Pd-Pt Catalysts Research Articles

Decomposition of Hydrogen Peroxide using Chemical and Catalytic Methods: A Reactor-based Approach

A feasible catalytic reactor for oxygen evolution has been proposed, which could complement the current methods of O2 evolution efficiently and ensure the availability of pure oxygen on a wider scale. Several chemicals, such as NaI, MnO2, NiSO4, etc. can generally decompose hydrogen peroxide by producing oxygen as a product via chemical reactions. Meanwhile, the Pt-Pd catalyst efficiently catalyzes hydrogen peroxide decomposition reactions and generates pure oxygen without any unfriendly species. The excellence of the bi-metallic catalyst has been validated by the evaluation of turnover number (TON) and turnover frequency (TOF). Implementing the knowledge of chemical reactions and heterogenous catalysis, the proposed catalytic reactor could be helpful for generating a continuous flow of oxygen. Surely, the oxygen produced in this process is higher in amount compared to the oxygen present in the atmosphere at ambient conditions which might facilitate the breathing support for critically ill patients.

Chain-like PtPd nanoparticles with a long-time stability as an efficient electrocatalyst for alcohols oxidation reaction

In this study, chain-like PtPd/PVA catalysts were synthesized by a two-step hydrothermal method with the assistance of polyvinyl alcohol as a green reducing agent, structure guiding agent, dispersing agent, and binder. Among all the catalysts, Pt1Pd5/PVA catalyst shows the highest mass activity (3774.2 mA mgpt−1) for methanol oxidation reaction. Also, the residual activity of Pt1Pd5/PVA catalyst after chronoamperometry (CA) test of 28 h is close to that of commercial Pt/C after CA test of 5000 s. The excellent electrocatalytic activity of Pt1Pd5/PVA catalyst is mainly attributed to the synergistic effect between Pt and Pd. This can optimize the surface electronic structure and reduce the adsorption of CO-like species over the Pt surface. Besides, the unique chain network structure of PtPd forms a conductive network of self-conducting electrons. At the same time, a large amount of PVA causes an ultra-long stability through the coating of PtPd catalyst by PVA and the interaction with PVA and PtPd. This work contributes a facile and clean method for the synthesis of stable and efficient precious metal alloy catalysts for alcohols oxidation reaction.

Pt-Pd Bimetallic Nanocomposites Catalyst Formed on Graphene Surface: Preparation and high-performance for Methanol Electro-Oxidation

Pt-Pd Bimetallic Nanocomposites Catalyst Formed on Graphene Surface: Preparation and high-performance for Methanol Electro-Oxidation

Pt-Catalyzed D-Glucose Oxidation Reactions for Glucose Fuel Cells

The Pt-catalyzed D-glucose oxidation reaction in neutral electrolytes was investigated for implantable power applications. A reaction mechanism involving two possible oxidation pathways, namely direct and OHads-mediated oxidation, was proposed based on the mass change during electrochemical measurement. PtPd and Pt2Pd were synthesized as anodic catalysts by a solvothermal method, and single-chamber glucose-air fuel cells using a neutral aqueous electrolyte were prototyped successfully. Higher fuel cell performance was achieved with the PtPd catalyst, with a maximum power density of 27.6 μW cm−2 and open-circuit voltage of 0.616 V. Collectively, the present study contributes to maximize the performance of glucose fuel cells.

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment.

Enhanced performance of supported Pd-Pt bimetallic catalysts prepared by modified electroless deposition for butane dehydrogenation

The alumina supported Pd-Pt based bimetallic catalysts were prepared by modified electroless deposition and evaluated for butane dehydrogenation. The bimetallic Pd-Pt catalysts exhibited superior performance compared to that of monometallic catalysts. The superior performance may be attributed to strong synergistic interaction between metals, stronger metal-support interaction and lower acidity. The higher activity of alloyed Pd-Pt metal resulted in higher conversion for bimetallic catalysts. The lower acidity resulted in higher butene selectivity and stability for bimetallic catalysts by minimizing cracking and secondary reactions. The co-deposited catalyst with more uniform distribution of Pd and Pt metals showed better performance than bimetallic catalysts prepared by sequential deposition. Co-deposited Pd-Pt/Al catalyst showed the highest butane conversion (50 %), butene yield (42 %) and stability. The reported yield is much higher than many reported values for Pt or Pd based catalysts. The co-deposited Pd-Pt/Al catalyst also exhibited better dehydrogenation performance in comparison to corresponding co-impregnated bimetallic catalyst.

Ethylene glycol oxidation on carbon supported binary PtM (M = Rh, Pd an Ni) electrocatalysts in alkaline media

Abstract In this work we prepared binary Pt-based electrocatalysts supported on carbon with a 80:20 (Pt:M) atomic ratio (where M = Rh, Pd and Ni) and tested their activity for the ethylene glycol oxidation reaction (EGOR) in alkaline media. Pt90Pd10/C showed the highest catalytic activity for the EGOR. Then, to estimate the optimum Pd content for the EGOR, a new series of PtPd catalysts within a wide range of compositions was synthesized and tested. The electroactivity is dependent on the composition of PtPd and reaches a maximum at 32 at.% Palladium. In situ FTIR results suggest the presence of Pd increases the production of glycolate, while hinders the formation of carbonate. This inhibition, in turn, seems to be dependent on a previous scission of the molecules. Hence, compositions richer in Pd are more tolerant to surface poisoning because the production of fragments possessing a single carbon atom (such as CO) is hindered over these surfaces.

A modeling and experimental study on hydrothermal aging deactivation of NO oxidation activity on Pt-Pd catalyst

A state-of-the-art Pt-Pd catalyst was hydrothermally treated at different conditions to investigate hydrothermal stability of NO oxidation. NO oxidation reactor data was collected on catalysts that have been hydrothermally treated at temperatures ranging from 550 °C until 1100 °C. NO oxidation activity was observed to decrease with increase in aging duration at all the aging temperatures. A global kinetic model of NO oxidation was used to estimate the change in NO oxidation rate when subjected to different hydro-thermal aging conditions. Model estimated normalized rates at multiple hydro-thermal aging conditions were used to develop a hydro-thermal aging model of NO oxidation. A deactivation Model with Residual Activity (DMRA) was developed to capture the impact of hydrothermal aging temperature and duration on NO oxidation activity. A global kinetic model that accounts for change in PGM oxidation state during NO oxidation has also been presented.

Ambient Temperature CO Oxidation Using Palladium–Platinum Bimetallic Catalysts Supported on Tin Oxide/Alumina

A series of Pt-based catalysts were synthesised and investigated for ambient temperature CO oxidation with the aim to increase catalytic activity and improve moisture resistance through support modification. Initially, bimetallic PtPd catalysts supported on alumina were found to exhibit superior catalytic activity compared with their monometallic counterparts for the reaction. Following an investigation into the effect of Pt/Pd ratio, a composition of 0.1% Pt/0.4% Pd was selected for further studies. Following this, SnO2/Al2O3 supports were synthesised from a variety of tin oxide sources. Catalytic activity was improved using sodium stannate and tin oxalate precursors compared with a traditional tin oxide slurry. Catalytic activity versus tin concentration was found to vary significantly across the three precursors, which was subsequently investigated by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX).

The Pt-Pd alloy catalyst and enhanced catalytic activity for diesel oxidation

By use of a Pt-Pd alloy colloid solution, a Pt(1.0 wt%)-Pd(0.5 wt%) alloy catalyst was prepared on SiO2 support, and the supported Pt-Pd nanoparticles were verified to be highly alloyed and finely dispersed by energy dispersive X-ray spectroscopy (EDS), scanning transmission electron microscope (STEM), and CO adsorption. Under simulated diesel exhaust atmosphere, this Pt-Pd alloy catalyst exhibited a higher catalytic activity than the conventional Pt-Pd catalyst prepared by use of the common Pt and Pd precursors of Pt(NH3)2(NO2)2 and Pd(NO3)2 solutions. The characterization results of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of oxygen (TPD-O2) revealed that the Pt and Pd atoms of the Pt-Pd alloy catalyst were apt to be more metallic state, and the O2 adsorption and activation were facilitated significantly. Even at low temperature, there are more activated oxygen species available, and the surface of the Pt-Pd alloy catalyst gets more frequently refreshed for subsequent adsorption and activation for the CO and C3H6 reactants. The above effects resulted from the Pt-Pd alloying together with the high Pt-Pd dispersion of the supported Pt-Pd particles highly promoted the catalytic activity of the Pt-Pd alloy catalyst for diesel oxidation.

Increasing the Size-Selectivity in Laser-Based g/h Liquid Flow Synthesis of Pt and PtPd Nanoparticles for CO and NO Oxidation in Industrial Automotive Exhaust Gas Treatment Benchmarking.

PtPd catalysts are state-of-the-art for automotive diesel exhaust gas treatment. Although wet-chemical preparation of PtPd nanoparticles below 3 nm and kg-scale synthesis of supported PtPd/Al2O3 are already established, the partial segregation of the bimetallic nanoparticles remains an issue that adversely affects catalytic performance. As a promising alternative, laser-based catalyst preparation allows the continuous synthesis of surfactant-free, solid-solution alloy nanoparticles at the g/h-scale. However, the required productivity of the catalytically relevant size fraction <10 nm has yet to be met. In this work, by optimization of ablation and fragmentation conditions, the continuous flow synthesis of nanoparticles with a productivity of the catalytically relevant size fraction <10 nm of >1 g/h is presented via an in-process size tuning strategy. After the laser-based preparation of hectoliters of colloid and more than 2 kg of PtPd/Al2O3 wash coat, the laser-generated catalysts were benchmarked against an industry-relevant reference catalyst. The conversion of CO by laser-generated catalysts was found to be equivalent to the reference, while improved activity during NO oxidation was achieved. Finally, the present study validates that laser-generated catalysts meet the size and productivity requirements for industrial standard operating procedures. Hence, laser-based catalyst synthesis appears to be a promising alternative to chemical-based preparation of alloy nanoparticles for developing industrial catalysts, such as those needed in the treatment of exhaust gases.

Aqueous phase reforming of alcohols over a bimetallic Pt-Pd catalyst in the presence of formic acid

Aqueous phase reforming (APR) of four polyols (ethylene glycol, glycerol, erythritol and sorbitol) was studied over a bimetallic Pt/Pd catalyst supported on mesoporous carbon in the temperature range between 200 °C and 225 °C. Addition of formic acid was studied for a potential industrial application, which involves upstream reactive extraction of hemicelluloses.APR of all polyols resulted in high levels of hydrogen production, which could be even improved by a temperature increase and addition of formic acid. Selectivity to alkanes was similar for most of the polyols with methane and ethane being the most prominent product among alkanes.The liquid phase displayed presence of significant amounts of methanol and propane diols. Analysis of the liquid products suggests a strong interrelation between the reaction pathways in APR of tested polyols.

DFT study of methane catalytic combustion on Pd-based diatomic catalysts

The processes of methane combustion on three Pd-based diatomic catalysts (Pd2, PdPt and PdNi) are investigated by using density functional theory (DFT) at the B3LYP/6-311++G(d,p)+SDD//B3LYP/6-311G(d,p)+LANL2DZ level. The optimized geometric structures, activation energy (Ea ), and reaction rate constant (k) of methane dehydrogenation and oxidation on Pd2, PdPt and PdNi are compared. The main reaction path for methane combustion on catalyst Pd2 is CH4→CH3→CH2→CHOH→CHO→CO→CO2. However, the main reaction paths on catalyst PdPt and PdNi are the same: CH4→CH3→CH2OH→CHOH→CHO→CO→CO2. The rate-determining steps (RDS) on catalyst Pd2 and PdPt are the same: CHOH→CHO, while the step of CH3→CH2OH is the RDS on PdNi. Further analysis shows that the catalytic activity followed the order of PdPt (k = 1.0639×104 s−1) > Pd2 (k = 1.7281×102 s−1) > PdNi (k = 1.9235×10 s−1). Thus, PdPt catalyst exhibits better performance than the other two catalysts in the methane catalytic combustion.

Mechanistic effects of Water on Carbon monoxide and propylene oxidation on platinum and palladium bimetallic catalysts

Low temperature combustion (LTC) diesel engines are more fuel efficient and have coincident lower temperature exhaust gas and higher CO and hydrocarbon exhaust gas concentrations than today’s standard diesel engine. To meet regulations, diesel oxidation catalysts (DOCs) will need to be improved and optimized to handle these higher CO and hydrocarbon concentrations emitted and the simultaneous lower exhaust temperatures. Pt-Pd bimetallic catalysts are often used as oxidation catalysts. Here, the mechanistic effects of water on CO and C3H6 oxidation were studied over model monometallic Pt and Pd catalysts, and a bimetallic 1:1 Pt-Pd/ γ-Al2O3 catalyst. Water in the reaction mixture improved CO oxidation light-off for the monometallic Pd and Pt-Pd catalysts and had a negative impact on light-off over the monometallic Pt catalyst. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that more CO adsorbed on the Pd and Pt-Pd catalysts when water was present, particularly at the particle/support interface, while the opposite occurred on the Pt catalyst. For C3H6 oxidation, water in the reaction showed a negative impact on the light-off temperature for the Pd catalyst and a positive effect for the Pt catalyst. The Pt-Pd catalyst showed intermediate light-off behavior between the two monometallic catalysts. In terms of selectivity, slightly more CO and acetic acid were formed over the Pd and Pt-Pd catalysts when water was in the reaction mixture, while less CO was formed over the Pt catalyst, but overall, the selectivity towards certain partial oxidation products was not greatly affected with the addition of water to the reaction mixture.

Correlation of the ratio of metallic to oxide species with activity of PdPt catalysts for methane oxidation

Activity of catalysts increase linearly with increasing ratio of Pd/Pt bimetallic to oxide species as observed in XRD.

Effect of Pt pre-sintering on the durability of PtPd/Al2O3 catalysts for CH4 oxidation

Unburned CH4 is a primary component of natural gas and its contribution to the greenhouse effect is 20 times that of CO2. Durable oxidation catalysts are critical for developing natural gas vehicles (NGV). Pd-based catalysts with Pt promotion have been widely used for CH4 oxidation due to their activity, durability, and tolerance in H2O and sulfur. However, significant drawbacks including poor durability and ineffective synthesis protocols related to the Pt:Pd ratio, exist. Here, we achieve significant improvements in the activity and durability of PtPd bimetallic catalysts for CH4 oxidation by simply pre-sintering the Pt particles before the addition of Pd. Energy dispersive X-ray spectroscopy coupled with scanning transmission electron microscopy, X-ray diffraction, and diffuse reflectance infrared Fourier-transform spectroscopy studies demonstrate that sequential impregnation of Pd after pre-sintering of Pt led to a segregated PdO layer on top of the pre-sintered metallic clusters, while the co-impregnated PtPd catalysts (without pre-sintering of Pt) exhibited homogeneous distribution of Pt and Pd. Re-oxidation experiments after regeneration by fuel-rich combustion, demonstrated the rapid Pd to PdO re-oxidation behavior for the pre-sintered catalysts compared to that for the co-impregnated catalysts, which we thought important for long-term durability due to the facile catalytic cycle needed for CH4 oxidation. All results suggest that the PdO surface layer on top of the Pt clusters is critical for long-term durability of CH4 oxidation; herein, important insight on the critical nature of the molecular level design of bimetallic clusters towards the development of more durable Pd-based catalysts for CH4 oxidation, is provided.

Characterization of Highly Active Al2O3-TiO2 Supported Pt and Pd Catalysts for Hydrodechlorination of 1,2-Dichloroethane

Abstract Al2O3-TiO2 (AT) mixed oxide with atomic ratio Al/Ti = 25 and Al2O3 (A) supports were prepared by the sol-gel method and impregnated to obtain monometallic Pd and Pt (1 wt % of metal), and bimetallic PdPt (Pd/Pt = 4) catalysts. These catalysts were tested in the gas-phase hydrodechlorination of 1,2 dichloroethane. The materials were characterized by nitrogen physisorption, X-ray diffraction analysis (XRD), temperature-programmed reduction (TPR) and high-resolution transmission microscopy (HRTEM). AT support showed a BET area (422 m2/g), slightly higher than A(374 m2/g). The specific activity for the AT supported catalysts was higher than that for the A supported catalysts. The order of activity for the AT supported catalysts was as follows: Pd&gt; PdPt&gt; Pt and in terms of selectivity towards non-chlorinated compounds the order was PdPt&gt; Pd&gt; Pt. The differences in the activities and the selectivities can be explained by the presence of different species of Pd in the supported catalysts.

Theoretical study of the oxidation of formic acid on a PtPd(111) surface

By performing density functional theory calculations, the adsorption configurations of formic acid and possible reaction pathway for HCOOH oxidation on PtPd(111) surface are located. Results show that CO2 is preferentially formed as the main product of the catalytic oxidation of formic acid. The formation of CO on the pure Pd surface could not possibly occur during formic acid decomposition on the PtPd(111) surface owing to the high reaction barrier. Therefore, no poisoning of catalyst would occur on the PtPd(111) surface. Our results indicate that the significantly increased catalytic activity of bimetallic PtPd catalyst towards HCOOH oxidation should be attributed to the reduction in poisoning by CO.

A Novel Fabricating Process of Catalytic Gas Sensor Based on Droplet Generating Technology.

Catalytic gas sensors are widely used for measuring concentrations of combustible gases to prevent explosive accidents in industrial and domestic environments. The typical structure of the sensitive element of the sensor consists of carrier and catalyst materials, which are in and around a platinum coil. However, the size of the platinum coil is micron-grade and typically has a cylindrical shape. It is extremely difficult to control the amount of carrier and catalyst materials and to fulfill the inner cavity of the coil, which adds to the irreproducibility and uncertainty of the sensor performance. To solve this problem, this paper presents a new method which uses a drop-on-demand droplet generator to add the carrier and catalytic materials into the platinum coil and fabricate the micropellistor. The materials in this article include finely dispersed Al2O3 suspension and platinum palladium (Pd-Pt) catalyst. The size of the micropellistor with carrier material can be controlled by the number of the suspension droplets, while the amount of Pd-Pt catalyst can be controlled by the number of catalyst droplets. A bridge circuit is used to obtain the output signal of the gas sensors. The original signals of the micropellistor at 140 mV and 80 mV remain after aging treatment. The sensitivity and power consumption of the pellistor are 32 mV/% CH4 and 120 mW, respectively.

Experimental and theoretical investigation of oxidative methane activation on Pd-Pt catalysts.

Density functional theory (DFT) and measurements of rate are used to provide evidence for the rate determining step (RDS) and requirements of the active site for CH4 combustion on Pd–Pt bimetallic catalysts in five different distinct kinetic regimes. These five regimes exhibit different rate equations for methane combustion due to the reaction rate constants and diverse dominant adsorbed species for these different kinetically relevant steps. Oxygen chemical potential at the Pd–Pt surface was replaced by oxygen pressure, reflecting the kinetic coupling between C–H and O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O bond cleavage steps. C–H bond cleavage occurs on different active sites in five of these kinetic regimes, evolving from vacancy–vacancy (*–*) to oxygen–vacancy (O*–*), oxygen–oxygen (O*–O*) site pairs, monolayer Pd–O, and ultimately to oxide bulk with Pd–O site pairs as the oxygen chemical potential increases. It is easier to form a metallic surface at low oxygen pressure, implying minimal O* coverage. The sole kinetically relevant step on uncovered Pd–Pt surfaces for methane combustion is OO bond cleavage. The supply of oxygen is obviously more important than the supply of methane in regime (I). As vacancies become less available on metallic surfaces, C–H bond cleavage occurs via O*–* paired sites, the energy barrier of which is much higher than that on uncovered Pd–Pt surfaces. In this regime (II), OO bond cleavage is still an irreversible process because O* will be consumed by the rapidly formed products of methane dissociation. For the oxygen saturated surfaces in regime (III), C–H bond cleavage occurs on two adjacent adsorbed oxygens that form OH and weak CH3–O bond interactions, resulting in a low activity for methane combustion. On the oxidation surfaces (IV and V), exposed metal atoms and their adjacent exposed lattice oxygen were the active sites, leading to a large decrease in C–H bond cleavage energy barrier, deduced from both experiment and theory. The increase of the metallic oxide thickness (increase of oxygen potential) increases the methane combustion turnover rates on Pd–Pt catalysts.