Supported Metal Catalysts Research Articles

Operando induced strong metal-support interaction of Rh/CeO2 catalyst in dry reforming of methane

Strong metal-support interaction (SMSI) is an important concept in heterogeneous catalysis that has a profound effect on the structure and activity of the supported metal catalyst. However, the catalyst with an uncontrolled SMSI state significantly prevents the accessibility of metal surface to reactants by encapsulation process which inevitably limits their practical application. Herein, we demonstrate that under the reaction condition of dry reforming of methane (DRM), the occurrence of SMSI (CO2-SMSI) can be operando induced between Rh and CeO2 which significantly improves the catalytic activity in DRM reaction. Detailed study has revealed that the formation of suitable Rhδ+/Rh0 species in CO2-SMSI is critical in improving CH4 activation, while the presence of permeable encapsulation layer is helpful to provide more active sites. This discovery provides a new approach to overcome the limitation of classical SMSI catalyst in DRM reaction.

Ultrafine Ru nanoparticles on nitrogen-doped CNT arrays for HER: A CVD-based protocol achieving microstructure design and strong catalyst-support interaction

Strong metal-support interactions (SMSIs) play a pivotal role in enhancing the catalytic activity and stability of supported metal catalysts in heterogeneous thermal catalysis, but construction of effective SMSIs remains challenging in electrocatalysis. As a ubiquitous and versatile support for electrocatalysts, carbon materials are generally too inert to generate SMSIs with the loaded metal active sites. We hereby report a CVD-based method to prepare Ru nanoparticles on arrays of oxygen- and nitrogen-doped CNTs grown on the fibers of carbon paper (Ru/ONCNT@CP). The SMSIs were manifested by electronic structure tuning of Ru nanoparticles and their partial embedment in the carbon support. The SMSIs result in optimized Gibbs free energy of H*, lowered energy barrier of H2O dissociation, and enhanced catalyst robustness. Combined with the hierarchical microstructure, high surface area and hydrophilic/aerophobic nature, the Ru/ONCNT@CP electrode displays excellent HER catalytic activity in 1 M KOH, requiring overpotentials of only 73, 180, and 252 mV to achieve current densities of 100, 500, and 800 mA cm−2, respectively. Moreover, the Ru/ONCNT@CP electrode exhibits outstanding stability, with negligible current decay after 120 h HER operation at 100 mA cm−2. This work features an effective and scalable approach for preparation of metal-loaded-carbon electrocatalysts with engineered microstructure and SMSIs.

Oxygen vacancy-driven strong metal-support interactions on AuPd/TiO2 catalysts for high-efficient air-oxidation of 5-hydroxymethylfurfural

The regulation ofstrong metal-support interactions (SMSI) has emerged as a powerful strategy in boosting catalytic activity and controlling product selectivity. However, directly tuning the metal-supportinteractions in oxide supported metal nanocatalysts remains challenging. Herein, citric acid (CA)‑assisted synthesized TiO2 layer on halloysite nanotubes (HNTs) with varied oxygen vacancies (Ov) concentrations was designed for loading AuPd nanoparticles. SMSI between the AuPd nanoparticles and the TiO2-xCA@HNTs support was successfully induced by adjustable Ov concentrations. The synthesized catalyst was employed for air-oxidation of bio-based 5-hydroxymethylfurfural (HMF) to bioplastic monomer 2,5-furandicarboxylic acid (FDCA) in water. A satisfactory FDCA yield of 98.4 %, accompany with an outstanding FDCA formation rate of 900.9 mmol·g−1·h−1 and an excellent TOF value at 441.2 h−1 was afforded. Based on catalysts characterizations and experimental studies, the catalytic performance was significantly affected by Ov concentrations. The kinetic study showed that the supported gold nanoparticles in alkaline environment had strong aldehyde oxidation activity but weak alcohol oxidation ability. On the contrary, supported palladium nanoparticles were more conducive to alcohol oxidation. This imbalance was overcome by the loading of AuPd nanoparticles, which enhanced the activity for air-oxidation of HMF. Mechanistic studies demonstrated that the stronginteractions between noble metal nanocatalysts and supports were regulated by Ov, which not only increased the adsorption capacity of the substrate and crucial intermediate, but also facilitated the adsorption and activation of molecular oxygen to generate oxygen active species of superoxide radicals. The possible catalytic mechanism for air-oxidation of HMF over Ov-driven SMSI on the obtained catalysts was proposed. This work sheds lights on the design of supported metal catalysts with SMSI for the catalytic upgrading of biomass-derived platform chemicals.

Pt Nanoparticles on Beta zeolites for Catalytic Toluene Oxidation: Effect of the Hydroxyl Groups of Beta Zeolite**

AbstractStabilisation of metal species using hydroxyl‐rich dealuminated zeolites is a promising method for catalysis. However, insights into the interactions between the hydroxyl groups in zeolite and noble metals and their effects on catalysis are not yet fully understood. Herein, comparative studies were conducted using Pt catalysts supported on hydroxyl‐rich dealuminated Beta (deAl‐Beta) and the pristine proton‐form Beta (H‐Beta) for catalytic oxidation of toluene. The findings suggest that during impregnation the Pt precursor (i. e., Pt(NH3)4(NO3)2) interacted with different sites on deAl‐Beta and H‐Beta, leading to the formation of supported Pt nanoparticles with different physicochemical properties. In detail, for H‐Beta, the Pt precursor interacted with Al‐OH and isolated external Si‐OH sites, yielding Pt NPs with a higher Pt0 proportion of ~71 % compared to ~57 % Pt0 on deAl‐Beta. Comparatively, abundant hydroxyl groups on deAl‐Beta such as silanol nest and isolated internal Si‐OH stabilised highly active Pt‐O species. The resulting Pt/deAl‐Beta exhibited improved activity and anti‐coking ability than Pt/H‐Beta in catalytic toluene oxidation. For example, the temperature for 50 % toluene conversion was 193 °C for Pt/deAl‐Beta vs. 232 °C for Pt/H‐Beta, and the coke deposition was 1.7 % vs. 6.7 % (after the 24‐h longevity test), respectively. According to the toluene‐temperature programmed desorption (toluene‐TPD), 1H nuclear magnetic resonance (1H NMR) relaxation and in situ diffuse reflection Fourier transform spectroscopy (in situ DRIFTS) characterisation, the enhanced performance of Pt/deAl‐Beta could be ascribed to (i) the active Pt‐O sites stabilised by hydroxyl groups, which interact with toluene easily for conversion, and (ii) the acid‐free feature of the deAl‐Beta support, which avoids the formation of coke precursors (such as benzoate species) on the catalyst surface. Findings of the work can serve as the design guidelines for making effective supported metal catalysts using zeolitic carriers.

Pyrochlore@PBA derived electrocatalyst containing Ru nanoparticle and NiFe alloy for the oxygen evolution and reduction reactions

Developing enhanced electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for commercializing green energy technologies, such as Zn–air batteries. In this study, a uniquely designed metal catalyst–support material composite was synthesized using a Prussian blue analogue (PBA) and Y2Ru2O7 (YRO) pyrochlore for Zn-air battery. P–S-doped Ru nanoparticles and PBA-derived NiFe alloys anchored on the YRO pyrochlore (YRO@NiFe/Ru-PS) were synthesized in one pyrolysis process via in situ exsolution. The electronic structure of the Ru and NiFe particles was tailored by the pyrochlore support and P–S dual doping, which decreased the energy barrier for the catalytic reaction. YRO@NiFe/Ru-PS exhibited outstanding OER (overpotential = 241 mA/cm2; Tafel slope = 36 mV/dec) and ORR (half-wave potential = 0.83 V; Tafel slope = 65 mV/dec) performances. Furthermore, it also exhibited high performance in Zn–air battery applications (power density = 112 mW/cm2). This paper proposes an efficient and unique design strategy for developing OER/ORR bifunctional electrocatalysts.

Monitoring Structural and Electronic Changes of Supported Metal Catalysts Using Combined X‐Ray Techniques

Supported metal nanoparticle catalysts have become increasingly crucial for many catalytic applications. However, long‐term catalyst stability remains a problem due to catalyst deactivation caused by coke formation and sintering. The deposition of a thin overcoating via atomic layer deposition (ALD) onto metal‐supported nanoparticles has shown to greatly inhibit catalyst deactivation. This work utilizes a model catalyst system comprised of Pt nanoparticles supported on Al2O3 to demonstrate the effect of an atomically thin overcoating on supported metal nanoparticles. Continuous operando small‐angle X‐ray scattering (SAXS) and X‐ray absorption near edge spectroscopy (XANES) monitor structural and electronic changes to the catalyst and overcoating during calcination. SAXS data fitting reveals the formation of nanopores in the overcoating at high temperatures, while XANES monitors the oxidation state of the Pt catalyst. Herein, the usefulness of combined X‐ray techniques is demonstrated to characterize supported metal catalysts to further understanding of the synergistic effects of the ALD overcoating to aid in the design of new catalyst materials.

Selective formation of fuel BXT compounds from catalytic hydrodeoxygenation of waste biomass over Ni-decorated beta-zeolite

Upgrading of bio-oil extracted from the various components of biomass into transportation fuels is typically attained via surface-assisted hydrodeoxygenation (HDO) reactions. Date palm (Phoenix dactylifera) pits constitute an important category of waste biomass in many parts of the world. Herein, we report a comprehensive integrated experimental-simulation approach to investigate HDO process of vapor fraction generated from pyrolysis of date pits over the metal-supported catalyst Ni/H-Beta zeolite. The catalyst was synthesized and characterized using various techniques including XRD, FTIR, SEM-EDX, and TPR. Catalytic tests were carried out in a 2-stage catalytic reactor where pyrolysates from the first reactor flows over the catalyst placed in the second reactor. Selective formation of toluene (and other alkylated benzenes) indicates a profound selectivity towards the formation of benzene-toluene-xylene (BXT) fractions especially in the temperature range 200–400 °C. As the temperature increases, fragmentation and bimolecular reactions involving toluene leads to synthesis of unwanted PAHs, most notably azulene. Considering 3,4-altrosan as a model compound for the lignin content in date pits, governing mechanisms of HDOs, was mapped out using density functional theory (DFT) calculations. Results reported herein are expected to assist in the optimizing operational conditions that leads to the production of the valuable BXT fraction from pyrolysis of date pits.

Nitrogen-doped porous alumina for supported metal catalysts: Sintering resistance effect

A protocol has been proposed for modifying a porous alumina support by NO treatment to increase the resistance of metal particles on the support to sintering. The stabilization effect by forming AlNxOy species has been clearly demonstrated for supported platinum catalysts.

Catalytic hydrothermal liquefaction of alkali lignin for monophenols production over homologous biochar-supported copper catalysts in water

Constructing an advanced catalytic system for the purposeful liquefaction of lignin into chemicals has presented a significant prospect for sustainable development. In this work, the catalytic process of mesoporous homologous biochar (HBC) derived from alkali lignin supported copper catalysts (Cu/HBC) was reported for catalytic liquefaction of alkali lignin to monophenols. The characterization results revealed HBC promoted the formation of metal-support strong interaction and the generation of oxygen vacancies, enhancing the acid sites of Cu/HBC. Under the optimal conditions (0.2 g alkali lignin, 280 °C, 0.05 g Cu/HBC, 6 h, 18 mL water), the monophenol yield reached 75.01 ± 0.76 mg/g, and the bio-oil yield was 57.98 ± 1.76%. The copious mesopores, high surface area, and rich acidic sites were responsible for the high activity of Cu/HBC, which significantly outperformed the controlled catalysts, such as HBC, commercial activated carbon (AC), and reported Ni/AC, Ni/MCM-41, etc. In four consecutive runs, the catalytic performance of Cu/HBC was only reduced by 3.65% per cycle. Interestingly, catechol was selectively produced with Cu/HBC, which provided an effective strategy for the conversion of G/S-type lignin to catechyl phenolics (C-type). These findings indicate that the Cu/HBC will be a promising substitution of noble metal-supported catalysts for conversion biomass into high value-added phenolics.

Strong Metal-Support Interactions Stabilize Pt Nanocatalysts for Ceramic Fuel Cells

Nano-sized metal particles are widely used in various chemical/electrochemical fields due to their excellent catalytic activity, but they still suffer from deactivation by sintering, and this leads to serious issues regarding the price and lifespan of catalysts. In this study, we demonstrate that the introduction of nanoscale amorphous TiOx via atomic layer deposition can significantly improve the dispersion and durability of supported Pt nanocatalysts. An ultrathin TiOx layer (< 1 nm) deposited on a conductive Pr0.5Ba0.5MnO3 electrode, with a deposition time of less than 1 min, provides nucleation sites for the Pt nanocrystals impregnated thereon and promotes the migration of TiOx to the Pt surface, creating a metal-oxide interface. As a result, when applied to ceramic fuel cells, the TiOx undercoat achieves remarkable power density increases of over 100% and 400%, respectively, for wet (3% H2O) H2 and CH4 fuels without degradation at 700 °C for 120 h. These observations provide an innovative direction for the design of supported metal catalysts for high-temperature applications.

Stereoselective hydrogenation of guaiacol to cis-2-methoxycyclohexanol using supported rhodium catalysts in supercritical carbon dioxide

Selective hydrogenation of lignin-derived phenolic monomer to valuable chemicals has attracted attention and investigated well; however, stereoselective hydrogenation is required for practical applications, and is still challenging. In this study, we examined the stereoselective hydrogenation of guaiacol to cis-2-methoxycyclohexanol over supported metal catalysts in several solvents at mild reaction conditions. Rh/C in supercritical CO2 gave a higher proportion of cis-2-methoxycyclohexanol in total 2-methoxycyclohexanol compared to water solvent. Finally, guaiacol could be stereoselectively hydrogenated to cis-2-methoxycyclohexanol with the yield 83.9 % (total 2-methoxycyclohexanol yield was 95.5 %) even at 313 K for 1 h using the Rh/C catalyst in supercritical CO2 (CO2 25 MPa, H2 1.5 MPa).

From Basic Research on Supported-Metal Catalysts to their Practical Applications for Reduction of Food Waste

Abstract Supported metal catalysts are one of the most important heterogeneous catalysts, and they are widely used in chemical processes such as naphtha reforming, purification of exhaust gas from automobiles and so on. However, rational design of supported metal catalysts is still a target in heterogeneous catalysis. The author had a hypothesis that metal nanoparticles in ordered pores of zeolite or mesoporous silica may exhibit novel catalytic properties. Based on this idea, we used micropores of zeolites to accommodate metal carbonyl clusters, and then mesoporous silica to prepare metal nanoparticles. First, we studied ship-in-bottle synthesis of Rh carbonyl clusters in zeolite and its reactivity. Rh6(CO)16 was synthesized in NaY zeolite accompanied with formation of a mononuclear Rh(CO)2, which acted as a carrier of 13CO in 12CO-13CO exchange reaction. Then we worked on synthesis of platinum nanoparticles in mesoporous silica, and found that high activity in preferential oxidation of CO in hydrogen and in low-temperature oxidation of ethylene. The high catalytic performance in ethylene oxidation has led to practical application of platinum/silica catalysts for preservation of fruits and vegetables, resulting in reduction of food waste. This article describes the development process of this research.

CatMass: software for calculating optimal sample masses for X-ray absorption spectroscopy experiments involving complex sample compositions.

This paper presents software for calculating the optimal mass of samples with complex compositions (e.g. supported metal catalysts) for X-ray absorption spectroscopy (XAS) and scattering measurements. The ability to calculate the sample mass and other relevant parameters needed for an XAS measurement allows experimentalists to be better prepared in terms of detector selection, energy range of scan and overall time needed to complete the measurement, thus increasing efficiency. CatMass builds on existing sample mass calculators allowing users to determine the optimum sample preparation, collection geometry, usable energy range for a scan and approximate edge step of the absorption event. Visualization tools present the absorption calculation results in a format familiar to XAS experimentalists, with the added ability to save calculations and plots for future reference or recalculation. CatMass is a program broadly applicable in catalysis and is helpful for users with complex samples due to composition/stoichiometry or multiple competing elements.

Excellent low-temperature activity for oxidation of benzene serials VOCs over hollow Pt/CoMn2O4 sub-nanosphere: Synergistic effect between Pt and CoMn2O4 on improving oxygen activation

Constructing the interfacial active sites between noble metals and oxides is an effective way to enhancing the catalytic performance of noble metal-supported catalysts. Meanwhile, ultra-low dosage of the noble metal Pt but obtaining favorable catalytic activity is still major challenge to prepare noble metal-supported catalysts. Herein, the active Pt-CoMn2O4 interface with strong metal-support interaction (SMSI) is designed by loading ultra-low Pt content (0.12 wt%) on hollow structured CoMn2O4 sub-nanosphere (Pt/CoMn2O4). Compared with the reference MnOx, CoMn2O4 and Pt/MnOx, Pt/CoMn2O4 shows excellent catalytic activity even in presence of H2O, which is capable of completely converting toluene, ethylbenzene and o-xylene at 163, 207 and 218 °C, respectively. Various characterizations and density functional theory (DFT) calculations are performed to reveal the role of CoMn2O4 and specify the synergistic effect between Pt and CoMn2O4 on surface properties and catalytic performance. Intriguingly, in situ-designed temperature-programmed techniques and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy clarify the substitution of Co in CoMn2O4 enhances oxygen mobility, and the interface of Pt and support is the active sites for gaseous oxygen activation can also be confirmed by DFT calculation results. This SMSI is prone to promote the supplement of active oxygen species that is essential for excellent low-temperature catalytic oxidation performance. This study provides a new insight into the design of high-performance noble metal catalysts, and the understanding of textural structure, active species, synergistic effect, and mechanisms of catalytic systems.

Enhanced catalytic stability and structural evolution of Rh-BN interface in dry reforming of methane under intensified CO2 partial pressure

Strong metal-support interaction (SMSI) is a crucial factor that determines the structure and performance of a supported metal catalyst. Herein, the SMSI effect of Rh nanoparticle catalyst supported on h-BN is investigated in the dry reforming of methane (DRM) reactions with different CO2/CH4 ratios. The catalyst characterization results demonstrate that the SMSI effect allows the Rh nanoparticles to be encapsulated by BOx overlayers under DRM reaction conditions (CO2/CH4 = 1/1), which prevents the interaction between the reactants and metal centers for causing rapid deactivation. By increasing the partial pressure of CO2 (CO2/CH4 = 3/1), Rh/BN exhibits significantly enhanced activity and long-term stability in the DRM reaction. CO2 or H2O in the reactive atmosphere can effectively etch the BOx overlayers for steadily exposing the active Rh-BN interface sites, as evidenced by the characterization. This observation extends the understanding of the SMSI effect at the interfaces between metal and non-oxide support.

Insight into the Dynamic Evolution of Supported Metal Catalysts by In Situ/Operando Techniques and Theoretical Simulations

Insight into the Dynamic Evolution of Supported Metal Catalysts by <i>In Situ/Operando</i> Techniques and Theoretical Simulations

The resin-supported iron-copper bimetallic composite as highly active heterogeneous Fenton-like catalysts for degradation of gaseous toluene.

In this study, a resin-supported iron-copper bimetallic heterogeneous Fenton catalyst with excellent removal performance, superior economy and outstanding recoverability was synthesized by an impregnation method and used to remove gaseous toluene. Experiments disclosed that 3-FeCu@LXQ-10 possessed extremely high catalytic capacity. At a temperature of 30 °C, an initial toluene concentration of 200 mg/m3 and H2O2 atomization amount of 3 mmol/h, the toluene removal efficiency of 3-FeCu@LXQ-10 was 97.50%. Experimental tests had revealed that the bimetallic supported catalysts exhibited higher catalytic activity than single metal-supported catalysts, owing to an interaction effect between iron and copper metal ions. Furthermore, electron paramagnetic resonance (EPR) and radical quenching tests were carried out, and the results indicated •OH radicals performed a key role in the Fenton-like process. In addition, the iron-copper bimetallic catalysts exhibited good reusability and stability characteristics during six degradation cycles. This study shows promising potential in using FeCu@LXQ-10 as a heterogeneous catalyst for removing toluene.

Identifying the Structure of Supported Metal Catalysts Using Vibrational Fingerprints from Ab Initio Nanoscale Models (Small 34/2023)

Identifying the Structure of Supported Metal Catalysts Using Vibrational Fingerprints from Ab Initio Nanoscale Models (Small 34/2023)

Elucidating the Structure and Composition of Individual Bimetallic Nanoparticles in Supported Catalysts by Atom Probe Tomography.

Understanding and controlling the structure and composition of nanoparticles in supported metal catalysts are crucial to improve chemical processes. For this, atom probe tomography (APT) is a unique tool, as it allows for spatially resolved three-dimensional chemical imaging of materials with sub-nanometer resolution. However, thus far APT has not been applied for mesoporous oxide-supported metal catalyst materials, due to the size and number of pores resulting in sample fracture during experiments. To overcome these issues, we developed a high-pressure resin impregnation strategy and showcased the applicability to high-porous supported Pd-Ni-based catalyst materials, which are active in CO2 hydrogenation. Within the reconstructed volume of 3 × 105 nm3, we identified over 400 Pd-Ni clusters, with compositions ranging from 0 to 16 atom % Pd and a size distribution of 2.6 ± 1.6 nm. These results illustrate that APT is capable of quantitatively assessing the size, composition, and metal distribution for a large number of nanoparticles at the sub-nm scale in industrial catalysts. Furthermore, we showcase that metal segregation occurred predominately between nanoparticles, shedding light on the mechanism of metal segregation. We envision that the presented methodology expands the capabilities of APT to investigate porous functional nanomaterials, including but not limited to solid catalysts.

Theoretical insight into the promotion effect of potassium additive on the water-gas shift reaction over low-coordinated Au catalysts.

How to elucidate the effect of alkali metal promoters on gold-catalyzed water-gas shift reaction intrinsically remains a challenging, because that the complex synergy effects such as strong metal-support interactions, interfacial effects, and charge transfer of supported metal catalysts makes people difficulty in the understanding the alkali promotion phenomenon in nature. Herein, we report a systematically study of whole water-gas shift reaction mechanism on pure and the K-modified defected-Au(211) (i.e., by removing one surface Au atom from perfect Au(211) and make one model with the Au-Au coordination number is six) by using the microkinetic modeling based on first principles. Our results indicate that the presence of K can increase the adsorption ability of oxygen-containing species via the attractive coulomb interaction, has no significant effect on the adsorption of H species, but inhibits the adsorption of CO due to the steric effect. K promoter stabilizes the water adsorption by ~0.3 eV, which results in one order increasing of whole reaction rate. Interestingly, the strong promotion effect of the K can be assigned to the significant direct space interaction between K and the adsorbate H2O* through the inducted electric field, which can be further confirmed by the posed negative electric field on the unpromoted D-Au(211). Microkinetic modeling results revealed that the carboxyl mechanism is the most likely to occur, redox mechanism is the next one, and the formate mechanism is the least likely to occur. For different kinds of alkali metal additives, the adsorption strength of water molecules gradually weakens from Li to Cs, but Na shows the best promoter behavior at the low temperature. By considering the effect of K contents on the reactivity of water-gas shift reaction, we found that the K with the medium coverage (~0.2~0.3 ML) has the strongest promoting effect. It is expected that the conclusion of this work can be extended to other WGSR catalytic systems like Cu(or Pt). All calculations were performed by using the plane-wave based periodic method implemented in Vienna ab initio simulation package (VASP, version 5.4.4), where the ionic cores are described by the projector augmented wave (PAW) method. The exchange and correlation energies were computed using the Perdew, Burke and Ernzerhof functional with the vdw correction (PBE-D3). The transition states (TSs) were searched using the climbing image nudged elastic band (CI-NEB) method. Some electronic structure properties like work function was predicated by the DS-PAW software. Microkinetic simulation was carried out using MKMCXX software.