Sol Immobilization Research Articles

Pd‐Pt Bimetallic Catalysts for Enhanced Low‐Temperature Hydrodeoxygenation of Vanillin

AbstractTo make pyrolytic bio‐oil useful as a transportation fuel, the oxygen content must be reduced, and this can be carried out by using catalytic hydrodeoxygenation (HDO) reaction. The greatest challenge is associated with the removal of strongly bound oxygenated groups without saturating the aromatic ring while preserving the number of carbons. However, the development of a stable catalyst that can selectively remove such oxygenated groups with low hydrogen consumption is still challenging. In this context, a systematic study on HDO of vanillin on bimetallic Pd−Pt catalysts was carried out. It aims to study the effect of bimetallic synergy in terms of activity and selectivity to creosol. Metallic nanoparticles of Pd and Pt were synthesized by sol immobilization technique and deposited on TiO2. The conversion of vanillin was correlated to the Pd−Pt atomic ratio, while the production of the creosol was correlated to the Pd(0)/(Pd+Pt) ratio at the surface. Full conversion of vanillin was obtained at low reaction temperature (20 °C) achieving nearly 100 % selectivity to creosol. These results represent a step forward in advancing the development of more efficient and sustainable processes for bio‐oil upgrading.

Hydrogen Production from Hydrous Hydrazine Decomposition Using Ir Catalysts: Effect of the Preparation Method and the Support

Herein, Ir/CeO2 catalysts were prepared using the deposition–precipitation method with NaOH or urea as the precipitating agent or using sol immobilization with tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the protective and reducing agent. The effect of the preparation method on Ir catalyst activity was evaluated in the liquid-phase catalytic decomposition of hydrous hydrazine to hydrogen. Ir/CeO2 prepared using sol immobilization and DP NaOH showed the best activity (1740 h−1 and 1541 h−1, respectively) and yield of hydrogen (36.6 and 38.9%). Additionally, the effect of the support was considered, using TiO2 and NiO in addition to CeO2. For this purpose, the sol immobilization of preformed nanoparticles technique was considered because it allows the same morphology of the immobilized particles to be maintained, regardless of the support. Ir deposited on NiO resulted in the most selective catalyst with a H2 yield of 83.9%, showing good stability during recycling tests. The catalysts were characterized using different techniques: X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with an X-ray detector (EDX) and inductively coupled plasma–mass spectroscopy (ICP-MS).

Effects of alloying palladium with gold in furfural hydrogenation:An in situ ATR-IR spectroscopy and density functional theory study

Furfural is a versatile platform molecule and a model compound to explore the key factors influencing activity and selectivity in heterogeneous catalysis. In this study, Pd and AuPd nanoparticles (average size 3.5–4 nm) were deposited on TiO2 by sol immobilization method and were evaluated for liquid-phase furfural hydrogenation. Alloying Au and Pd caused a decrease in activity, an enhancement in stability, and a change in selectivity, favouring the complete hydrogenation of furfural over the decarbonylation reaction. These variations in catalytic performance were elucidated by combining in situ attenuated total reflectance infrared spectroscopy and density functional theory studies.

PHOTOCATALYTIC DEGRADATION OF 3-CHLOROPHENOL USING Pd/Ag DOPED ON P25 DEGUSSA TiO2 NANOPARTICLE WITH UV RADIATION

Photocatalytic degradation of 3-chlorophenol was investigated using Pd/Ag doped on P25 Degussa TiO2. The Pd/AgTiO2 photocatalysts were prepared by sol immobilization method. A fabricated photo-reactor was used in photocatalytic degradation of 3-chlorophenol and monitored using HPLC. The experimental results indicates that doping of Pd/Ag on TiO2 increases the photocatalytic efficiency of TiO2. The experimental results indicates that Pd/ TiO2 has a photodegradation efficiency of 40.44% while Ag/TiO2 has a photodegradation efficiency of 60.44%. The dried catalysts were subsequently used again under the same experimental condition with a fresh 3-chlorophenol up to four (4) times. The result indicates that the re-used catalysts remain active for up to four (4) times of usage with minor reduction in activity, which is attributed to metal leaching. Ag/TiO2 has higher rate constant of - 0.019 than Pd/TiO2 which is -0.031, the rate constant for the degradation followed first-order reaction kinetics. The photocatalytic degradation of 3-chlorophenol indicates unstable degradation due to effect of inductive and mesomeric effect which is less on meta-position. The use of nanotechnology in wastewater treatment plants to curtail the environmental and health consequences of a widespread of organic pollutants should be encouraged.

Iron-palladium supported graphene as an efficient bimetallic catalyst for the selective oxidation of benzyl alcohol to benzaldehyde

The catalytic oxidation of benzyl alcohol (OBA) is one of the significant methods to produce benzaldehyde, an essential reagent in the chemical and pharmaceutical industries. However, developing an active and efficient catalyst for OBA is a tremendous challenge in commercialization. This research describes a simple, eco-friendly method for producing Fe, Pd, and Fe: Pd bimetallic nanoparticles fabricated by sol immobilization over graphene to conduct OBA. The resulting composite nano-alloys were then characterized using X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The oxidation state and elemental composition of as-fabricated nanoparticles were analyzed using XPS. The point of zero charges (pHPZC) was analyzed and the PZC value indicated that the proposed adsorbent material tends to have a positive charge. The OBA reaction efficiency (87%) of bimetallic nanocatalysts stabilized in graphene support was increased through surface modification of the ratio of both metals. The experimental error was based on three parallel tests and the carbon balance (99.6%) was analyzed during the experiments A proposed reaction mechanism of OBA validated the β-hydride step's elimination by molecular oxygen converting the metal hydride into a water molecule, forming a peroxide intermediate to form water and oxygen molecules. The Fe on the nanocatalyst’s surface is preferentially responsible for the adsorption of the substrate molecule, resulting in the formation of metal-alkoxide. Since it lacks electrons, Fe is more likely to be oxidized, allowing it to perform better than monometallic catalysts in terms of catalytic activity. The present study has great potential to be applied on an industrial scale and studied for industrialists, researchers, and academicians.

A Facile Approach of Fabricating Bifunctional Catalysts for Redox Applications by Uniformly Immobilized Metallic Nanoparticles on NiCr LDH

This study discloses the development of NiCr LDH, Ag@NiCr LDH, and Pd@NiCr LDH bifunction catalysts using a hydrothermal coprecipitation method followed by sol immobilization of metallic nanoparticles. The structures and morphologies of the synthesized nanocomposites were analyzed using FTIR, XRD, XPS, BET, FESEM-EDX, and HRTEM. The catalytic effectiveness of the samples was evaluated by tracking the progression of NaBH4-mediated nitrobenzene (NB) reduction to aniline and CO oxidation using UV-visible spectrophotometry and an infrared gas analyzer, respectively. Pd@NiCr LDH displayed much higher performance for both reactions than the bare NiCr LDH. The catalyst Pd@NiCr LDH showed robust catalytic activity in both the oxidation of carbon monoxide (T50% (136.1 °C) and T100% (200.2 °C)) and NaBH4-mediated nitrobenzene reduction (98.7% conversion and 0.365 min-1 rate constant). The results disclose that the Ni2+@ Cr3+/Cr6+ @Pd° ion pairs inside the LDH act as a charge transfer center and hence significantly enhance the catalytic performance. As a result, this research offers the novel NiCr LDH catalyst as a bifunctional catalyst for air depollution control and the organic transformation process.

Bio-Adipic Acid Production from Muconic Acid Hydrogenation on Palladium-Transition Metal (Ni and Zn) Bimetallic Catalysts

The hydrogenation of muconic acid (MA) to bio-adipic acid (AdA) is one of the green chemical processes that has attracted the most interest in recent years. Indeed, MA can be readily obtained from biomass through fermentative processes. Here, we aimed to investigate the synergic effect of electronic promotion that the addition of a second metal, even in small quantities, can have on Pd-based catalyst, known for its low stability. Ni and Zn were taken into consideration and two different catalysts (1%Pd8Ni2/HHT and 1%Pd8Zn2/HHT) were synthetized by sol immobilization method and supported on high-temperature, heat-treated carbon nanofibers (HHT-CNFs) that are known to enhance the stability of palladium. The catalysts were tested in MA hydrogenation and thoroughly characterized by TEM, ICP, and XPS analysis to unveil the effect of the second metal. To solve the solubility issue and have a starting material as similar as feasible to the post-fermentation conditions of the biomass, sodium muconate salt was chosen as a substrate for the reaction. All of the synthetized bimetallic catalysts showed a higher activity than monometallic Pd and better stability during the recycling tests, pointing out that even a small amount of these two metals can increase the catalytic properties of monometallic Pd.

The Effect of Sibunit Carbon Surface Modification with Diazonium Tosylate Salts of Pd and Pd-Au Catalysts on Furfural Hydrogenation.

Herein, we investigated the effect of the support modification (Sibunit carbon) with diazonium salts of Pd and Pd-Au catalysts on furfural hydrogenation under 5 bars of H2 and 50 °C. To this end, the surface of Sibunit (Cp) was modified with butyl (Cp-Butyl), carboxyl (Cp-COOH) and amino groups (Cp-NH2) using corresponding diazonium salts. The catalysts were synthesized by the sol immobilization method. The catalysts as well as the corresponding supports were characterized by Fourier transform infrared spectroscopy, N2 adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The analysis of the results allowed us to determine the crucial influence of surface chemistry on the catalytic behavior of the studied catalysts, especially regarding selectivity. At the same time, the structural, textural, electronic and acid–base properties of the catalysts were practically unaffected. Thus, it can be assumed that the modification of Sibunit with various functional groups leads to changes in the hydrophobic/hydrophilic and/or electrostatic properties of the surface, which influenced the selectivity of the process.

Pd-Au nanoparticles supported reduced graphene oxide nanoplatelets toward aerobic selective oxidation of benzoyl alcohol

In this paper, mono-metallic catalysts, palladium (Pd) and gold (Au) and bi-metallic, Au-Pd supported on reduced graphene oxide (rGO) synthesized by Sol Immobilization technique. The as fabricated catalysts (Pd/rGO, Au/rGO and Au-Pd/rGO) have been tested by various techniques (Raman Spectroscopy, FE-SEM, XRD and TEM) to examine the structural, compositional and morphological characteristics. The performance of catalysts on the production of benzaldehyde via benzyl alcohol (BnOH) oxidation was investigated adopting H2O2 as an oxidizing agent. In general, Au-Pd/rGO catalyst presented a remarkable superiority over Au/rGO and Pd/rGO. The Au-Pd/rGO catalyst gave the best reaction conversion ratio of 24.3%, while its selectivity for benzaldehyde was 87.5% using 10 mg catalyst mass, reaction temperature 80 oC and 50% H2O2

Impact of the Experimental Parameters on Catalytic Activity When Preparing Polymer Protected Bimetallic Nanoparticle Catalysts on Activated Carbon.

Sol immobilization is used to produce bimetallic catalysts with higher activity to monometallic counterparts for a wide range of environmental and commercial catalytic transformations. Analysis of complementary surface characterization (XPS, Boehm’s titration, and zeta potential measurements) was used to elucidate alterations in the surface functionality of two activated carbon supports during acid exposure. When considered in parallel to the experimentally determined electrostatic and conformational changes of the polymer surrounding the nanoparticles, an electrostatic model is proposed describing polymer protected nanoparticle deposition with several polymer–carbon support examples described. Consideration of the electrostatic interactions ensures full deposition of the polymer protected nanoparticles and at the same time influences the structure of the bimetallic nanoparticle immobilized on the support. The normalized activity of AuPd catalysts prepared with 133 ppm H2SO4 has a much higher activity for the direct synthesis of hydrogen peroxide compared to catalysts prepared in the absence of acid. Detailed characterization by XPS indicates that the surface becomes enriched in Au in the Au–Pd samples prepared with acid, suggesting an improved dispersion of smaller bimetallic nanoparticles, rich in Au, that are known to be highly active for the direct synthesis reaction. Subsequent microscopy measurements confirmed this hypothesis, with the acid addition catalysts having a mean particle size ∼2 nm smaller than the zero acid counterparts. The addition of acid did not result in a morphology change, and random alloyed bimetallic AuPd nanoparticles were observed in catalysts prepared by sol immobilization in the presence and absence of acid. This work shows that the deposition of polymer protected AuPd nanoparticles onto activated carbon is heavily influenced by the acid addition step in the sol immobilization process. The physicochemical properties of both the polymer and the activated carbon support should be considered when designing a bimetallic nanoparticle catalyst by sol immobilization to ensure the optimum performance of the final catalyst.

Temperature-Dependent Activity of Gold Nanocatalysts Supported on Activated Carbon in Redox Catalytic Reactions: 5-Hydroxymethylfurfural Oxidation and 4-Nitrophenol Reduction Comparison

In this study, the temperature-dependent activity of Au/AC nanocatalysts in redox catalytic reactions was investigated. To this end, a series of colloidal gold catalysts supported on activated carbon and titania were prepared by the sol immobilization method employing polyvinyl alcohol as a polymeric stabilizer at different hydrolysis degrees. The as-synthesized materials were widely characterized by spectroscopic analysis (XPS, XRD, and ATR-IR) as well as TEM microscopy and DLS/ELS measurements. Furthermore, 5-hydroxymethylfurfural (HMF) oxidation and 4-nitrophenol (4-NP) reduction were chosen to investigate the catalytic activity as a model reaction for biomass valorization and wastewater remediation. In particular, by fitting the hydrolysis degree with the kinetic data, volcano plots were obtained for both reactions, in which the maximum of the curves was represented relative to hydrolysis intermediate values. However, a comparison of the catalytic performance of the sample Au/AC_PVA-99 (hydrolysis degree of the polymer is 99%) in the two reactions showed a different catalytic behavior, probably due to the detachment of polymer derived from the different reaction temperature chosen between the two reactions. For this reason, several tests were carried out to investigate deeper the observed catalytic trend, focusing on studying the effect of the reaction temperature as well as the effect of support (metal–support interaction) by immobilizing Au colloidal nanoparticles on commercial titania. The kinetic data, combined with the characterization carried out on the catalysts, confirmed that changing the reaction conditions, the PVA behavior on the surface of the catalysts, and, therefore, the reaction outcome, is modified.

Acceptorless dehydrogenation of 1-phenylethanol using Pd/TiO2 catalysts prepared by sol immobilisation

Reversible hydrogenation and acceptorless dehydrogenation of organic molecules would enable pre-existing technologies and infrastructure to be leveraged for the storage and transport of hydrogen. We report the synthesis of active Pd/TiO2 catalysts prepared by sol immobilisation for the acceptorless dehydrogenation of 1-phenylethanol to acetophenone with evolution of molecular hydrogen. The catalyst converts 1-phenylethanol with a TOF of 3600 mol1-PE h−1 molPd−1 while maintaining high selectivity (>95%) at over 80% conversion. This represents a 3.5 x increase in catalytic activity with comparable selectivity over commercially available 5% Pd/C catalysts.

Pd–Au Bimetallic Catalysts for the Hydrogenation of Muconic Acid to Bio-Adipic Acid

The hydrogenation reaction of muconic acid, produced from biomass using fermentative processes, to bio-adipic acid is one of the most appealing green emerging chemical process. This reaction can be promoted by catalysts based on a metal belonging to the platinum group, and the use of a second metal can preserve and increase their activity. Pd–Au bimetallic nanoparticle samples supported on high-temperature, heat-treated carbon nanofibers were prepared using the sol immobilization method, changing the Pd–Au molar ratio. These catalysts were characterized by TEM, STEM, and XPS analysis and tested in a batch reactor pressurized with hydrogen, where muconic acid dissolved in water was converted to adipic acid. The synthesized Pd–Au bimetallic catalysts showed higher activity than monometallic Au and Pd material and better stability during the recycling tests. Moreover, the selectivity toward the mono-unsaturated changed by decreasing the Pd/Au molar ratio: the higher the amount of gold, the higher the selectivity toward the intermediates.

Disclosing the Role of Gold on Palladium – Gold Alloyed Supported Catalysts in Formic Acid Decomposition

AbstractHerein, we report the synthesis of preformed bimetallic Pd‐Au nanoparticles supported on carbon nanofibers with different Pd : Au atomic ratio (nominal molar ratio: 8–2, 6–4, 4–6, 2–8) and the corresponding Pd and Au monometallic catalysts by sol immobilization method. The obtained materials were characterized thoroughly by Transmission Electron Microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP‐OES). The catalytic performances of the Pd‐Au catalysts were evaluated in the aqueous phase dehydrogenation of formic acid (FA) at room temperature obtaining enhanced activity, stability and selectivity compared to the monometallic systems. In particular, Pd6Au4 and Pd8Au2 showed the best combination of catalytic properties, i. e., high selectivity to H2 and improved catalytic stability. Density functional theory (DFT) calculations on Pd15, Au15 and Pd9Au6 clusters supported on a carbon sheet were then simulated to provide atomic level understanding to the beneficial effect of gold observed in the experimental results. Au15 barely adsorb FA, while Pd15 possesses an adsorption energy higher than Pd9Au6. Dehydrogenation and dehydration pathways were followed on all these models. For Pd9Au6, the most favourable route was the formation of carbon dioxide and hydrogen. Analysis of the electronic structures was also performed on the different models showing a stronger interaction between the bimetallic system and the support proving the alloy superior stability.

Activated Carbon-Supported Ruthenium as a Catalyst for the Solvent- and Initiator-Free Aerobic Epoxidation of Limonene

The activity and selectivity of ruthenium catalysts supported on various activated carbons have been investigated in the epoxidation of limonene using molecular oxygen, the greenest oxidizing agent, under solvent/reductant- and initiator-free reaction conditions. The catalysts were prepared via different methods including impregnation, sol immobilization, and cation exchange. Supported Ru catalysts with a metal particle size ranging from 1.8 to 21 nm were obtained. The catalyst prepared by cation exchange using Darco G60, with the highest mesopore surface area and pore volume and the lowest Ru particle size (1.8 nm), was found to give the best combination of limonene conversion of 35% and higher selectivity for epoxidation products (Sepox) of 57% at 80 °C and 3 bar oxygen pressure, compared to the total selectivity of 25.5% for allylic oxidation products (Sallyl). Other activated carbon supports, e.g., Darco MRX, Norit RB4C, and Norit RX3, were found to yield less effective catalysts. In addition, the sol immobilization method led to the highest conversion of limonene (40.4%) but with a lower total selectivity toward epoxidation products (Sepox) of 36.8% and that toward allylic oxidation products (Sallyl) of 33.6%. The textural parameters of carbon-supported Ru catalysts were determined by BET, TEM, SEM, TPR, and CO chemisorption. Highly dispersed Ru particles were found to promote the formation of limonene epoxides via the reaction of limonene hydroperoxide with limonene instead of hydroperoxide decomposition to allylic radicals. Finally, the appropriate reaction conditions to maximize the selectivity of the epoxides and the reusability of the catalyst were established.

Enhancing activity, selectivity and stability of palladium catalysts in formic acid decomposition: Effect of support functionalization

In this work, palladium nanoparticles were deposited on oxygen and phosphorous functionalised carbon nanofibers (CNFs) by sol immobilisation method in order to investigate the support-metal effect on the formic acid (FA) decomposition reaction. In order to establish the presence of functional groups in the support and their effect on Pd nanoparticles, the obtained samples were then, characterised by Transmission Electron Microscopy (HR-TEM, STEM-HAADF and STEM-EDS) and X-ray photoelectron spectroscopy (XPS). FA catalytic decomposition performance, the stability and selectivity of the catalysts were evaluated in liquid-phase at mild reaction conditions. The effect of the metal-support interaction in the reactivity and stability of the catalysts was demonstrated leading to superior catalytic properties in both the functionalised materials. Density functional theory (DFT) simulations provided further insights in the interaction of Pd15 cluster with different support surfaces, i.e. pristine graphene (PG), carboxyl doped graphene (G_COOH), hydroxyl doped graphene (G_OH), carbonyl doped graphene (G_CO) and phosphate doped graphene (G_PO3H). The cluster-support interaction strength follows the trend Pd/G_CO > Pd/G_COOH > Pd/G_OH > Pd/G_PO3H > Pd/PG, confirming the increased stability of 1 wt% Pd@O-HHT and 1 wt% Pd@P-HHT observed in the experimental results.

Highly Selective Au/ZnO via Colloidal Deposition for CO2 Hydrogenation to Methanol: Evidence of AuZn Role

Gold, Au nanoparticles were deposited on ZnO, Al2O3, and Ga2O3 via colloidal method in order to investigate the role of support for CO2 hydrogenation to methanol. Au/ZnO was also produced using impregnation method to investigate the effect of colloidal method to improve methanol selectivity. Au/ZnO produced via sol immobilization showed high selectivity towards methanol meanwhile impregnation method produced Au/ZnO catalyst with high selectivity towards CO. The CO2 conversion was also influenced by the amount of Au weight loading. Au nanoparticles with average diameter of 3.5 nm exhibited 4% of CO2 conversion with 72% of methanol selectivity at 250 °C and 20 bar. The formation of AuZn alloy was identified as active sites for selective CO2 hydrogenation to methanol. Segregation of Zn from ZnO to form AuZn alloy increased the number of surface oxygen vacancy for CO2 adsorption to form formate intermediates. The formate was stabilized on AuZn alloy for further hydrogenation to form methanol. The use of Al2O3 and Ga2O3 inhibited the formation of Au alloy, and therefore reduced methanol production. Au/Al2O3 showed 77% selectivity to methane, meanwhile Au/Ga2O3 produced 100% selectivity towards CO. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synthesis of Bimetallic Au–Pt / TiO2 Catalysts as an Efficient Catalyst for the Photodegradation of Crystal Violet Dye

Bimetallic Au –Pt catalysts supporting TiO2 were synthesised using two methods; sol immobilization and impregnation methods. The prepared catalyst underwent a thermal treatment process at 400◦ C, while the reduction reaction under the same condition was done and the obtained catalysts were identified with transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). It has been found that the prepared catalysts have a dimension around 2.5 nm and the particles have uniform orders leading to high dispersion of platinum molecules .The prepared catalysts have been examined as efficient photocatalysts to degrade the Crystal violet dye under UV-light. The optimum values of Bimetallic Au –Pt catalysts supporting TiO2 have been found (0.05g of the catalyst prepared in sol immobilization method, 0.07 g of the synthesised in impregnation procedure. The impact of pH on the degradation reaction was tested; it has been found that pH 10 is the best media for the reaction. The effect of temperature has been discussed when various temperatures were used, and the heat of photoreaction Ea was estimated from the Arrhenius relationship, it has been concluded that the reaction is independent of temperature as the activation energy was very small (Ea= 22 kJ/ mole). The thermodynamic functions; entropy, enthalpy and the free energy have been figured out. It has been found that the positive values of enthalpy ∆H# refer to endothermic reaction, moreover, it has been demonstrated that the photoreaction is an endergonic one according to the calculated values of the free energy of activation. It has been noticed that when temperature increases, it promotes the production of free radicals, but it has been noticed that exceeding the temperature more than the used range causes reducing the percentage of degradation of crystal violet, the reason is due to the limitation conditions of adsorption process at higher temperature on the surface of the catalyst.

Au-Pd Bimetallic Nanocatalysts Incorporated into Carbon Nanotubes (CNTs) for Selective Oxidation of Alkenes and Alcohol

Although supported bimetallic nanoparticles (Au-Pd NPs) demonstrate outstanding efficiency, challenges appear for carbon supported small and stable bimetallic nanoparticles used in liquid-phase reactions. In this work, Au-Pd NPs were supported on two types of carbon nanotubes: CNTs decorated covalently with carboxylic acid groups (O-CNTs) and non-covalently with the conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer (P-CNTs). The Au-Pd NPs were prepared using the sol immobilization approach on the functionalized CNTs, and the effect of the utilized functionalization method on the properties of the immobilized metallic nanoparticles and the performance of the nanocomposite catalysts was investigated. The fabricated nanocomposites were characterized using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The catalytic performance of Au-Pd/O-CNTs and Au-Pd/P-CNTs was exploited for the oxidation of both cyclooctene and benzyl alcohol. Oxidation and polymer decoration directly led to an enhancement in the performance of CNTs catalysts. The nanocomposite catalyst with oxidized CNTs (Au-Pd/O-CNTs) was also found to be much more efficient and robust than that with polymer decorated CNTs (Au-Pd/P-CNTs). The enhancement in the oxidation of both cyclooctene and benzyl alcohol on Au-Pd/O-CNTs is attributed to the well-dispersed and smaller Au-Pd NPs as active sites on the surface of O-CNTs as compared to the P-CNTs surface.

Ligand effect of gold colloid in the preparation of Au/Nb2O5 for CO oxidation

Sol immobilization method by using a ligand-protected gold colloid precursor, Aun(SC12H25)m, was applied for the deposition of gold on Nb2O5 which is a typical solid acid. The effects of the thiolate ligand on the preparation of Au/Nb2O5 and on the catalytic activity for CO oxidation were investigated. Although most of the thiolate ligands were removed during the calcination at 300 °C, a small amount of sulfur species still remained on the catalyst, which played an important role for preventing the aggregation of the gold nanoparticles to give ca. 2.8 nm in a mean diameter with the gold loading amounts in the range from 0.9 wt% to 4.2 wt%. Calcination at a lower temperature (250 °C) gave a larger amount of the sulfur species than did the calcination at 300 °C, lowering catalytic activity for CO oxidation. The temperature for 50% CO conversion (T50%) was 3 °C for 0.9 wt% Au/Nb2O5 under 20,000 mL h−1 gcat−1 using 1 vol% CO in air. With an increase in the loading amount of gold, the catalytic activity became higher. The T50% of 4.2 wt% Au/Nb2O5 was −41 °C and turnover frequency (TOF) based on a number of the perimeter gold atom was calculated to be 8.7 s−1 at 20 °C. The TOF value obtained by Au/Nb2O5 prepared by deposition-reduction without thiolate ligands was 5.0 s−1. This result suggests that the sulfur remained on the catalyst did not inhibit CO oxidation.