Surface Catalytic Reactions Research Articles

Plasmonic Photoelectrochemical Coupling Reactions of para-Aminobenzoic Acid on Nanostructured Gold Electrodes.

Surface plasmon resonance (SPR) bridges photonics and photoelectrochemistry by providing an effective interaction between absorption and confinement of light to surface electrons of plasmonic metal nanostructures (PMNs). SPR enhances the Raman intensity enormously in surface-enhanced Raman spectroscopy (SERS) and leads to the plasmon-mediated chemical reaction on the surface of nanostructured metal electrodes. To observe variations in chemical reactivity and selectivity, we studied the SPR photoelectrochemical reactions of para-aminobenzoic acid (PABA) on nanostructured gold electrodes. The head-to-tail coupling product "4-[(4-imino-2,5-cyclohexadien-1-ylidene)amino]benzoic acid (ICBA)" and the head-to-head coupling product p,p'-azodibenzoate (ADBA) were obtained from PABA adsorbed on PMN-modified gold electrodes. In particular, under acidic and neutral conditions, ICBA was obtained as the main product, and ADBA was obtained as the minor product. At the same time, under basic conditions, ADBA was obtained as the major product, and ICBA was obtained as the minor product. We have also provided sufficient evidence for the oxidation of the tail-to-tail coupling reaction product that occurred in a nonaqueous medium rather than in an aqueous medium. The above finding was validated by the cyclic voltammetry, SERS, and theoretical calculation results of possible reaction intermediates, namely, 4-aminophenlylenediamine, 4-hydroxyphenlylenediamine, and benzidine. The theoretical adsorption model and experimental results indicated that PABA has been adsorbed as para-aminobenzoate on the gold cluster in a bidentate configuration. This work offers a new view toward the modulation of selective surface catalytic coupling reactions on PMN, which benefits the hot carrier transfer efficiency at photoelectrochemical interfaces.

Coupling mesoscale transport to catalytic surface reactions in a hybrid model.

In heterogeneous catalysis, reactivity and selectivity are not only influenced by chemical processes occurring on catalytic surfaces but also by physical transport phenomena in the bulk fluid and fluid near the reactive surfaces. Because these processes take place at a large range of time and length scales, it is a challenge to model catalytic reactors, especially when dealing with complex surface reactions that cannot be reduced to simple mean-field boundary conditions. As a particle-based mesoscale method, Stochastic Rotation Dynamics (SRD) is well suited for studying problems that include both microscale effects on surfaces and transport phenomena in fluids. In this work, we demonstrate how to simulate heterogeneous catalytic reactors by coupling an SRD fluid with a catalytic surface on which complex surface reactions are explicitly modeled. We provide a theoretical background for modeling different stages of heterogeneous surface reactions. After validating the simulation method for surface reactions with mean-field assumptions, we apply the method to non-mean-field reactions in which surface species interact with each other through a Monte Carlo scheme, leading to island formation on the catalytic surface. We show the potential of the method by simulating a more complex three-step reaction mechanism with reactant dissociation.

The Inorganic Perovskite-Catalyzed Transfer Hydrogenation of Cinnamaldehyde Using Glycerol as a Hydrogen Donor

Catalytic transfer hydrogenation reactions (CTHs) produce value-added chemicals in the most economical, safe, green, and sustainable way. However, understanding the reaction mechanism and developing stable, selective, and cheap catalysts has been a significant challenge. Herein, we report on the hydrogenation of cinnamaldehyde utilizing glycerol as a hydrogen donor and metal-oxides (SnO2, LaFeO3, and LaSnO3) as heterogeneous catalysts. The perovskite types were used because they are easy to synthesize, the metal components are readily available, and they are good alternatives to noble metals. The catalysts were synthesized through the nanocasting (hard-template) method with SiO2 (KIT-6) as a template. The template was synthesized using the soft-template (sol-gel) method resulting in a high surface area of 624 m2/g. Furthermore, catalytic evaluations gave high cinnamaldehyde percentage conversions of up to 99%. Interestingly, these catalysts were also found to catalyze the etherification of glycerol in one pot. Therefore, we propose competitive surface catalytic reactions driven by the transition metal cations as the binding sites for the cinnamaldehyde and the sacrificial glycerol.

Unveiling the effect of interstitial dopants on CO2 activation over CsPbBr3 catalyst for efficient photothermal CO2 reduction

Halide perovskites, enabled by their superior light harvesting ability and high carrier mobility, have emerged as promising catalysts for solar CO2 reduction. However, the catalytic performance remains largely limited due to the challenge of efficient CO2 activation on pristine perovskite surface. Herein, we elaborately doped the CsPbBr3 with interstitial Cu ions to reveal the effect of dopants on the CO2 activation for photothermal CO2 reduction using H2O as the proton source. Initially, the interstitial Cu dopants would significantly suppress the charge carrier recombination in CsPbBr3, leaving more carriers to participate in the surface catalytic reactions. Meanwhile, the Cu dopants would modulate the surface sites for better adsorption and activation of CO2 molecules and CO intermediates, as evidenced by the results of CO2 and CO temperature-programed-desorption profiles. Furthermore, analysis of in-situ diffuse-reflectance infrared Fourier transform spectra (DRIFTS) and theoretical calculations indicates that the CO2 reduction to CH4 follows *COH pathway on Cu:CsPbBr3, but *CHO pathway on CsPbBr3, where the former is more thermodynamically favorable. It is then revealed that the Cu dopants would facilitate the CO2 reduction by supplying more carriers, adsorbing more CO2 molecules and catalyzing the CO2 dissociation more easily. As a result, our Cu:CsPbBr3 achieved an impressive activity of 14.72 μmol·g−1·h−1 for CH4 production and a CH4 selectivity of 96.9%, which are both higher than those of the pristine CsPbBr3 (3.62 μmol·g−1·h−1 and 81.1%). Our work provides an insightful understanding of the roles of dopants in the CO2 activation for photothermal catalytic CO2 reduction on halide perovskite catalysts.

Negative inductive effect enhances charge transfer driving in sulfonic acid functionalized graphitic carbon nitride with efficient visible-light photocatalytic performance

Efficient photogenerated carrier migration/separation plays a critical role in increasing the photocatalytic performance of g-C3N4. Herein, sulfonic acid group-functionalized g-C3N4 (SACN) was synthesized and then synchronously strengthened by a facile-solid-state thermal reaction of g-C3N4 and sulfamic acid. As a solid strong acid, sulfamic acid can be used to achieve acid etching on the surface of g-C3N4 with the assistance of thermal treatment, leading to an enlarged specific surface area and increased surface catalytic reaction sites. More importantly, our experiments and density functional theory calculations indicate that the driving force generated by the negative inductive effect of sulfonic acid groups significantly improves the charge transfer dynamics and effectively inhibits their recombination. Moreover, the negative inductive effect can induce charge redistribution, which reduces the conduction band potential of g-C3N4 to enhance the reduction ability of photo-induced electrons. As a result, the SACN-400 sample showed excellent photocatalytic performance in H2 generation with an apparent quantum efficiency of 11.03% at 420 ± 15 nm, as well as an efficient photodegradation rate for organic pollutants.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products.

The generation of multi-carbon products on the Cu2O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO2 reduction through plasmon metal (Ag) decoration on Cu2O nanowires. The Cu2O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH3COOH and the generation rate is 212.7 μmol cm-2 h-1 under illumination, which is about five times that in dark (44.4 μmol cm-2 h-1) at -0.7 V vs. RHE.

Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts.

The conversion and storage of solar energy to chemical energy via artificial photosynthesis holds significant potential for optimizing the energy situation and mitigating the global warming effect. Photocatalytic water splitting utilizing particulate semiconductors offers great potential for the production of renewable hydrogen, while this cross-road among biology, chemistry, and physics features a topic with fascinating interdisciplinary challenges. Progress in photocatalytic water splitting has been achieved in recent years, ranging from fundamental scientific research to pioneering scalable practical applications. In this review, we focus mainly on the recent advancements in terms of the development of new light-absorption materials, insights and strategies for photogenerated charge separation, and studies towards surface catalytic reactions and mechanisms. In particular, we emphasize several efficient charge separation strategies such as surface-phase junction, spatial charge separation between facets, and polarity-induced charge separation, and also discuss their unique properties including ferroelectric and photo-Dember effects on spatial charge separation. By integrating time- and space-resolved characterization techniques, critical issues in photocatalytic water splitting including photoinduced charge generation, separation and transfer, and catalytic reactions are analyzed and reviewed. In addition, photocatalysts with state-of-art efficiencies in the laboratory stage and pioneering scalable solar water splitting systems for hydrogen production using particulate photocatalysts are presented. Finally, some perspectives and outlooks on the future development of photocatalytic water splitting using particulate photocatalysts are proposed.

Machine learning the quantum flux–flux correlation function for catalytic surface reactions

Gaussian process regressors were successfuly trained to predict fully quantum flux–flux correlation functions and the corresponding reaction rate constants.

Catalytic resonance theory: Negative dynamic surfaces for programmable catalysts

Catalysts that change with time via programmed variation of their electronic occupation to accelerate surface reactions were evaluated in the case of negative adsorption energy scaling relations. Defined as the relative change in adsorption enthalpy, the gamma linear scaling parameter is negative when two adsorbates alternatively weaken and strengthen as catalysts are electronically perturbed. Simulations were conducted of a single transition state connecting two generic adsorbates representative of multiple reaction classes to understand the resulting negative gamma catalytic ratchet mechanism and its ability to accelerate catalytic reactions above the Sabatier peak and away from equilibrium. Relative to conventional positive gamma catalytic ratchets, the Sabatier volcanoes of negative gamma catalysis are narrower with greater enhancement of dynamic turnover frequency when catalysts are electronically oscillated. Promotion of the catalytic surface reaction forward or backward was predictable by a descriptor accounting for the relative rates of forward and reverse kinetics under oscillatory conditions. • Identified the most energy efficient negative dynamic reaction energy profile • Optimized negative scaling dynamic catalysts using their tunable design parameters • Developed a global descriptor to predict reaction selectivity at high conversion The emergence of low-cost solar and wind power requires new catalytic technologies that can achieve faster rates for hydrogen production and ammonia synthesis as a method for storing and moving renewable energy. These two important catalytic reactions are limited by the Sabatier principle, making them too slow by conventional static catalysis for small-scale implementation nearby distributed power sources. However, the application of dynamic programmable catalysts for these chemistries can accelerate the catalytic turnover frequency substantially above the Sabatier limitation. In particular, negative scaling relationships have been predicted for the synthesis of energy-dense liquids, and these negative gamma programmable catalysts achieve high efficiency in both rate acceleration and reaction promotion relative to energy input, making them ideal catalytic devices for energy intensive catalytic chemistry. The promotion of reactions using surfaces that change with time can be achieved with programmable surfaces that feature negative scaling relationships between the reactant and the product. These programmable surfaces exhibit unique catalytic behavior to accelerate reactions and push the extent of conversion away from equilibrium.

Identification and Design of Active Sites on Photocatalysts for the Direct Artificial Carbon Cycle

ConspectusImitating the natural carbon cycle, the utilization of the carbon-based greenhouse gases (i.e., carbon dioxide (CO2) and methane (CH4)) from the atmosphere as the carbon feedstocks for valuable fuel and chemical production represents a prospective strategy for achieving the sustainable development of human society. In light of this, photocatalytic CO2/CH4 conversions, which can directly harvest solar energy for the production of valuable fuels and chemicals, show gigantic potential for closing the loop of the artificial carbon cycle. In the past several decades, immense progress has been made in this field, showing its practical feasibility. However, the photocatalytic conversion efficiency and selectivity of such reactions remain discouraging. Considering that the photocatalytic reaction is intimately related to the surface catalytic reaction on the active sites of the photocatalysts, the active site design has been proven to be effective for optimizing photocatalytic performance, yet the lack of effective techniques for the identification of the active sites, which is normally at the molecular level, greatly limits its potential in photocatalysis. Fortunately, with the rapid expansion in the field of materials science, a large number of advanced characterization techniques have been developed, equipping the materials scientist and chemist with powerful tools for unveiling the mask of the active sites on the photocatalysts. Concomitantly, the active site design for the photocatalysts has undergone a revival. Today, the identification and design of active sites have emerged as hot topics in catalysis and are expected to push forward development in the field of the artificial carbon cycle.Herein, we highlight the recent progress of our research group in the identification and design of active sites for the direct artificial carbon cycle. We begin by giving an introduction to the advantages of the direct artificial carbon cycle over the indirect artificial carbon cycle. Then, we systematically describe the concept of active sites and requirements for the active sites toward highly efficient and selective photocatalytic CO2/CH4 conversion. Subsequently, we present an overview of the currently available characterization techniques and tools for identifying the active sites on the photocatalysts. Furthermore, we outline our group’s endeavor in designing the active sites for photocatalytic CO2/CH4 conversion. Finally, we conclude this Account by offering some comments on the current challenges and future perspectives in this field. We foresee that this Account not only summarizes the recent work of our group in this field but also can facilitate the development of the direct artificial carbon cycle.

Work function tuned, surface Cs intercalated BiVO4 for enhanced photoelectrochemical water splitting reactions

Monoclinic BiVO4 is a widely researched semiconductor in solar water splitting owing to its suitable characteristics. However, BiVO4 faces limitations, such as the inefficient separation and transportation of photogenerated charges in the bulk and poor catalytic water oxidation reactions at the surface that affect the water-splitting efficiency. In this work, the Cs intercalation strategy at the surface of BiVO4 is proposed for the enhanced water splitting to H2 and O2 productions via the effective separation and transportation photogenerated charges and improved surface catalytic water oxidation reactions. The Cs ions are found to intercalate at the surface of BiVO4 and regulate the oxygen vacancies to provide active O2 production sites and stability. The surface intercalation of Cs boosts the photocurrent to 1.89 mA cm−2 at 1.23 V vs. reference hydrogen electrode (RHE). A stoichiometric evolution of H2 and O2 is recorded with a faradaic efficiency of 92%. The open-circuit voltage measurements confirmed the increase in the carrier lifetime with the work function tuning upon Cs intercalation. The proposed Cs intercalation strategy suggests an effective route to suppress the charge recombination with an increase in carrier lifetime and charge separation in BiVO4 for the enhanced PEC application.

Novel Clarification of Surface Plasmon Coupling Reactions of Aromatic Alkynamine and Nitro Compounds

This work presents a theoretical and experimental approach for the coupling of 4-ethynylaniline (4-APA) and 4-ethynylnitrobenzene (4-NPA) in the theoretical application of density functional theory (DFT) and experimental monitoring of surface-enhanced Raman spectroscopy (SERS). The results support electromagnetic enhancement to drive the conversion of aromatic alkynamine and nitro compounds and regulation by the catalytic coupling reaction conditions. In addition, this work investigates the adsorption site effect of surface plasmon coupling reactions of 4-APA and 4-NPA molecules into alkynyl azo compounds. This study presents theoretical and experimental images used to analyze the plasmon-driven surface catalytic reaction system.

Consequences of adsorbate-adsorbate interactions for apparent kinetics of surface catalytic reactions

Lateral adsorbate interactions at catalyst surfaces are known to influence adsorption energies and reaction rates. Lattice-based kinetic Monte Carlo (kMC) simulations are able to capture these influences, but such models are typically parameterized for a specific reaction network and catalyst surface. Here we report kMC simulations to probe the influence of lateral interactions on simulated rates, rate orders, apparent activation energies, and Sabatier plots. We construct a simple, two-step reaction network involving a single adsorbate and rate-limiting diatomic dissociation, employ a generic repulsive lateral interaction model consistent with known adsorbate–adsorbate interactions on metal surfaces, and a rate model consistent with known Brønsted-Evans-Polyani relationships for diatomic dissocations. We juxtapose reaction kinetics over a wide range of reaction conditions and catalyst binding energies, as a function of interaction strength. We find that at a given zero-coverage binding energy and external conditions, adsorbate coverage decreases monotonically with increasing interaction strength, but absolute rates can vary linearly or nonlinearly. Interactions flatten the Sabatier volcano and shift the maximum towards stronger binding. Influences on apparent rate orders and activation energies are modest and are sensitive to interaction-induced adsorbate ordering. Model predictions are sensitive to lattice size effects at high coverages. The results, modelled for a simple reaction system, highlight the generic consequences of lateral interactions and guidance for identifying their signatures in observed kinetics.

Nanostructure Engineering via Intramolecular Construction of Carbon Nitride as Efficient Photocatalyst for CO2 Reduction.

Light-driven heterogeneous photocatalysis has gained great significance for generating solar fuel; the challenging charge separation process and sluggish surface catalytic reactions significantly restrict the progress of solar energy conversion using a semiconductor photocatalyst. Herein, we propose a novel and feasible strategy to incorporate dihydroxy benzene (DHB) as a conjugated monomer within the framework of urea containing CN (CNU-DHBx) to tune the electronic conductivity and charge separation due to the aromaticity of the benzene ring, which acts as an electron-donating species. Systematic characterizations such as SPV, PL, XPS, DRS, and TRPL demonstrated that the incorporation of the DHB monomer greatly enhanced the photocatalytic CO2 reduction of CN due to the enhanced charge separation and modulation of the ionic mobility. The significantly enhanced photocatalytic activity of CNU–DHB15.0 in comparison with parental CN was 85 µmol/h for CO and 19.92 µmol/h of the H2 source. It can be attributed to the electron–hole pair separation and enhance the optical adsorption due to the presence of DHB. Furthermore, this remarkable modification affected the chemical composition, bandgap, and surface area, encouraging the controlled detachment of light-produced photons and making it the ideal choice for CO2 photoreduction. Our research findings potentially offer a solution for tuning complex charge separation and catalytic reactions in photocatalysis that could practically lead to the generation of artificial photocatalysts for efficient solar energy into chemical energy conversion.

Consequences of adsorbate-adsorbate interactions for modelled reaction kinetics of surface catalytic reactions

Consequences of adsorbate-adsorbate interactions for modelled reaction kinetics of surface catalytic reactions

MoS2/graphene van der Waals heterojunctions combined with two-layered Au NP for SERS and catalysis analyse.

MoS2-plasmonic hybrid platforms have attracted significant interest in surface-enhanced Raman scattering (SERS) and plasmon-driven photocatalysis. However, direct contact between the metal and MoS2 creates strain that deteriorates the electron transport across the metal/ MoS2 interfaces, which would affect the SERS effect and the catalytic performance. Here, the MoS2/graphene van der Waals heterojunctions (vdWHs) were fabricated and combined with two-layered gold nanoparticles (Au NP) for SERS and plasmon-driven photocatalysis analyse. The graphene film is introduced to provide an effective buffer layer between Au NP and MoS2, which not only eliminates the inhomogeneous contact on MoS2 but also benefits the electron transfer. The substrate exhibits excellent SERS capability realizing ultra-sensitive detection for 4-pyridinethiol molecules. Also, the surface catalytic reaction of p-nitrothiophenol (PNTP) to p,p-dimercaptobenzene (DMAB) conversion was in situ monitored, demonstrating that the vdWHs-plasmonic hybrid could effectively accelerate reaction process. The mechanism of the SERS and catalytic behaviors are investigated via experiments combined with theoretical simulations (finite element method and quantum chemical calculations).

Buoyancy driven second grade nano boundary layers over a catalytic surface with reaction rate, heat of reaction and activation energy at boundary

The present article aims to explore the characteristics of catalytic surface reactions on free convection non-Newtonian nanofluid boundary layers which are driven by buoyancy force. The non-Newtonian behavior of the fluid is modeled using a Cauchy stress tensor which includes pressure, dynamic viscosity, two normal stress moduli and two Rivlin-Ericksen tensors. The Buongiorno model is utilized to model the nanofluid behavior. The exothermic surface reactions are considered by Arrhenius kinetics at the wall. The boundary conditions are designed with one-step, non-isothermal and first order reactions. Furthermore, the flow phenomenon is assumed with elastic deformation effects. To carry out a parametric study, the governing equations and boundary conditions were transformed into a non-dimensional form with essential parameters. The impacts of exothermic reactions in the flow region are explored using heat of reaction, reaction rate and activation energy parameters which occurred in the boundary. The flow behaviors are clearly analyzed with a numerical experiment. The results are plotted for momentum, thermal and concentration boundary layers, skin friction, dimensionless wall temperature and dimensionless wall concentration. The numerical values of dimensionless wall temperature and wall concentration are presented. It is found that the heat of reaction raises the temperature and concentration profiles significantly due to the catalytic surface reactions and it shows a slight enhancement in the velocity profile. Both activation energy and reaction rate constant retard all the nanofluid profiles and have a significant role on the temperature and concentration profiles. The surface reaction and the buoyancy parameters show a significant variation inside the boundary layer flow region of second grade nanofluid.

Boosting Photocatalytic Water Oxidation Over Bifunctional Rh0 -Rh3+ Sites.

Photocatalytic water splitting provides an economically feasible way for converting solar energy into hydrogen. Great efforts have been devoted to developing efficient photocatalysts; however, the surface catalytic reactions, especially for the sluggish oxygen evolution reaction (OER), still remain a challenge, which limits the overall photocatalytic energy efficiency. Herein, we design a Rhn cluster cocatalyst, with Rh0 -Rh3+ sites anchoring the Mo-doped BiVO4 model photocatalytic system. The resultant photocatalyst enables a high visible-light photocatalytic oxygen production activity of 7.11 mmol g-1 h-1 and an apparent quantum efficiency of 29.37 % at 420 nm. The turnover frequency (TOF) achieves 416.73 h-1 , which is 378 times higher than that of the photocatalyst only with Rh3+ species. Operando X-ray absorption characterization shows the OER process on the Rh0 -Rh3+ sites. The DFT calculations further illustrate a bifunctional OER mechanism over the Rh0 -Rh3+ sites, in which the oxygen intermediate attacks the Rh3+ sites with assistance of a hydrogen atom transfer to the Rh0 sites, thus breaking the scaling relationship of various oxygen intermediates.

Boosting Photocatalytic Water Oxidation Over Bifunctional Rh0‐Rh3+ Sites

AbstractPhotocatalytic water splitting provides an economically feasible way for converting solar energy into hydrogen. Great efforts have been devoted to developing efficient photocatalysts; however, the surface catalytic reactions, especially for the sluggish oxygen evolution reaction (OER), still remain a challenge, which limits the overall photocatalytic energy efficiency. Herein, we design a Rhn cluster cocatalyst, with Rh0‐Rh3+ sites anchoring the Mo‐doped BiVO4 model photocatalytic system. The resultant photocatalyst enables a high visible‐light photocatalytic oxygen production activity of 7.11 mmol g−1 h−1 and an apparent quantum efficiency of 29.37 % at 420 nm. The turnover frequency (TOF) achieves 416.73 h−1, which is 378 times higher than that of the photocatalyst only with Rh3+ species. Operando X‐ray absorption characterization shows the OER process on the Rh0‐Rh3+ sites. The DFT calculations further illustrate a bifunctional OER mechanism over the Rh0‐Rh3+ sites, in which the oxygen intermediate attacks the Rh3+ sites with assistance of a hydrogen atom transfer to the Rh0 sites, thus breaking the scaling relationship of various oxygen intermediates.

Crystallographic facet heterojunction of MIL-125-NH2(Ti) for carbon dioxide photoreduction

Facet exposure affects photocatalytic CO2 reduction reaction, but the insight remains unclear. Here, we report finely controlled six types of MIL-125-NH2(Ti) exposing single and co-exposing mixed low-index facets as model catalysts and provide an insight into facet effect on photoreduction of CO2. Facet surface heterojunction endows MIL-125-NH2(Ti) with a broadened light-absorption and accelerated charge migration. The MIL-125-NH2(Ti) with {110}/{111}-heterojunction yields ca. 10 and 18 times enhanced CO2 reduction to CO and CH4 compared with the single {001} facet exposed. Density functional theory (DFT) calculations provide an energetically favorable CO2 catalytic reduction pathway and identify the rate-limiting step on different low-index facets. This work aims at exploring facet-effect on CO2 photoreduction, understanding the facet-dependence and providing a paradigm for MOFs materials by regulating facet to enhance the general surface catalytic reaction activity.