Carbon-supported Pd Catalysts Research Articles

Voltammetric quantification of H:Pd ratio complicated by α↔β phase transition in PdHx: Electrodes with low Pd loadings

The Pd hydride (PdHx) is a typical system to study the fundamentals of solute intercalation and phase transformations or to determine the effect of strain on the rate of electrocatalytic reactions. A crucial methodological aspect, however, involves quantitatively determining the hydrogen-to-palladium atomic ratio (H:Pd) under experimental conditions where various incidental contributions to the total electrode charge are comparable to the charge spent for H adsorption/absorption and desorption. This is the case for electrodes with relatively low (dozens of μg/cm2) loadings of Pd on various porous supports, typically used to study the oxidation of small organic molecules or the reduction of oxygen in acidic or alkaline fuel cells. Ultra-low Pd loadings (often in the range of a few μg/cm2) are also typical for Pd nanoparticles on smooth supports, which are commonly considered as model systems for in situ structural studies of hydrogen sorption. To determine accurately the H content in Pd particles, we propose a technique based on analysis of charge disbalance at anodic and cathodic scans of a cyclic voltammogram, and also address the contribution of adsorbed H. To illustrate the possibilities and limitations of this technique, we present the voltametric study of thin electrodeposited Pd layers on glassy carbon and of a carbon-supported Pd catalyst.

Effect of I- ligand and surface oxygen-containing groups on catalytic activity and stability of activated carbon-supported Pd catalysts in acetylene dicarbonylation

The support and ligand play a crucial role in regulating the catalytic performance, selectivity, and stability of heterogeneous catalysis. Herein, activated carbon (AC) supported palladium (Pd) catalysts (2.0 wt%) were prepared by impregnation for acetylene dicarbonylation. The oxygen-containing groups on the surface of the AC support were modulated by nitric acid (HNO3) to investigate metal–support interactions on the catalytic performance and stability of the Pd/AC. The characterization of the chemical composition and structure of the supports and catalysts demonstrates that high concentrations of oxygen-containing groups on the surface of the carbon support lead to the fine dispersion of Pd nanoparticles. Notably, the finely dispersed Pd/AC70 catalyst exhibited good activity and stability for acetylene dicarbonylation under high-pressure CO conditions after several rounds of regeneration. Furthermore, operational parameters including the type of support, co-catalyst (KI), and reaction time and temperature were identified for their impact on the reaction. It was found that I- anions serve as a co-catalyst and can ligate with Pd species, thereby preventing the leaching of Pd and improving reaction selectivity. This study presents a straightforward and sustainable modulation strategy to improve the dispersion of active metals, as well as to prevent the leaching and sintering of these metals during high-pressure CO reactions.

Fabrication modulation of lignin-derived carbon nanosphere supported Pd nanoparticle via lignin fractionation for improved catalytic performance in vanillin hydrodeoxygenation

Nano-lignin presents great potential in advanced carbon materials preparation since it integrates the advantages of nanomaterials as well the preferable properties of lignin (e.g. high carbon content and highly aromatic structure). Herein, lignin-derived carbon nanosphere supported Pd catalysts (Pd@LCNS) were prepared via a two-step carbonization of Pd2+ adsorbed lignin nanospheres (LNS) and applied in vanillin hydrodeoxygenation. The effect lignin heterogeneity on the synthesis of Pd@LCNS as well as its catalytic performance was further investigated through the synthesis of Pd@LCNS using three lignin fractions with different molecular weight. The results showed that the three Pd@LCNSs exhibited significant differences in the morphology of both carbon support and Pd nanoparticles. Pd@LCNS-3 prepared from high molecular weight lignin fraction (L-3) presented stable carbon nanosphere support with the smallest particle size (∼150 nm) and the highest Pd loading amount (3.78 %) with the smallest Pd NPs size (∼1.6 nm). Therefore, Pd@LCNS-3 displayed superior catalytic activity for vanillin hydrodeoxygenation (99.34 % of vanillin conversion and 99.47 % of 2-methoxy-4-methylphenol selectivity) at 90 °C without H2. Consequently, this work provides a sustainable strategy to prepare uniformly dispersed lignin-based carbon-supported Pd catalyst using high molecular weight lignin as the feedstock and further demonstrate its superior applicability in the selective transfer hydrogenation of vanillin.

Evaluation of hardwood or softwood bark biomass as feed materials for aqueous-phase reforming gasification process

In the present study, pine (Pinus brutia) and poplar (Populus alba) tree barks, softwood and hardwood representative biomass were evaluated for production of gas biofuel, hydrogen by aqueous-phase reforming. The proximate composition, elemental composition, higher heating values (HHVs), proximate thermogravimetric and differential thermogravimetric analysis (TGA/DTG), fourier transform infrared (FT-IR), and volatile composition of these biomass materials were determined and their effect on gasification performance of the softwood and hardwood biomass were evaluated. Gasification was performed by aqueous-phase reforming of solubilized liquid fraction of the biomass materials in presence of carbon-supported Pd catalyst which was synthesized in the present study. Softwood contained significantly higher levels of ash and volatile matter, with lower hemicellulose but higher lignin content. Gasification results showed that softwood produced slightly higher amounts of hydrogen with significantly lower carbon monoxide compared to hardwood. Although solid hardwood bark composition was expected to produce more gaseous products, the results observed were opposite. The dissolution of biomass in pressured hot water prior to gasification resulted in a more dilute hydrolysate in softwood compared to hardwood, positively influencing the gasification performance. Despite of many advantages of the aqueous-phase reforming (APR) gasification process used in the present study, the process still needs to be improved further to make the process more economical. To increase the advantage of this process, new catalysts that are more robust and active and have high stability in organic-rich APR conditions should be developed.

Effect of Supporting Pd Nanoparticles on WOx Nanorods on Their Stability and Catalytic Activity Towards the Electrochemical Oxidation of Concentrated Formic Acid

Direct formic acid fuel cells (DFAFC) are considered one of the most promising fuel cells to penetrate the market due to their desired and unique properties. Formic acid (FA) could be easily produced from different sources (especially biomass) and is non-toxic. The FA-based fuel cell has a high open circuit potential in comparison to methanol and Ethanol1, high energy conversion efficiency, and fast kinetics. However, the major drawback that affects using DFAFCs is the catalysts' stability and reaction intermediates' poisoning effect, especially at high concentrations of FA.FA has a dual pathway mechanism: either the simple and desired pathway of direct oxidation to CO2 2 or the unfavorable indirect oxidation to poisonous CO-like species that strongly adsorb on the catalyst surface, deactivating it,3 before it is hardly oxidized in a second step to give CO2. Therefore, the catalyst should be designed to direct the reaction towards the direct pathway and facilitate the poisoning species removal. The most active catalyst for FA oxidation in acidic media is palladium4 but it is highly susceptible to CO poisoning, especially as the FA concentration increases due to the high contribution of the indirect pathway. In addition, palladium nanoparticles supported on carbon material are known to suffer from dissolution in the acidic media making the electrode unstable for long-term application.5 In this presentation, the synthesis of nonstoichiometric WOx nanorods using hydrothermal methods will be reported. The Pd nanoparticles are synthesized and loaded on the WOx nanorods using ethanol as both a solvent and a reducing agent to produce a surfactant-free Pd surface. The synthesized materials are evaluated using XRD, TEM, FT-IR, EDS, and XPS. The effect of WOx nanorods as catalyst support on Pd nanoparticles activity and stability towards the oxidation of different concentrations (1-4 M) of FA in acidic media are evaluated using cyclic voltammetry (CV) and chronopotentiometry (CP), and compared with that of carbon-supported Pd catalyst. The Pd behavior in both cases will be correlated to its chemical and physical properties and thoroughly discussed.

Inelastic neutron scattering study of the H2 interaction with carbon-supported Pt and Pd catalysts

Carbon-supported Pt and Pd catalysts are largely employed as heterogeneous catalysts for hydrogenation reactions. Albeit their routine use in industry, many details about their interaction with H2 are still not completely understood. In this article, we propose a detailed investigation of the behavior in the presence of H2 of an activated carbon and of two catalysts obtained by depositing on it Pt and Pd nanoparticles by means of Inelastic Neutron Scattering (INS) spectroscopy. The high-quality INS spectra of the three samples were measured in absence and in presence of different amounts of H2, providing very detailed information about H2 physisorption on each system and about the nature of the metal hydrides formed upon hydrogenation of the catalysts. In addition, we were also able to obtain a direct observation of the occurrence of hydrogen spillover from the metal nanoparticles onto the activated carbon, as revealed by the increase of the number of C-H species at the borders of the graphenic domains. Overall, this work provides important insights for better understanding the complex nature of the interaction between H2 and Pt and Pd-loaded activated carbon catalysts.

In situ real-time neutron imaging of gaseous H2 adsorption and D2 exchange on carbon-supported Pd catalysts.

We use in situ neutron imaging to observe the adsorption/absorption of hydrogen within a packed catalyst bed of a Pd/C catalyst at a spatial and temporal resolution of ∼430 μm and a ∼9 s respectively. Additionally, the H2/D2 exchange process across the catalyst bed is followed in real time.

Robust O-Pd-Cl catalyst-electrolyte interfaces enhance CO tolerance of Pd/C catalyst for stable CO2 electroreduction

Carbon-supported Pd catalysts are highly active yet can be easily poisoned by the in-situ formed carbon monoxide (CO) during CO2 electrochemical reduction reaction (CO2RR). Herein, we introduce a novel approach to enhance the CO tolerance and activity of Pd/C catalyst by manipulating catalyst-electrolyte interfaces in saturated KCl electrolyte. During the CO2RR, the Cl- ions in electrolyte trigger the surface dynamic reconstruction of Pd/C catalyst with the formation of O-Pd-Cl species at catalyst-electrolyte interfaces. The reconstructed Pd/C catalysts can achieve nearly 100% of CO Faradaic efficiency and feature high stability and CO tolerance, which can maintain a better activity in the presence of over 2000 ppm and 23200 ppm of CO in H-type cell and flow cell, respectively. Meanwhile, using such highly concentrated electrolyte, the hydrogen evolution reaction is strongly suppressed. The experimental and theoretical results have confirmed that the O-Pd-Cl species mediated by Cl- ions enable the high activity, good CO resistance and long lifetime of the Pd/C catalyst. These findings may provide some inspirations into the design and fabrication of active yet stable Pd-based catalysts for CO2 electroreduction, and offer some insights into manipulation of the activity and stability for the Pd catalysts at catalyst-electrolyte interfaces.

Boosted H2O2 Productivity by Sulfur-Doped Pd/Carbon Catalysts via Direct Synthesis from H2 and O2 at Atmospheric Pressure

It remains a challenge nowadays in the development of highly efficient catalysts for the direct synthesis of H2O2 from H2 and O2. In this work, we developed sulfur-doped carbon-supported Pd catalysts and systematically investigated sulfur effects on catalytic performances through various characterizations (transmission electron microscopy (TEM), N2 adsorption–desorption, H2-temperature-programmed reduction (TPR)/temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), etc.). Results showed that sulfur species promoted the in situ formation of Pd nanoparticles and enhanced their dispersion on the supports. Due to the synergistic combination of active metal and support, the catalytic performance has been improved significantly in the direct synthesis of H2O2. The catalyst doped with the highest sulfur content showed the highest H2O2 productivity of 7148 mmol gPd–1 h–1, which was nearly 4 times higher than the catalyst without sulfur doping.

Porous carbon supported Pd catalysts derived from gelatin‐based/chitosan or polyvinyl pyrrolidone/PdCl2 blends

AbstractNovel N‐containing porous carbon supported Pd heterogeneous catalysts have been derived by carbonization of gelatin (GEL)/chitosan/PdCl2 (GEL/CS/PdCl2) and GEL/polyvinyl pyrrolidone/PdCl2 (GEL/PVP/PdCl2) blends under N2 atmosphere at 800°C. The microstructure of the resultant N‐containing carbon supported Pd heterogeneous catalysts can be tailored by the nature of the blended polymers. Much larger specific surface area, better dispersion of Pd0/PdO nanoparticles, higher Pd and N contents are found in the case of N‐containing porous carbon supported Pd heterogeneous catalysts derived from GEL/CS/PdCl2 blend system. When the mass ratio of GEL to CS is kept at 1/1, the surface area of 644.8 m2/g, rich porous structure, N % of 7.2%, and Pd0/PdO nanoparticles sized below 3 nm are obtained in the derived Pd@N‐C‐GEL/CS(1/1) catalyst. It shows excellent catalytic efficiency (higher than 90%) in Heck coupling reaction of aromatic halides and alkenes, and high recycling stabilities both in aqueous (9 runs) and organic (15 runs) phase. The high activity and stability of the novel Pd@N‐C‐GEL/CS(1/1) catalyst have been attributed to a combination of high porous structure, strong chelation of Pd species, high thermal stability, and good solvent‐resistant performances.

H2 Production from Formic Acid Using Highly Stable Carbon-Supported Pd-Based Catalysts Derived from Soft-Biomass Residues: Effect of Heat Treatment and Functionalization of the Carbon Support.

The production of hydrogen from liquid organic hydrogen carrier molecules stands up as a promising option over the conventional hydrogen storage methods. In this study, we explore the potential of formic acid as a convenient hydrogen carrier. For that, soft-biomass-derived carbon-supported Pd catalysts were synthesized by a H3PO4-assisted hydrothermal carbonization method. To assess the impact of the properties of the support in the catalytic performance towards the dehydrogenation of formic acid, three different strategies were employed: (i) incorporation of nitrogen functional groups; (ii) modification of the surface chemistry by performing a thermal treatment at high temperatures (i.e., 900 °C); and (iii) combination on both thermal treatment and nitrogen functionalization. It was observed that the modification of the carbon support with these strategies resulted in catalysts with enhanced performance and outstanding stability even after six consecutive reaction cycles, thus highlighting the important effect of tailoring the properties of the support.

Oxygen reduction reaction on Pd nanoparticles supported on novel mesoporous carbon materials

In this work three mesoporous nitrogen-doped carbon support materials were evaluated for oxygen reduction reaction (ORR) in comparison to Vulcan carbon in 0.1 M KOH and 0.5 M H2SO4 solutions. Palladium nanoparticles were synthesised using citrate method and the average particle size of 3.9 ± 0.6 nm was obtained, which was determined from transmission electron microscopy (TEM) images. Unique porosities of these mesoporous engineered catalyst supports (ECS) were evaluated using the BET method and all of the materials displayed similar microporosity, altrough mesopore distribution varied greatly between these materials. Three different loadings of the Pd catalyst were applied to the support materials (varying between 20-40 wt% of Pd) to evaluate the support ability to disperse a large amount of Pd. By comparing the 40 wt% Pd loaded ECS-003604 and Vulcan XC-72R it can be noted that the Vulcan carbon-supported Pd catalyst is more agglomerated. The agglomeration of this catalyst is also noticeable from cyclic voltammetry (CV) studies, where the PdO reduction peak shifts to more positive values as compared to the mesoporous Pd/C counterparts. The ORR kinetics were explored using the rotating disc electrode (RDE) method. In acidic media a Pd catalyst supported on a bimodal mesoporous ECS material showed highest specific activity for oxygen electroreduction, while in alkaline the activity difference is less noticeable between the Pd-based electrocatalyst materials. One of the mesoporous N-doped carbon supported Pd catalyst was also compared to Pd/Vulcan cathode in single-cell alkaline anion exchange membrane fuel cell and improved peak power density was observed.

Biomass Nanoporous Carbon-Supported Pd Catalysts for Partial Hydrogenation of Biodiesel: Effects of Surface Chemistry on Pd Particle Size and Catalytic Performance.

Two types of cattail flower-derived nanoporous carbon (NPC), i.e., NPC activated with KOH and H3PO4, were produced and characterized using several techniques (e.g., Raman spectroscopy, nitrogen adsorption, and X-ray photoelectron spectroscopy). The influence of the carbon support characteristics on the particle sizes and chemical states of Pd in the synthesized Pd/NPC catalysts, which affect the catalytic activity and product selectivity, was analyzed. The surface chemistry properties of NPC were the main factors influencing the Pd particle size; by contrast, the textural properties did not significantly affect the size of the Pd particles on NPC supports. The use of Pd nanoparticles supported on the rich-functionalized surface carbons obtained by H3PO4 activation led to superior catalytic activity for the polyunsaturated fatty acid methyl ester (poly-FAME) hydrogenation, which could achieve 90% poly-FAME conversion and 84% selectivity towards monounsaturated FAME after a 45-min reaction time. This is due to the small Pd nanoparticle size and the high acidity of the catalysts, which are beneficial for the partial hydrogenation of poly-FAME in biodiesel. Conversely, the Pd nanoparticles supported on the high-surface-area carbon by KOH activation, with large Pd particle size and low acidity, required a longer reaction time to reach similar conversion and product selectivity levels.

Generation of a Highly Efficient Electrode for Ethanol Oxidation by Simply Electrodepositing Palladium on the Oxygen Plasma-Treated Carbon Fiber Paper

In this study, a highly efficient carbon-supported Pd catalyst for the direct ethanol fuel cell was developed by electrodepositing nanostructured Pd on oxygen plasma-treated carbon fiber paper (Pd/pCFP). The oxygen plasma treatment has been shown to effectively remove the surface organic contaminants and add oxygen species onto the CFP to facilitate the deposition of nano-structured Pd on the surface of carbon fibers. Under the optimized and controllable electrodeposition method, nanostructured Pd of ~10 nm can be easily and evenly deposited onto the CFP. The prepared Pd/pCFP electrode exhibited an extraordinarily high electrocatalytic activity towards ethanol oxidation, with a current density of 222.8 mA mg−1 Pd. Interestingly, the electrode also exhibited a high tolerance to poisoning species and long-term stability, with a high ratio of the forward anodic peak current density to the backward anodic peak current density. These results suggest that the Pd/pCFP catalyst may be a promising anodic material for the development of highly efficient direct alcohol fuel cells.

Effect of Pd Precursor Salts on the Chemical State, Particle Size, and Performance of Activated Carbon-Supported Pd Catalysts for the Selective Hydrogenation of Palm Biodiesel.

To improve the oxidative stability of biodiesel fuel (BDF), the polyunsaturated fatty acid methyl esters (poly-FAME) presented in commercial palm oil-derived biodiesel fuel (palm-BDF) were selectively hydrogenated to monounsaturated fatty acid methyl esters (mono-FAME) under a mild condition (80 °C, 0.5 MPa) using activated carbon (AC)-supported Pd catalysts with a Pd loading of 1 wt.%. The partially hydrotreated palm-BDF (denoted as H-FAME) which has low poly-FAME components is a new type of BDF with enhanced quality for use in high blends. In this study, we reported that the chemical states and particle sizes of Pd in the prepared Pd/AC catalysts were significantly influenced by the Pd precursors, Pd(NO3)2 and Pd(NH3)4Cl2, and thus varied their hydrogenation activity and product selectivity. The 1%Pd/AC (nit) catalyst, prepared using Pd(NO3)2, presented high performance for selective hydrogenation of poly-FAME into mono-FAME with high oxidation stability, owning to its large Pd particles (8.4 nm). Conversely, the 1%Pd/AC (amc) catalyst, prepared using Pd(NH3)4Cl2, contained small Pd particles (2.7 nm) with a little Cl residues, which could be completely removed by washing with an aqueous solution of 0.1 M NH4OH. The small Pd particles gave increased selectivity toward unwanted-FAME components, particularly the saturated fatty acid methyl esters during the hydrogenation of poly-FAME. This selectivity is unprofitable for improving the biodiesel quality.

Hydrogenation of benzophenone by carbon-supported Pd catalysts

Catalytic activity of palladium catalysts with two different types of carbon support, Norit (an activated carbon), and bamboo-shaped carbon nanotubes (BCNT) have been tested for benzophenone hydrogenation. The selectivity toward the two possible reaction products (benzhydrol and diphenylmethane) can be directed by the catalyst support. It has been found that the Norit support preferred the over-hydrogenation of benzhydrol to diphenylmethane. The BCNT support proved to be much more selective and resulted as much as 99.3% benzhydrol selectivity at 96.3% benzophenone conversion. The high benzhydrol selectivity might be explained by the presence of covalently bonded nitrogen atoms in the catalyst (BCNT: 6.19 w/w%, Norit 0.54 w/w%) that can inhibit the over-hydrogenation process, thereby BCNTs are better catalyst supports for benzhydrol production than the commonly used activated carbon–supported catalysts.

Surface engineering of Rh-modified Pd nanocrystals by colloidal underpotential deposition for electrocatalytic methanol oxidation.

The development of methods to control the surface structures of metallic nanocatalysts is of vital importance for their application as heterogeneous catalysts in chemical conversions of energy and environmental and chemical engineering. The underpotential deposition (UPD) phenomenon has received considerable interest as a tool for the controllable synthesis of metal nanocrystals and engineering their catalytic performances. Herein, the discovery of UPD of Rh on Pd nanocrystals is reported. More importantly, the UPD of Rh is explored as a strategy to direct the synthesis of Rh-modified Pd nanocrystals with controllable shapes and surface structures. The mechanism of the UPD of Rh on Pd is elucidated in terms of electronegativity difference considerations. Compared with pristine Pd octahedral nanocrystals and commercial carbon-supported Pd catalysts, the Rh-modified Pd octahedral nanocrystals exhibit remarkable electrocatalytic performances during the methanol oxidation reaction in alkaline media. Our discovery heralds a new paradigm for UPD-mediated growth of metal nanocrystals and may provide a mechanistic understanding for the guided design of other colloidal UPD systems in the synthesis and surface engineering of metal nanocrystals.

Oxygen reduction reaction on Pd nanocatalysts prepared by plasma-assisted synthesis on different carbon nanomaterials

In this work He/H2 plasma jet treatment was used to reduce Pd ions in the aqueous solution with simultaneous deposition of created Pd nanoparticles to support materials. Graphene oxide (GO) and nitrogen-doped graphene oxide (NrGO) were both co-reduced with the Pd ions to formulate catalyst materials. Pd catalyst was also deposited on the surface of carbon black. The prepared catalyst materials were physically characterized using transmission electron microscopy, scanning electron microscopy and x-ray photoelectron spectroscopy. The plasma jet method yielded good dispersion of small Pd particles with average sizes of particles being: Pd/rGO 2.9 ± 0.6 nm, Pd/NrGO 2.3 ± 0.5 nm and Pd/Vulcan 2.8 ± 0.6 nm. The electrochemical oxygen reduction reaction (ORR) kinetics was explored using the rotating disk electrode method. Pd catalyst deposited on nitrogen-doped graphene material showed slightly improved ORR activity as compared to that on the nondoped substrate, however Vulcan carbon-supported Pd catalyst exhibited a higher specific activity for oxygen electroreduction.

Turnover Rate of Metal-Catalyzed Hydroconversion of 2,5-Dimethylfuran: Gas-Phase Versus Liquid-Phase

Hydroconversion (hydrogenation and hydrogenolysis) of biomass-derived furanic compounds giving furan ring-hydrogenation and ring-cleavage products attracts interest for sustainable production of chemicals and fuels. Here, the hydroconversion of 2,5-dimethylfuran (DMF), chosen as a model furanic compound, was investigated at a gas-solid interface over carbon-supported Pt, Pd, Rh and Ru metal catalysts in a fixed-bed reactor at 70–90 °C and ambient pressure. Pt/C was mainly active in ring cleavage of DMF to produce 2-hexanone as the primary product, followed by its hydrogenation to 2-hexanol and hexane. In contrast, Pd/C, Rh/C and Ru/C selectively hydrogenated the furan ring to 2,5-dimethyltetrahydrofuran (DMTHF). The turnover frequency (TOF) of metal sites in the gas-phase DMF hydroconversion was determined from zero-order kinetics in the absence of diffusion limitations. The TOF values decreased in the sequence Pt > Rh > Pd >> Ru, similar to the liquid-phase reaction. The TOF values for the gas-phase reaction were found to be one order of magnitude greater than those for the liquid-phase reaction. This indicates that the gas-phase process is potentially more efficient than the liquid-phase process. TOF values for hydroconversion of ring-saturated furan derivatives, tetrahydrofuran and DMTHF, on Pt/C, were much lower than those for DMF.

Geometric, electronic, and synergistic effect in the sulfonated carbon-supported Pd catalysts for the direct synthesis of hydrogen peroxide

Although carbon-supported palladium catalysts have been generally used for the direct synthesis of H2O2 (DSHP), the low H2O2 selectivity remains a challenge. In this work, it was systematically studied how the sulfonated carbon surface affects the physicochemical properties of Pd during catalyst preparation, and thereby affects the catalytic activity of Pd/C for the DSHP reaction. Nano-sized Pd particles (about 2–3 nm) with a high Pd2+/Pd0 ratio resulted in a high H2O2 selectivity. The sulfonated carbon material acted as an efficient solid acid support and enhanced the H2O2 selectivity. Fine-tuning the Pd properties on the sulfonated carbon support significantly improved the H2O2 selectivity by as much as 87 % in the absence of caustic promoters, which clearly demonstrates that the synergistic combination of the active metal properties and that of the carbon support are extremely important to realize a highly active and selective carbon-supported palladium catalyst for the DSHP reaction.