistance against the poison. In the presence of some gaseous inorganic compounds such as CO, Cl2, COCl2, N2O, N2O3, and SO2, selectivity of the hydrogenation increased. Moreover, CO completely depressed the isomerization of 1-butene.

Study on the Selective Hydrogenation of Butadiene in C&lt;sub&gt;4&lt;/sub&gt;-Hydrocarbon Fraction (Part 3)

Selective hydrogenation of butadiene to prepare 1-butene in a good yield has been studied over several group VIII metal catalysts in the presence of carbon monoxide. The following results were obtained.(1) In the presence of carbon monoxide, the selectivities of butadiene hydrogenation to n-butenes were kept nearly 100% until high conversion of butadiene over the various metal catalysts.(2) The selectivities of 1-butene and the trans-2-butene/cis-2-butene ratios did not change with the variation of the butadiene conversion over various metal catalysts and the selectivities of 1-butene over these catalysts were rebresented in the following order: Pt>Ir>Ph∼Ru>Pd>Ni and the order of trans-2-butene/cis-2-butene ratios were Pd>>Ir>Ni>Ru∼Ir>Pt. It was considered that 1-butene and 2-butenes were formed only by 1.2- or 1.4-addition of H2 on butadiene and the isomerization of 1-butene to 2-butenes did not proceed until butadiene disappeared.(3) Platinum-alumina catalyst showed very high 1-butene selectivity but resulted 1-butene was isomerized to 2-butenes when the butadiene conversion exceeded 90%. On the other hand, palladium-alumina catalyst showed somewhat lower 1-butene selectivity but no isomerization was observed. As a result, 1-butene could be produced in a good yield from butadiene using platinum-alumina catalyst followed by palladium-alumina catalyst in the presence of carbon monoxide in H2.