Heterogeneous Catalytic System Research Articles

Catalytic CO2 conversion to C1 value-added products: Review on latest catalytic and process developments

With the increase in CO2 emissions in the last decades, CO2 capture and storage and CO2 capture and utilization technologies have been interesting topics in literature and industry. CO2 direct utilization for oil gas recovery is a mature utilization route in the oil and gas industry. CO2 is the focus of many technological and academic studies for its potential as a source of carbon for producing value-added chemical products and synthetic fuels. CO2 utilization technologies are grouped based on the production route, such as electrochemical, catalytic, photocatalytic, photosynthetic, biological, and depolymerization. This review discusses the latest technological innovations in catalyst developments for direct CO2 utilization to C1 value-added products and fuels. Amongst the various potential products, CO2 conversion to dimethyl carbonates, methanol, formic acid, syngas, and methane using different homogenous and heterogeneous catalytic systems was discussed. The most recent advancements for process exploitations were highlighted for each utilization route to evaluate the maturity of the proposed systems technically and economically. The review revealed that thermally-driven CO2 catalytic conversion to methanol, synthesis gas and methane are the most promising for industrial deployment. Furthermore, Green hydrogen and the cost of energy production are the key obstacles to large-scale deployments of CO2 utilization. However, supported by the latest advancements in renewable energy production, the discussed utilization routes would be more applicable in the near future.

An Efficient Continuous Flow Synthesis for the Preparation of N-Arylhydroxylamines: Via a DMAP-Mediated Hydrogenation Process.

The selective hydrogenation of nitroarenes to N-arylhydroxylamines is an important synthetic process in the chemical industry. It is commonly accomplished by using heterogeneous catalytic systems that contain inhibitors, such as DMSO. Herein, DMAP has been identified as a unique additive for increasing hydrogenation activity and product selectivity (up to >99%) under mild conditions in the Pt/C-catalyzed process. Continuous-flow technology has been explored as an efficient approach toward achieving the selective hydrogenation of nitroarenes to N-arylhydroxylamines. The present flow protocol was applied for a vast substrate scope and was found to be compatible with a wide range of functional groups, such as electron-donating groups, carbonyl, and various halogens. Further studies were attempted to show that the improvement in the catalytic activity and selectivity benefited from the dual functions of DMAP; namely, the heterolytic H2 cleavage and competitive adsorption.

Metal-Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical-Mediated Reactions.

Visible-light copper photocatalysis has recently emerged as a viable technology for building sustainable synthetic processes. To broaden the applications of phosphine-ligated copper(I) complexes, we describe herein an effective metal-organic framework (MOF)-supported copper(I) photocatalyst for multiple iminyl radical-mediated reactions. Due to site isolation, the heterogenized copper photosensitizer has a significantly higher catalytic activity than its homogeneous counterpart. Using a hydroxamic acid linker to immobilize copper species on MOF supports affords the heterogeneous catalysts with high recyclability. The post-synthetic modification sequence on MOF surfaces allows for the preparation of previously unavailable monomeric copper species. Our findings highlight the potential of using MOF-based heterogeneous catalytic systems to address fundamental challenges in the development of synthetic methodologies and mechanistic investigations of transition-metal photoredox catalysis.

Metal‐Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical‐Mediated Reactions

AbstractVisible‐light copper photocatalysis has recently emerged as a viable technology for building sustainable synthetic processes. To broaden the applications of phosphine‐ligated copper(I) complexes, we describe herein an effective metal‐organic framework (MOF)‐supported copper(I) photocatalyst for multiple iminyl radical‐mediated reactions. Due to site isolation, the heterogenized copper photosensitizer has a significantly higher catalytic activity than its homogeneous counterpart. Using a hydroxamic acid linker to immobilize copper species on MOF supports affords the heterogeneous catalysts with high recyclability. The post‐synthetic modification sequence on MOF surfaces allows for the preparation of previously unavailable monomeric copper species. Our findings highlight the potential of using MOF‐based heterogeneous catalytic systems to address fundamental challenges in the development of synthetic methodologies and mechanistic investigations of transition‐metal photoredox catalysis.

Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts.

CuFe2O4/diatomite actuates peroxymonosulfate activation process: Mechanism for active species transformation and pesticide degradation

Peroxymonosulfate (PMS) activation is a promising technology for water purification, but the removal performance of multiple pollutant matrices and the mechanism for reactive species transformation in the heterogeneous catalytic system remain ambiguous. Herein, a novel CuFe2O4/diatomite was fabricated for PMS activation to achieve efficient removal of typical pesticides. Uniform distribution of CuFe2O4 on diatomite efficiently alleviated the agglomeration of CuFe2O4 and increased specific surface area (57.20 m2 g−1, 3.8-fold larger than CuFe2O4). CuFe2O4/5% diatomite (5-CFD)/PMS system showed nearly 100% removal efficiency for mixed pesticide solution within 10 min (0.10 g L−1 5-CFD and 0.40 g L−1 PMS) and excellent anti-interference performance towards various coexisting substances (≥90% removal efficiency). The electrochemical measurements confirmed that the lower charge transfer resistance of 5-CFD significantly enhanced the electron-transfer capacity between 5-CFD and PMS, accelerating the reactions among Fe(III)/Fe(II), Cu(II)/Cu(I), and PMS, further generating •OH (261.3 μM), 1O2 (138.8 μM), SO4•– (11.8 μM), and O2•–. The O in reactive oxygen species didn't originate from dissolved oxygen (DO) but PMS, independent of the low solubility of DO and slow diffusion rate of O2 in water. Furthermore, the production of 1O2 went through the process: PMS → O2•– → 1O2, and SO4•– could rapidly convert into •OH. The degradation pathways and the evolution of intermediates were proposed by HPLC-QTOF-MS/MS and DFT calculations. QSAR analysis illustrated that the toxicity became lower with the reaction process. This study provides novel insights into the mechanism for pesticide degradation and active species transformation and the anti-interference capability of systems.

Reduction of Nitrous Oxide by Light Alcohols Catalysed by a Low-Valent Ruthenium Diazadiene Complex.

Decomposition of the environmentally harmful gas nitrous oxide (N2 O) is usually performed thermally or catalytically. Selective catalytic reduction (SCR) is currently the most promising technology for N2 O mitigation, a multicomponent heterogeneous catalytic system that employs reducing agents such as ammonia, hydrogen, hydrocarbons, or a combination thereof. This study reports the first homogenous catalyst that performs the reduction of nitrous oxide employing readily available and cheap light alcohols such as methanol, ethanol or ethylene glycol derivatives. During the reaction, these alcohols are transformed in a dehydrogenative coupling reaction to carboxylate derivatives, while N2 O is converted to N2 and H2 O, later entering the reaction as substrate. The reaction is catalysed by the low-valent dinuclear ruthenium complex [Ru2 H(μ-H)(Me2 dad)(dbcot)2 ] that carries a diazabutadiene, Me2 dad, and two rigid dienes, dbcot, as ligands. The reduction of nitrous oxide proceeds with low catalyst loadings under relatively mild conditions (65-80 °C, 1.4 bar N2 O) achieving turnover numbers of up to 480 and turnover frequencies of up to 56 h-1 .

Waste-minimized C(sp3)-H activation for the preparation of fused N-heterocycles

By exploiting the combined use of a heterogeneous recyclable palladium(II)-bis(N-heterocyclic carbene) catalyst and cyclopentyl methyl ether (CPME) as a convenient recoverable safer reaction medium, an effective waste-minimized approach has been developed for the intramolecular Pd-catalyzed C(sp3)-H activation of methyl pyrrole derivatives. This synthetic tools has allowed to access condensed N-heterocycles generally endowed with biological activities and representatively are the core motif of complex molecules such as Mitomycines and Tylophorines. The heterogeneous catalytic system could be recovered and reused up to representative five runs without any loss in efficiency. The target products (19 examples) have been obtained selectively and with excellent isolated yields up to 93%. The approach leads to the definition of a protocol with a very good E-factor (21) which is much lower (up to 98%) than those of comparable literature examples. Other green metrics have been calculated and the data collected demonstrate that our newly developed protocol is very promising in terms of its environmental impact profile.

Green and Efficient Acquirement of Unsaturated Ether from Direct and Selective Hydrogenation Coupling Unsaturated Aldehyde with Alcohol by Bi-Functional Al-Ni-P Heterogeneous Catalysts

In view of the industrial importance of high-grade unsaturated ether (UE) and the inconvenience of acquiring the compound, herein, a series of low-cost Al-Ni-P catalysts in robust AlPO4/Ni2P structure possessing novel bi-functional catalytic features (hydrogenation activation and acid catalysis) were innovated, and testified to be efficient for directly synthesizing UE with a superior yield up to 97% from the selective hydrogenation coupling carbonyl of unsaturated aldehyde (cinnamaldehyde or citral) with C1–C5 primary or secondary alcohol under 0.1 MPa H2 and 393 K. The integrated advantages of high efficiency, green manner and convenient operation of the present heterogeneous catalytic system gave the system potential for feasibly harvesting high-grade unsaturated ether in related fine chemical synthesis networks.

A Novel Insight into the Ullmann Homocoupling Reactions Performed in Heterogeneous Catalytic Systems.

The Ullmann reaction has been reported to be the first cross-coupling reaction performed by using a transition metal catalyst. This reaction has been initially considered as the copper-catalyzed homocoupling of aryl halides, leading to the formation of symmetrical biaryl compounds via the generation of novel C-C bonds. Although this reaction has been extensively studied in recent decades and valuable results have been achieved, there are still considerable efforts focused on the development of novel catalytic systems, mild reaction conditions, and extended substrate scope. The mechanistic aspects of the Ullmann homocoupling reaction have also been investigated, as related to the introduction of new sustainable strategies and green procedures. The application of recyclable heterogeneous catalysts has been found to overcome most of the limitations associated with the harsh reaction conditions of the original Ullmann reaction. More recently, copper-based catalytic systems have also been replaced by palladium nanoparticles, ionic palladium species, gold nanoparticles, and palladium-gold bimetallic systems. In this review, current results reported on the Ullmann homocoupling reaction are discussed, with an emphasis on the development of novel catalytic systems, which can be efficiently used under heterogeneous conditions.

Metal-free catalytic systems based on imidazolium chloride and strong bases for selective oxidative esterification of furfural to methyl furoate

Homogeneous and heterogeneous catalytic systems based on 1-benzyl-3-methylimidazolium chloride (BzmimCl) assisted by strong bases (Cs2CO3 or 1, 8-diazabicyclo [5.4.0] under-7-ene (DBU)) were applied in the oxidative esterification of furfural, to obtain 2-methyl-furoate (MF). The reaction was carried out in one step, using oxygen as a unique source of oxidation and methanol as an esterification reagent. Commercial BzmimCl was used as a homogeneous ionic catalyst whereas the heterogeneous ionic one (HCP-BzmimCl) was prepared through a Friedel-Crafts reaction between biphenyl and BzmimCl.The catalytic systems here reported yield MF with a selectivity > 92% and furfural conversions > 82% after 24 h. The homogeneous catalyst systems have better catalytic activity than the similar ionic liquid systems assisted by bases published so far. Besides, HCP-BzmimCl is the first heterogeneous metal-free catalyst containing imidazole chloride groups for this reaction. HCP-BzmimCl can be recycled up to 5 times using both bases, obtaining quantitatively methyl furoate.

Synergism of adsorption and ROS-dominated catalytic oxidation in activating peroxymonosulfate by magnetic hybrid MOFs for selective removal of organophosphorus pesticides

Selective removal organic pollutants using heterogeneous catalytic system via peroxymonosulfate (PMS) activation has drawn intensive interest in water purification. Herein, a core–shell magnetic composite (MZU) having a double-layer of two kinds of MOFs (ZIF-67 and UiO-66) was prepared with Fe3O4 as the core. To present the selective removal of organophosphorus pesticides (OPPs), phenylphosphonic acid (PPOA) was selected as the target pollutant and its removal rate by MZU/PMS system achieved near 100 % within 30 min. The resultant MZU exhibited robust activation of PMS with reactive oxygen species (ROS) including SO4−, OH and 1O2, and efficient adsorption performance for produced phosphate during the degradation process. Attractively, the degradation rate constant of PPOA was significantly higher than that of the other five OPPs in a mixed solution, depending on the strong interaction between PPOA and MZU. This study constructs a fascinating strategy with efficient synergy adsorption and PMS-activation for selective removal of target pollutants in a complex water system.

Bisphenol A removal in treated wastewater matrix at neutral pH using magnetic graphite intercalation compounds as persulfate activators.

Effluents of municipal wastewater treatment plants (WWTPs) are major sources for releasing contaminants of emerging concern (CECs) into the aquatic environment, which can result in negative effects on aquatic ecosystems and, as a consequence, on humans. Herein, the graphite intercalation concept was used to synthesize heterogeneous catalysts to degrade bisphenol A (BPA) as a model CEC in municipal WWTP effluents at neutral pH. The catalyst was synthesized using the simple molten salt method and showed several benefits, such as iron leaching prevention and stability in environmental matrices. Different methods were applied to describe the catalyst's structural characteristics. The proposed system removed 99.3% of BPA in 75 min using 2 g/L of the synthesized catalyst and 1.19 g/L (5 mM) persulfate at neutral pH. Quenching experiments showed that catalytic activities and BPA removals were significantly aided by both radical and non-radical pathways through the generation of free radicals and singlet oxygen (1 O2 ). Furthermore, the reuse of recycled synthesized catalyst was investigated on treated urban wastewater, and the results showed that the catalyst could degrade BPA from the wastewater in consecutive cycles, demonstrating its applicability under real conditions. PRACTITIONER POINTS: BPA was effectively removed from the effluents of municipal WWTPs at neutral pH. A new catalyst (magnetic GIC) was fabricated for heterogeneous catalytic systems. The catalyst activates persulfate to generate free radicals and 1 O2 , indicating that radical and non-radical pathways contribute to BPA degradation. The catalyst showed the ability to remove BPA even in the sixth cycle of use, demonstrating its stability and reusability.

Facile integration of hydroxyl ionic liquid into Cr-MIL-101 as multifunctional heterogeneous catalyst for promoting the efficiency of CO2 conversion

Rational integration of functional ionic liquids (ILs) into metal-organic frameworks (MOFs) is an intriguing and challenging strategy for design of fully heterogeneous catalytic systems for the synthesis of cyclic carbonates from cycloaddition of CO2 and epoxides. This study demonstrates a facile and versatile post-synthetic modification approach for incorporating hydroxyl-functionalized imidazolium IL into Cr-MIL-101 (HImBr@Cr-MIL-101) via coordinative bonding interaction between Cr CUS (coordinative unsaturated metal sites) in MOF and electron-rich –SH group in IL. The resultant HImBr@Cr-MIL-101 possesses high surface area, profitable porosity and good CO2 adsorption capacity, rendering it as an efficient heterogeneous catalyst for the cycloaddition reaction under co-catalyst and solvent free conditions. Compared to either pure Cr-MIL-101 or hydroxyl IL, HImBr@Cr-MIL-101 shows largely enhanced catalytic activity, attributing to the synergistic effect of the integrated multiple active sites, involving Cr CUS as Lewis acid, hydroxyl group as hydrogen bond donor, and bromide anion as nucleophilic reagent for ring-opening of epoxide, as well as tertiary N atom as Lewis basic site for activating CO2. This is also evidenced by the activation energy Ea catalyzed by the Cr-MIL-101-based catalysts with different functions. Notably, HImBr@Cr-MIL-101 also significantly outperforms other benchmark MOF-based catalysts. Moreover, benefited from the superb coordinative bonding interaction of the built Cr (III)–S bond, this catalyst exhibits good chemical stability and recyclability, which can be reused for at least seven runs without obvious catalytic activity depletion. This work provides a promising strategy for constructing multifunctional heterogeneous catalyst for CO2 cycloaddition reaction by highlighting the synergistic effect enabled by one host.

Controlling the reactions of free radicals with metal-radical interaction

Radicals are key intermediates in numerous reactions. Their high reactivity enables various transformations to occur under mild conditions, however, also brings great challenges to control their reactions especially over heterogeneous catalysts. Here we propose to use metal nanoparticles to directly steer the conversion of free radical species. Results from photocatalytic reactions, in situ transient absorption spectroscopy, and theoretical simulation demonstrate that supported Pd nanoparticles can efficiently stabilize free radical species generated from photo-excited TiO2, and thus manipulate their conversion on catalyst surface, owing to the enhanced electronic interactions between metal and radical species. These understandings are crucial for the design of advanced heterogeneous catalytic systems with controllable radical reactions.

Al–Fe pillared bentonite−Fe3O4–CaO2 nanocomposite for efficient adsorption and degradation of trichloroethylene

The agglomeration of magnetic nanoparticles significantly affects their catalytic efficiency, and the reduction of oxidant dosage is crucial for the practical application of heterogeneous catalysis from the perspective of cost and environmental friendliness. Al–Fe pillared bentonite−Fe3O4–CaO2 nanocomposite (PB@Fe3O4–CaO2) was synthesized in this study to form a heterogeneous catalytic system, and trichloroethylene (TCE) was used as the target contaminant because of its universality and volatility. The adsorption of TCE in the PB@Fe3O4–CaO2 system reached 63.9% under the condition of release inhibition of H2O2 from CaO2, and the value decreased to 28.2% and 29.8% under conditions favoring H2O2 release owing to the efficient catalytic degradation of TCE (68.0% and 65.4%, respectively). A higher systematic pH would result in a significant decrease in the TCE removal efficiency in the PB@Fe3O4–CaO2 system owing to the decrease in the yield of H2O2 and the tendency toward O2 generation. The co-existing inorganic anions and cations also resulted in a decrease in the efficiency of TCE removal, which was attributed to the generation of weak free radicals and promote the aggregation of the catalyst, respectively. Although the adsorption effect was 50.9% for TCE removal in actual groundwater, the degradation efficiency of TCE in the PB@Fe3O4–CaO2 system (41.9%) was approximately the same as that of the PB@Fe3O4/H2O2 system (40.9%) considering TCE volatilization. This research provides a material for the efficient adsorption and degradation of trichloroethylene without the need for the exogenous addition of oxidants.

Steady-state equation of thermal explosion in a distributed activation energy medium: numerical solution and approximations

This work presents a mathematical model of thermal explosion in a medium described by a Gaussian distribution of reactivity, along with the determination of critical values for model parameters and their dependence on the distribution dispersion. The numerical solution of boundary value problems for steady-state temperature distribution in a reaction medium (a sweep method along with the iterative refinement of a source function, a half-interval method to find the critical value of the Frank-Kamenetskii parameter) was used. The grid convergence was investigated for the used difference scheme; the first order of accuracy was observed as a result of numerical evaluation of the critical value of the Frank-Kamenetskii parameter. Calculations were carried out with accuracy to three decimal places. Numerical methods were implemented as programs in the MATLAB environment. Numerical approximations were obtained for solutions of the thermal explosion equation characterised by distributed activation energy in the quasi-steady-state approximation. It was shown that the critical value of the Frank-Kamenetskii parameter is associated with the dispersion of the distribution and the Arrhenius parameter by a simple approximate analytical formula, confirmed by comparing with numerical estimates. Since the dependence of the critical value of the Frank-Kamenetskii parameter on the dispersion is described by a Gaussian function, the reaction medium becomes thermally unstable even at small values of the distribution dispersion. Calculations showed that a significant dispersion of reactivity (on the order of tenths of the average) can be observed only for chemical reactions characterised by low sensitivity to temperature (i.e. a small heat effect or low activation energy). Approximate formulas for critical conditions were also obtained for asymmetrical distribution functions. The analysis allows the proposed mathematical model to be used for assessing the thermal stability of reactive media having distributed reactivity (for example, natural materials, polymers, heterogeneous catalytic systems, etc.).

A multi-faceted structural, thermodynamic, and spectroscopic approach for investigating ethanol dehydration over transition phase aluminas.

Understanding the role that the surface of a material plays in the mediation of a chemical reaction at the atomic level is paramount to the optimization and improvement of catalytic materials. While this area of research has matured over several decades, few techniques are sensitive enough to directly examine and differentiate the behavior of molecular adsorbates during the course of the chemical reaction with a substrate. In this study, a combined approach which involves structural characterization techniques, volumetric adsorption, temperature programmed desorption, and inelastic neutron scattering (INS) was used to investigate the mechanism of ethanol dehydration on the surface of transition phase aluminas. The alumina samples employed were extensively characterized using X-ray diffraction, solid-state 27Al nuclear magnetic resonance spectroscopy, and thermogravimetric analysis with differential scanning calorimetry. A high-precision volumetric adsorption apparatus was used to characterize the surface area and to controllably dose ethanol onto the surface of the aluminas. A modified temperature programmed desorption (TPD) method which samples the molecular composition of the vapor at discrete temperatures in a closed cell is described. INS results were used to confirm adsorption of ethanol on γ- and θ-alumina and show the reaction of ethanol and subsequent formation of ethylene as a function of temperature. The TPD and INS results affirm that the dehydration reaction and subsequent formation of ethylene on both γ- and θ-aluminas occur rapidly at 300 °C, though ethanol is still observed on θ-alumina indicating fewer active sites. These results demonstrate the value of a multi-faceted characterization approach, featuring INS, towards providing a detailed understanding of the ethanol dehydration mechanism on θ-alumina and further provide the basis for extending this approach to other systems in heterogeneous catalysis and areas where molecule-substrate interactions are poorly understood.

La2CoO4+δ perovskite-mediated peroxymonosulfate activation for the efficient degradation of bisphenol A.

Sulfate radical-based technology has been considered as an efficient technology to remove pharmaceuticals and personal care products (PPCPs) with heterogeneous metal-mediated catalysts for the activation of peroxymonosulfate (PMS). In this study, La2CoO4+δ perovskite with Ruddlesden-Popper type structure was synthesised by the sol-gel method, which was employed in PMS activation. Different characteriazation technologies were applied for the characterization of La2CoO4+δ , such as SEM-EDX, XRD, and XPS technologies. A common organic compound, bisphenol A (BPA), is used as a target contaminant, and the effect impactors were fully investigated and explained. The results showed that when the dosage of La2CoO4+δ was 0.5 g L-1 and the concentration of PMS was 1.0 mM in neutral pH solution, about 91.1% degradation efficiency was achieved within 25 minutes. Quenching experiments were introduced in the system to verify the catalytic mechanism of PMS for the BPA degradation, proving the existence of superoxide, hydroxyl radicals and sulfate radicals, which are responsible for the catalytic degradation of BPA. Moreover, the reusability and stability of the catalyst were also conducted which showed good stability during the reaction. This work would improve the applications of A2BO4-type perovskites for activating PMS to degrade BPA.

Revealing the interfacial water structure on a p-nitrobenzoic acid specifically adsorbed Au(111) surface.

The detailed structure of the water layer in the inner Helmholtz plane of a solid/aqueous solution interface is closely related to the electrochemical and catalytic performances of electrode materials. While the applied potential can have a great impact, specifically adsorbed species can also influence the interfacial water structure. With the specific adsorption of p-nitrobenzoic acid on the Au(111) surface, a protruding band above 3600 cm-1 appears in the electrochemical infrared spectra, indicating a distinct interfacial water structure as compared to that on bare metal surfaces, which displays a potential-dependent broad band in the range of 3400-3500 cm-1. Although three possible structures have been guessed for this protruding infrared band, the band assignment and interfacial water structure remain ambiguous in the past two decades. Herein, by combining surface-enhanced infrared absorption spectroscopy and our newly developed quantitative computational method for electrochemical infrared spectra, the protruding infrared band is clearly assigned to the surface-enhanced stretching mode of water molecules hydrogen-bonded to the adsorbed p-nitrobenzoate ions. Water molecules, meanwhile, are hydrogen-bonded with themselves to form chains of five-membered rings. Based on the reaction free energy diagram, we further demonstrate that both hydrogen-bonding interactions and coverages of specifically adsorbed p-nitrobenzoate play an important role in determining the structure of the water layer in the Au(111)/p-nitrobenzoic acid solution interface. Our work sheds light on structural studies of the inner Helmholtz plane under specific adsorptions, which advances the understanding of structure-property relationships in electrochemical and heterogeneous catalytic systems.