Palladium On Activated Carbon Research Articles

Investigating the Catalytic Deactivation of a Pd Catalyst during the Continuous Hydrogenation of CO2 into Formate Using a Trickle-Bed Reactor

The practical application of formic acid production through the hydrogenation of CO2 has garnered significant attention in efforts to tackle the challenges associated with (1) achieving net-zero production of formic acid as a chemical feedstock and (2) improving hydrogen storage and transport. This study focuses on demonstrating the continuous operation of a trickle bed reactor for converting CO2 into formate using palladium on activated carbon (Pd/AC). Optimal temperature conditions were investigated through a dynamic operation for 24 h, achieving the maximum productivity of 2140 mmolFA·gPdsurf.−1·h−1 at 150 °C and 8 MPa, with an H2/CO2 ratio of 1:1; however, catalyst deactivation was observed in the process. Stability tests performed under continuous operation at 120 °C and 8 MPa with an H2/CO2 ratio of 1:1 indicated a gradual decline in productivity, culminating in a 20% reduction after 20 h. A comprehensive analysis comparing fresh and spent catalysts revealed that the diminished catalytic activity at elevated temperatures was attributed to the partial sintering and leaching of Pd nanoparticles during the hydrogenation process. These findings offer insights for the future development of novel Pd-based catalyst systems suitable for continuous hydrogenation processes.

Experimental study of catalytic hydro-dechlorination (HDC) of Aroclor 1232

Polychlorinated biphenyls (PCBs) is a group of persistent organic pollutants that still requires remediation and reduction long after the production is discontinued. Aroclor 1232 is a commercial PCB mixture that has been much less studied. To address this void, this paper presented catalytic hydro-dechlorination (HDC) of Aroclor 1232 using palladium on activated carbon (Pd/AC) at atmospheric pressure. Experimental variables studied including three mild temperatures, 22.5 °C, 50 °C, and 80 °C, and four different co-catalyst loadings. This batch of Aroclor 1232 constituted of more than 83% of mono-, di-, and tri-, chlorinated biphenyls (CB), in addition to biphenyl, tetra- and penta CBs. HDC efficiency increased with temperature, and reached 99.9% within 4 h of reaction at 80 °C. HDC efficiency also increased with co-catalyst loading. HDC efficiencies followed the trend of para > meta > ortho positions among isomers. The increase of temperature and Et3N dosage are especially effective in dechlorination at ortho and meta positions. The apparent activation energy of Aroclor 1232 HDC was estimated as 25.57 kJ/mol based on pseudo-first order assumption, indicating that the reaction may be diffusion limited. Given the modest reaction conditions used, the HDC of Aroclor 1232 can potentially be a low-cost process.

Palladium doped with boron and phosphorus on activated carbon: a high-performance nanocatalyst for the hydrogenation of alkenes

Fabrication of high-performance palladium on activated carbon (Pd/AC) nanocatalysts for hydrogenation of alkenes to reduce the cost of reaction products has always been of interest to researchers and industries. Herein, the purpose was the step-by-step investigation of the simple precipitation-reduction method to determine the best chemicals usable in producing the high-performance 10%Pd/AC nanocatalyst for the hydrogenation of alkenes. Hence, different types of carbon supports, alkaline agents, and reducing agents were selected for this purpose. Catalytic hydrogenation of cinnamic acid to hydrocinnamic acid was used as a well-known standard test for evaluating the activity of the nanocatalysts. The AC prepared by pine wood, H2PdCl4, KHCO3, and NaBH4/NaH2PO2 were the most suitable materials for producing high-performance Pd/AC using the mentioned method. It was specified that activity is increased with the lower amount of oxygenated acidic functional groups on the AC, greater cation radius of the alkaline agent, weaker alkaline agent, and higher reduction power of the reducing agent. NaH2PO2 and especially NaBH4 increase the activity more than other reducing agents because of their high reduction power and adding phosphorus (P) and boron (B) to Pd, respectively. Three nanocatalysts with the most activity were chosen for more investigations by different analyses. The results of these analyses were according to the procedure obtained for their catalytic activity. The reusability test of chosen nanocatalysts indicated that the stability of Pd/AC is increased by doping the Pd with B and especially P. According to the obtained results, Pd nanocatalyst doped with both P and B is strongly recommended for application in alkenes hydrogenation.

Catalytic upgradation of bio-oil over metal supported activated carbon catalysts in sub-supercritical ethanol

The bio-oil was upgraded in sub-supercritical ethanol using metal supported platinum on activated carbon (Pt/AC) and palladium on activated carbon (Pd/AC) as catalysts. The supercritical upgrading process revealed more effective process compared to the subcritical conditions. Esterification during catalytic upgrading of bio-oil remained prominent which facilitates the conversion of acids present in bio-oil into esters in sub-supercritical ethanol. In addition, heavy compounds of crude bio-oil cracked into lighter compounds in the presence of catalysts. Furthermore, the changes in the upgraded bio-oil relative to crude bio-oil was extensively investigated through higher heating value (HHV), elemental analysis, solution pH, chemical composition (GC-MS), chemical functional groups (FTIR), and 13C and 1H nuclear magnetic resonance spectroscopy (NMR). The chemical composition analysis showed a significant decrease in acid fractions in sub-supercritical upgrading process, hence the solution pH varied from 2.5 in bio-oil to 5.3 after supercritical reaction. The HHV of bio-oil increased from 28.55 to 36.4 MJ/kg. This research has shown that crude bio-oil can be efficiently upgraded with carbon-supported metal catalysts in a sub-supercritical upgrading process.

MEA Preparation for Direct Formate/Formic Acid Fuel Cell-Comparison of Palladium Black and Palladium Supported on Activated Carbon Performance on Power Generation in Passive Fuel Cell.

Membrane electrode assemblies (MEAs) with palladium catalysts were successfully prepared by using a home-made manual pressing system with Nafion glue application that contributed to a decrease of additional energy consumption. The catalyst coated membranes were prepared with supported palladium on activated carbon (PdC) and unsupported palladium black (PdB) for comparison. The performance of passive, air breathing, functioning under ambient conditions and with low concentration (1 M) formate/formic acid fuel cell was evaluated. Based on polarization curves, the best result was obtained with carbon supported catalyst and HCOOK fuel, achieving 21.01 mW/mgPd. Still, constant current discharge with PdC showed an energy generation efficiency of 14% with HCOOH over 3% with HCOOK caused by lower potassium ion conductivity and its permeability through the proton exchange membrane. The faradic efficiency of conversion in the cell is equal to the overall energy efficiency and makes the cell self-sufficient.

Analysis of the deactivation of Pd, Pt and Rh on activated carbon catalysts in the hydrodechlorination of the MCPA herbicide

The deactivation of a palladium on activated carbon (Pd/AC) catalyst in the hydrodechlorination (HDC) of the organochlorinated herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in water under ambient-like conditions has been studied. The loss of activity is attributed to the accumulation of organic species involved in the reaction on the catalyst surface. The analysis of the fresh and used catalysts indicated the possibility of regeneration by thermal or washing (water, NaOH solutions) treatments. Bimetallic catalysts, Pd-Rh/AC and Pd-Pt/AC, showed lower activity than the Pd/AC one but higher stability (slower deactivation). A Pd catalyst supported on an activated carbon modified upon oxidation (Pd/ACOX) exhibited higher activity and stability which can be due to the high concentration of surface oxygen groups that reduced the uptake of fouling species.

Stabilization of bio-oils using low temperature, low pressure hydrogenation

The superficial similarities between petroleum and bio-oil have encouraged efforts to employ petroleum hydroprocessing in the upgrading of bio-oil. Any facile comparison is overshadowed by the fact that petroleum consists of non-polar hydrocarbons that are relatively stable, requiring elevated temperatures and pressures to encourage chemical transformations, whereas bio-oil consists of oxygenated organic compounds whose high degree of functionality makes them chemically reactive even at low temperatures and pressures. Lignin-derived phenolic compounds readily polymerize and dehydrate to coke when hydroprocessed, resulting in low carbon yields of fuel range molecules and catalyst deactivation. In light of the limitations of conventional hydroprocessing, we explore low-temperature, low-pressure (LTLP) hydrogenation of pyrolysis-derived phenolics over 10% palladium on activated carbon (Pd/C) at 21°C and 1bar pressure as a way to produce stabilized bio-oil at high yields.

Deactivation of a Pd/AC catalyst in the hydrodechlorination of chlorinated herbicides

This work analyses the stability of a palladium on activated carbon (Pd/AC) catalyst in the ambient-like conditions hydrodechlorination (HDC) of the organochlorinated herbicides 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4-dichlorophenoxyacetic acid (2,4-D) as well as 2,4-dichlorophenol (2,4-DCP), a precursor in the synthesis of the second. Continuous long term experiments (100h time on stream) were performed at mild operating conditions (30°C, 1atm). The composition of the reaction effluents was analyzed and their ecotoxicity (Microtox) measured. In all cases, a significant decrease of ecotoxicity was observed due to the high dechlorination achieved. The Pd/AC catalyst maintained a constant activity along the HDC of 2,4-DCP, while it suffered an important deactivation in the HDC of 2,4-D and MCPA. From characterization of the fresh and used catalyst the adsorption/deposition of reaction byproducts on the active sites can be recognized as the main cause of deactivation. The use of activated carbon as support reduces the negative effect that the released chloride ions usually provoke on other HDC catalysts.

Palladium‐catalyzed carbonylation of quaternary ammonium halides to tertiary amides

Catalytic carbonylation of quaternary ammonium salts under anhydrous conditions was investigated using palladium catalyst. The carbonylation of tetramethylammonium iodide was chosen as a model reaction and studied systematically. Ligand‐free PdCl2 showed efficient catalytic performance for this transformation. A palladium catalyst loading as low as 0.05 mol% was sufficient for high yield (96.9%) of N,N‐dimethylacetamide, corresponding to a turnover frequency of 242 h−1. Under optimum conditions, several other quaternary ammonium halides were also carbonylated to corresponding tertiary amides in moderate to excellent yields. The catalytic activity of commercial palladium on activated carbon (Pd/C) catalyst was also evaluated. The Pd/C catalyst exhibited high activity for this carbonylation reaction and could be recycled six times with a slight decrease in activity. Furthermore, mechanistic considerations concerning Pd‐catalyzed carbonylation of quaternary ammonium halides were also discussed. Copyright © 2014 John Wiley & Sons, Ltd.

An improved practical Pd/C‐catalyzed Sonogashira cross‐coupling reaction for the synthesis of liquid crystals of trans‐cyclohexyltolans

AbstractAn improved practical synthesis of liquid crystals of trans‐cyclohexyltolans by Sonogashira cross‐coupling reaction of 1‐iodo‐4‐(trans‐4‐alkylcyclohexyl)benzene with aromatic terminal alkynes in the presence of Pd/C (palladium on activated carbon) as low as 0.03 mol% of Pd and CuI (2 mol%) in a mixture solvent of acetone–water (5:2 in volume) is described. The liquid crystals could be obtained in high yields as a solid with excellent purity by simple filtration, and the filtrate could be reused several times while still retaining high catalytic activity. Copyright © 2010 John Wiley & Sons, Ltd.

Catalytic hydrothermal deoxygenation of palmitic acid

We herein report a new approach to convert fatty acids to hydrocarbons in near- or supercritical water. We tested several different metal salts, bases, and high-surface-area supported metal catalysts for activity toward deoxygenation of palmitic acid in a hydrothermal reaction medium. Two heterogeneous catalysts, 5% platinum on activated carbon (Pt/C) and 5% palladium on activated carbon (Pd/C), proved to be very effective for hydrothermal deoxygenation of palmitic acid. The reactions were done in water with no added H2. The catalysts can be reused without significant activity loss, and the selectivity was more than 90% toward pentadecane, the deoxygenation product. We examined the effect of the catalyst loading, reactant loading, batch holding time, and reaction temperature on the Pt/C-catalyzed deoxygenation rate. The results show that the reaction is first-order in palmitic acid, and the rate constants displayed Arrhenius behavior with an activation energy of 79 kJ mol−1.

Catalytic hydroconversion of tricaprylin and caprylic acid as model reaction for biofuel production from triglycerides

There is strong interest in the production of fuels from triglycerides of biological origin. In this work tricaprylin (TC) and caprylic acid (CA) were used as model compounds to study the catalytic hydroconversion process of triglycerides to acyclic aliphatic hydrocarbons. Supported metal and metal oxide catalysts, such as palladium on activated carbon (Pd/C), and promoted molybdena–alumina (Ni,Mo/γ-Al 2O 3) were used. The reaction was found to proceed in consecutive steps: hydrogenolysis (HYS) of TC to CA and propane, followed by hydrodeoxygenation (HDO) of the CA intermediate. The overall reaction rate was governed by the rate of the HDO reaction. Two distinct HDO routes were distinguished: (i) hydrodecabonylation and (ii) reduction of oxygen. Over Pd/C the prevailing reaction route of CA hydroconversion was the decarbonylation giving mainly C 7 alkane and CO, whereas the HDO over the Ni,Mo/γ-Al 2O 3 catalysts proceeded in consecutive H 2 addition and dehydration steps giving predominantly C 8 = alkenes, C 8 alkanes and water. In reaction route (ii) alcohol and traces of aldehyde were detected as acid-to-alkane intermediates. Results suggest that reaction route (i) passes through formic acid intermediate that, in the presence of H 2, rapidly decomposes to CO and H 2O.

Palladium/Carbon Catalyzed Hydrogen Transfer Reactions using Magnesium/Water as Hydrogen Donor

A new methodology is developed for the hydrogenation reaction using magnesium/water system, as hydrogen source under catalytic palladium on activated carbon (Pd/C). The method is highly efficient for the chemoselective reduction of wide range of unsaturated aldehydes and ketones. The process is also found to be suitable when we think about green chemistry for the eco-friendly hydro-dehalogenation of aromatics. From practical point of view this new methodology is the most attractive, efficient, economical and convenient approach towards industrially important reduction transformations. This report is intended to highlight the use of Mg/H2O system in these organic transformations which can be easily adopted in industrial scale for the bulk production of hydrogenation products.

A Practical Synthesis of Multifunctional Ketones Through the Fukuyama Coupling Reaction.

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A Practical Synthesis of Multifunctional Ketones through the Fukuyama Coupling Reaction

AbstractA highly efficient, robust and scalable protocol for the synthesis of multifunctional ketones through Fukuyama coupling, i.e., cross‐coupling of thiol esters with zinc reagents, has been developed. Treatment of thiol esters with alkylzinc iodides or dialkyl zincs in the presence of palladium on activated carbon (Pd/C) or palladium acetate [Pd(OAc)2] furnished the corresponding ketones in high yields. Evaluation of the properties‐activities relationship of the Pd/C‐catalyzed reaction has proven that oxidic Pd/C is much more potent than reduced Pd/C in the reaction of thiolactone 1a with zinc reagent 2a. Based on the dependence of the Pd/C‐catalyzed reaction on the nature of Pd/C in combination with the extent of the Pd leaching from Pd/C to the solution, a dual reaction mechanism for the Pd/C‐catalyzed Fukuyama coupling reaction, which includes heterogeneous and homogeneous catalytic cycles, was proposed. The marked reduction of the zinc reagents and the use of Pd(OAc)2 in much smaller amounts were achieved when zinc bromide was added. This supports a hypothesis where a shift of the Schlenk equilibrium from inactive dialkylzincs (R2Zn) to active organozinc species, such as alkylzinc halides (RZnX) and three‐coordinate species [(RZnX2)−⋅ (ZnX)+], and generation of the stabilized monomeric Pd complexes during the reaction, may facilitate the reaction.

Recent Advances in Pd/C-Catalyzed Coupling Reactions

A practical approach to multifunctional compounds through palladium on activated carbon (Pd/C)-catalyzed coupling reactions is described. A close correlation of the properties of the Pd/C with reaction efficiency has been observed and depends largely upon the type of reaction. A critical role of the activated carbon is to help palladium disperse sufficiently on the solid support to form the active palladium complex without aggregating to inactive palladium black. The use of Pd/C avoids contamination of the product with palladium and expedites recovery of the metal. The reactions are practical and have been applied to cost-effective large-scale production of multifunctional compounds for drug synthesis.

遷移金属触媒を用いたアルコールの環境調和型酸化反応

Recently reported oxidation process of alcohols using molecular oxygen as an oxidizing agent in the presence of catalytic amount of transition metals such as copper, ruthenium, palladium compounds will be reviewed. Oxidation of alcohols based on hydrogen transfer reaction between alcohols and simple olefins such as ethylene is also described. That is, some benzylic and allylic alcohols can be converted into the corresponding carbonyl compounds using a catalytic amount of palladium on activated carbon (Pd-C) under ethylene atmosphere. The combination of Pd (OAc) 2 and vinyl acetate also works efficiently. Selective oxidation of hydroxy groups on carbohydrates (D-glycals) and steroids as well as simpler systems has been achieved. These environmentally benign oxidation methods have potentialities to replace the conventional stoichiometric chromium and other metal oxides reagents.