Strong Electrostatic Adsorption Research Articles

Arginine-Functional Methacrylic Block Copolymer Nanoparticles: Synthesis, Characterization, and Adsorption onto a Model Planar Substrate.

Recently, we reported the synthesis of a hydrophilic aldehyde-functional methacrylic polymer (Angew. Chem., 2021, 60, 12032-12037). Herein we demonstrate that such polymers can be reacted with arginine in aqueous solution to produce arginine-functional methacrylic polymers without recourse to protecting group chemistry. Careful control of the solution pH is essential to ensure regioselective imine bond formation; subsequent reductive amination leads to a hydrolytically stable amide linkage. This new protocol was used to prepare a series of arginine-functionalized diblock copolymer nanoparticles of varying size via polymerization-induced self-assembly in aqueous media. Adsorption of these cationic nanoparticles onto silica was monitored using a quartz crystal microbalance. Strong electrostatic adsorption occurred at pH 7 (Γ = 14.7 mg m-2), whereas much weaker adsorption occurred at pH 3 (Γ = 1.9 mg m-2). These findings were corroborated by electron microscopy, which indicated a surface coverage of 42% at pH 7 but only 5% at pH 3.

An interplay between Ni and Brønsted and Lewis acid sites in the hydrodesulfurization of dibenzothiophene.

NiMo-S₂/γ-Al₂O₃ catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS₂ promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by the Strong Electrostatic Adsorption (SEA) method over four supports with different types of acidity: silica (~ neutral acidity), γ-Al₂O₃ (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

Insight into adsorption properties and mechanism of geopolymer adsorbents with inherent alkali release for tetracycline

The crux to practical application of geopolymer adsorbents for antibiotics that are easily protonated and deprotonated is to clarify the dynamic adsorption mechanism of geopolymer with intrinsic alkaline release. The adsorption properties, adsorption mechanism, adsorption-desorption cycle and waste adsorbent regeneration based on the geopolymer adsorbent for adsorbing tetracycline under the spontaneous dynamic pH conditions were systematically investigated by experiment, characterization and density functional theory. The results confirmed that the structures of tetracycline depended on dynamic pHs of adsorption systems changed by geopolymer adsorbent. The electrostatic interaction assisted by hydrogen-bonding and n-π interaction dominated the adsorption process when the dynamic pHs were less than 7. And the hydrogen-bonding and n-π interaction provided the possibility of weak adsorption effect in highly alkaline environments. The geopolymer powder exhibited outstanding adsorption efficiency (∼95.62%, 30 min) due to the strong electrostatic adsorption between electronegative skeleton of geopolymer and zwitterions species tetracycline under dynamic pH range of 4–6.3 and fitted the pseudo-second-order model. The outstanding competitive adsorption properties in NaCl solution, adsorption (4 times)-desorption (3 times) cycle properties and regenerative property of waste adsorbent were exhibited. The mechanism study based on the dynamic pHs which is closer to actual conditions can provide important reference for practical application of easy preparation and low cost geopolymer adsorbents.

Boosting the selective hydrogenation of biphenyl to cyclohexylbenzene over bimetallic Ni-Ru/SiO2 catalyst via enhancing strong metal-support interaction

Tuning the metal-support interaction (MSI) between highly dispersed nanosized metal particles and the support plays a pivotal role in the activity and selectivity of polyaromatics selective hydrogenation. In this work, the supported bimetallic Ni-Ru/SiO2-SEA catalyst was prepared by a strong electrostatic adsorption (SEA) strategy, and applied for the selective hydrogenation of biphenyl (BP) to cyclohexylbenzene (CHB). Compared to the catalysts prepared by the conventional incipient wetness impregnation method and Ni/SiO2-SEA, the significant effects of MSI and hydrogen spillover on Ni-Ru/SiO2-SEA facilitated the highly exposed and uniformly dispersed electron-deficient Niδ+ (0 < δ < 2) species, which could enhance adsorption and activation of the electron-withdrawing phenyl group and H2, thereby promoting the efficient and selective conversion of BP to CHB. At the conditions of 160 ℃ and 2 MPa H2 pressure, BP conversion over Ni-Ru/SiO2-SEA reached nearly 100 % within 3 h, achieving a remarkable selectivity of 97.9 % towards CHB, along with a high turnover frequency of 2756.9 h−1 for the active metallic Ni sites. Importantly, according to the kinetic simulations, the hydrogenation rate constant of Ni-Ru/SiO2-SEA was the highest (2.76 × 10-2 mol·g−1·h−1) among the employed catalysts. Moreover, after six consecutive cycles, no obvious decline in hydrogenation efficiency was observed, confirming the remarkable activity and stability of Ni-Ru/SiO2-SEA. Furthermore, the activation of BP and desorption of CHB pathway on the Niδ+ species were elaborated through temperature-programmed desorption characterization, highlighting the prominent contribution of MSI in enhancing the selective hydrogenation of polyaromatics.

Ultrasonic in-situ reduction preparation of SBA-15 loaded ultrafine RuCo alloy catalysts for efficient hydrogen storage of various LOHCs

SBA-15-loaded RuCo alloy nanoparticle catalysts (RuxCoy/S15-SU) for the efficient catalysis of hydrogen storage by various liquid organic hydrogen carriers (LOHCs) were prepared via strong electrostatic adsorption (SEA)-ultrasonic in-situ reduction (UR) technology. The above prepared catalysts were subjected to a series of characterization, such as XPS, H2-TPD/TPR, N2 adsorption–desorption, ICP, CO-chemisorption, FT-IR, XRD and TEM. Ru3+ and Co2+ were evenly anchored on the surface of SBA-15 by SEA, and ultrafine RuCo alloy nanoparticles were formed by UR without any chemical reducing or stabilizing agents. The addition of Co enhanced the dispersion and antioxidant capacity of the RuCo alloy NPs with an average particle size of 2.07 nm and increased the number of catalytically active sites. The synergistic effect of ultrafine particle size and electron transfer between Co and Ru improved the catalytic performance of monobenzyltoluene (MBT) for hydrogen storage. SEA-UR technology strengthened the coordination effect between RuCo alloy NPs and Si-OH, which enhanced the catalytic stability. H2-TPD and H2-TPR indicated that the addition of Co led to more activated H2 to produce hydrogen overflow. For the hydrogenation of MBT, the produced Ru2Co1/S15-SU showed excellent catalytic performance. The hydrogen storage efficiency of MBT was 99.98 % under 110 °C and 6 MPa H2 for 26 min, and the TOF was 145 min−1, which is significantly superior to that of Ru/S15-SU catalyst and that reported in the literature. The hydrogen storage efficiency was still as high as 99.7 % after ten cycles, which was much better than that of Ru/S15-SU and commercial 5 wt% Ru/Al2O3. Ru2Co1/S15-SU is also suitable for efficiently catalyzing hydrogen storage of N-ethylcarbazole, dibenzyltoluene and acenaphthene.

PtZn/ZnO intermetallic catalyst prepared by reactive metal-support interaction for the semi-hydrogenation of 1,4-butynediol

The continuous flow selective hydrogenation of 1,4-butynediol to 2-butene-1,4-diol places high demands on the activity and stability of the catalyst. Herein, an intermetallic PtZn/ZnO catalyst is designed by using the coupling strategy of strong electrostatic adsorption and subsequent reactive metal-support interaction. The TOF value of the Pt/ZnO-H500 catalyst, including PtZn intermetallic compound with electron-rich Ptδ- active sites, reaches 1421.6 h−1, which is almost 8 times higher than that of Pt/ZnO-H200 catalyst with monometallic Pt as active sites. The activation energy of Pt/ZnO-H500 catalyst (35.5 kJ mol−1) is significantly lower than that of Pt/ZnO-H200 catalyst with 49.9 kJ mol−1. In addition, the Pt/ZnO-H500 presents high stability in the continuous flow selective hydrogenation of 1,4-butynediol to 2-butene-1,4-diol for 75 h. These results suggest the intermetallic PtZn/ZnO presents as an alternative Pt-based catalyst without modification by toxic metals or organic matter and is a promising catalyst for directional hydrogenation in fine chemical synthesis.

The Effect of Reduction Pretreatments on the Size of Supported Pt and Pd Nanoparticles Prepared by Strong Electrostatic Adsorption

AbstractSupported catalyst synthesis involves pretreatment (drying, reduction) of metal complexes to form metal nanoparticles. This study has been undertaken to explore the effect of reduction temperature, heating rate, and water partial pressure on final particle size of Pt and Pd supported on a total of four carbon and oxide supports. Supported nanoparticles were synthesized by strong electrostatic adsorption (SEA) and dry impregnation (DI); the former method was hypothesized to yield greater nanoparticle stability in thermochemical reducing environments stemming from the strong interaction of the precursor with the support during impregnation. Reduced samples were characterized by in-situ and ex-situ XRD and STEM. The DI-derived samples generally showed an expected increase of particle size with increased reduction temperature, and severe particle coalescence in humid hydrogen, while the SEA-derived samples did not sinter at the elevated reduction temperatures (up to 500 °C) and were remarkably stable in the humid reducing environment. Graphical Abstract

Surface immobilization mechanisms of cobalt ions on hydroxyapatite catalyst supports

Cobalt deposition in an excess of solution was used to design Co-modified hydroxyapatite materials with various Co loadings and controlled dispersion. It is rationalized how the properties of hydroxyapatite supports (more or less stoichiometric compositions, nanorod or platelet morphologies and crystalline (100) zig-zag termination or non-apatitic hydrated external layer), influence the immobilization processes of Co by operating either with slightly acidic (natural) or basic pH of the suspension media. Four cobalt immobilization mechanisms impacting the final dispersion of Co on hydroxyapatites were identified by combining structural (XRD, 1H and 31P solid-state NMR, UV-Vis, Raman and X-ray fluorescence spectroscopies), surface (XPS) characterizations of Co-modified hydroxyapatites after drying and thermal treatment at 500 °C, and monitoring of the pH and the composition of the supernatant solutions during the Co deposition step. On dried Co-modified crystalline stoichiometric hydroxyapatite nanorods, cobalt is highly dispersed through cationic exchange or strong electrostatic adsorption (SEA) at slightly acidic or basic pH, respectively. After thermal treatment at 500 °C, only cation exchange preserved atomic dispersion of Co(II) ions since Co3O4 nanoparticles were observed on samples for which Co deposition occurred via SEA. On defective hydroxyapatite platelets, cobalt deposited at acidic natural pH could diffuse in an external non-apatitic layer, whereas under basic pH media, this surface layer was hydrolysed, resulting in the formation of a cobalt-substituted hydroxyapatite layer in which only a limited fraction of the surface cobalt species could be probed by XPS.

Study on flocculation performance and mechanism of cationic polyacrylamide on montmorillonite: Insights from experiments and molecular simulations

To achieve efficient flocculation of fine montmorillonite particles, molecular simulation and flocculation test were investigated to explore the influence of cationic monomer on the performance of cationic polyacrylamide (CPAM) flocculating montmorillonite particles. Three cationic monomers including methylacryloxyethyl trimethyl ammonium chloride (DMC), acrylamide propyl trimethyl ammonium chloride (ATMAC), and methylacrylamide propyl trimethyl ammonium chloride (MAPTAC) were copolymerized with acrylamide (AM) to produce CPAM copolymers. The simulation results suggested the electrostatic interaction was the primary internal propelling force for the stable adsorption of three distinct CPAM copolymers on the montmorillonite/water interface, followed by hydrogen bonding. Flocculation test indicated that CPAM has better flocculation effect on fine montmorillonite particles only when it has strong electrostatic adsorption and bridging capacity. This research establishes a theoretical foundation for the structural design of new flocculants for fine clay minerals.

Anchoring highly dispersed metal nanoparticles by strong electrostatic adsorption (SEA) on a dealuminated beta zeolite for catalysis

Enhanced interaction between metal precursors and silanol nests was demonstrated on a silanol-rich dealuminated beta zeolite by strong electrostatic adsorption, leading to the formation of highly dispersed Ni nanoparticles for effective catalysis.

CO2 Reforming with Ethanol for Syngas Production over SiO2‐M@CeO2 Catalysts (M: Cu,Ni): Impact of Active Metal

AbstractIt is of great significance to design the high‐performance catalysts with good anti‐sintering and coke‐resistance properties which can efficiently convert undesirable greenhouse gas CO2 with bio‐ethanol into high value‐added syngas. To be addressed this issue, a series of SiO2‐M@CeO2 (M: Cu, Ni) catalysts with typical core@shell structure were prepared via a strong electrostatic adsorption technique. Interestingly, Ni‐based catalyst exhibited the higher activity towards ethanol dry reforming at the relatively low temperature. Meanwhile, SiO2‐Ni@CeO2 catalyst presented good stability after a 50 h tests while a serious deactivation occurred for SiO2‐Cu@CeO2 within 20 h reaction due to heavy carbon deposition and reactor blockage. Herein, the higher catalytic performance of SiO2‐Ni@CeO2 catalyst compared to SiO2‐Cu@CeO2 sample was attributed to the combination effect of its mesoporous structure, higher Ni dispersion as well as stronger Ni‐Ce interaction as depicted by BET, TEM, XPS, H2‐TPR and XRD findings. This work might provide meaningful information to other reforming processes involving coke formation and active metal sintering problems.

Preparation of SBA-15 supported Ru nanocatalysts by electrostatic adsorption-ultrasonic in situ reduction method and its catalytic performance for hydrogen storage of N-ethylcarbazole.

N-ethylcarbazole (NEC) is an ideal liquid organic hydrogen storage carrier. The development of efficient hydrogen storage catalysts can promote the large-scale application of this process. In this paper, SBA-15 supported Ru nanocatalysts (Ru/S15-SU) were synthesized by strong electrostatic adsorption (SEA)-ultrasonic in situ reduction method (UR). Ru/S15-SU was characterized by N2 adsorption-desorption, TEM, H2 temperature program reduction, FT-IR, XRD, and XPS analysis measures. The results showed that ultrafine Ru NPs were evenly distributed on the surface of SBA-15, and ultrasonic in situ reduction not only reduced Ru3+ to Ru0, but also produced a coordination effect between Ru and O, enhancing the interaction between Ru NPs and the carrier. Ru/S15-SU exhibited excellent catalytic performance in the hydrogenation reaction of NEC, and the hydrogen storage efficiency reached 99.31% at 130°C and 6 MPa H2 pressure, which is superior to that of commercial 5wt%Ru/Al2O3. The excellent catalytic hydrogenation performance can be attributed to the selective anchoring of ruthenium ions on the surface of SBA-15 via electrostatic adsorption, preventing the aggregation of Ru NPs and enhancing the interaction between SBA-15 and Ru NPs by ultrasonic in situ reduction. Ru/S15-SU had a lower NEC hydrogenation apparent activated energy (Ea) of 68.45 kJ/mol than 5wt%Ru/Al2O3 catalyst. This method provides a new approach for the green preparation of nanocatalysts without using any chemical reducing agents.

Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles.

Non-oxidative ethanol dehydrogenation is a renewable source of acetaldehyde and hydrogen. The reaction is often catalyzed by supported copper catalysts with high selectivity. The activity and long-term stability depend on many factors, including particle size, choice of support, doping, etc. Herein, we present four different synthetic pathways to prepare Cu/SiO2 catalysts (∼2.5 wt % Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometer clusters), dry impregnation (A̅ = 3.4 nm; σ = 0.9 nm and particles up to 32 nm), strong electrostatic adsorption (A̅ = 3.1 nm; σ = 0.6 nm), and solvothermal hot injection followed by Cu particle deposition (A̅ = 4.0 nm; σ = 0.8 nm). All materials were characterized by ICP-OES, XPS, N2 physisorption, STEM-EDS, XRD, RFC N2O, and H2-TPR and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol-gel exhibited high Cu dispersion and, accordingly, the highest catalytic activity. Its acetaldehyde productivity (2.79 g g-1 h-1 at 255 °C) outperforms most of the Cu-based catalysts reported in the literature, but it lacks stability and tends to deactivate over time. On the other hand, the sample prepared by simple and cost-effective dry impregnation, despite having Cu particles of various sizes, was still highly active (2.42 g g-1 h-1 acetaldehyde at 255 °C). Importantly, it was the most stable sample out of the studied materials. The characterization of the spent catalyst confirmed its exceptional properties: it showed the lowest extent of both coking and particle sintering.

Reactive Deposition Versus Strong Electrostatic Adsorption (SEA): A Key to Highly Active Single Atom Co-Catalysts in Photocatalytic H2 Generation.

In recent years, the use of single atoms (SAs) has become of a rapidly increasing significance in photocatalytic H2 generation; here SAnoble metals (mainly Pt SAs) can act as highly effective co-catalysts. The classic strategy to decorate oxide semiconductor surfaces with maximally dispersed SAs relies on "strong electrostatic adsorption" (SEA) of suitable noble metal complexes. In the case of TiO2 - the classic benchmark photocatalyst - SEA calls for adsorption of cationic Pt complexes such as [(NH3 )4 Pt]2+ which then are thermally reacted to surface-bound SAs. While SEA is widely used in literature, in the present work it is shown by a direct comparison that reactive attachment based on the reductive anchoring of SAs, e.g., from hexachloroplatinic(IV) acid (H2 PtCl6 )leads directly to SAs in a configuration with a significantly higher specific activity than SAs deposited with SEA - and this at a significantly lower Pt loading and without any thermal post-deposition treatments. Overall, the work demonstrates that the reactive deposition strategy is superior to the classic SEA concept as it provides a direct electronically well-connected SA-anchoring and thus leads to highly active single-atom sites in photocatalysis.

Reaction pathways control of long-chain alkanes hydroisomerization and hydrocracking via tailoring the metal-acid sites intimacy

Designing a bifunctional catalyst to achieve efficient hydroisomerization of long-chain alkanes is very essential for producing high-performance fuel and lubricant base oils. Herein, a bifunctional catalyst composed of an intimate mixture of ZSM-48 zeolite and alumina binder and with platinum (Pt) metal controllably deposited on zeolite or alumina was fabricated by a strong electrostatic adsorption method. The dependence of reaction pathways of hydroisomerization and hydrocracking of n-hexadecane on the metal-acid sites intimacy was investigated. High Brønsted acid density and suitable metal-acid sites intimacy favored to promote the catalytic activity. The selectivity, hydroisomerization mechanism and hydrocracking mechanism were significantly altered by tailoring the metal-acid sites intimacy. Too large or too small metal-acid sites intimacy was conducive to inhibit the occurrence of pore-mouth mode. A linear decease of the hydroisomerization selectivity with the increase of acid steps (nas) was observed. The catalyst with nanoscale intimacy of metal-acid sites (Pt/A-48) showed the highest catalytic activity and isomer selectivity (87%) and the least acid steps (nas = 1.4). This work provides a promising approach to fabricating highly efficient and shape-selective bifunctional catalysts for selective hydroisomerization of long-chain alkanes. A reaction network was proposed over the catalysts with different metal-acid intimacy.

The role of MnOx in Cu-MnOx/SiO2 catalysts for the gas-phase hydrogenation of furfural

A series of Cu-MnOx/SiO2 catalysts was synthesized using different methodologies: incipient wetness impregnation and strong electrostatic adsorption for the incorporation of Cu species, and incipient wetness impregnation and controlled surface reactions for the addition of MnOx. The materials were characterized by H2-TPR, XRD, XPS, TEM/EDX, and N2 adsorption-desorption at -196 °C to study the interaction between Cu and MnOx species. These catalysts were evaluated in the gas-phase hydrogenation of furfural at 190 °C. While a highly dispersed Cu/SiO2 catalyst promoted the hydrogenolysis of furfuryl alcohol to methylfuran, it was found that the presence of oxygen vacancies in MnOx facilitated the interaction of the catalysts with the carbonyl group of furfural, thus promoting the formation of furfuryl alcohol as the main product.

High Efficiency Photocatalyst with Ultra‐Fine Pd NPs Constructed at Room Temperature for CO2 Reduction

AbstractThe photocatalytic CO2 converted into the value‐added products is regarded as a green strategy for the conversion and utilization of energy. Herein, we develop a commodious SEA (strong electrostatic adsorption) strategy to synthesize Pd‐based photocatalysts with ultra‐fine Pd NPs (Pd/TiO2−S−B). As verified by experiments and characterizations, the ultra‐fine Pd NPs can inexorably heighten the reaction activity of catalyst, because it can provide several functions consist of improving the carrier separation efficiency, light absorption and CO2 molecules adsorption. Meanwhile, the interaction of Pd and substrate can prevent the agglomeration of Pd NPs in reaction process. The designed Pd/TiO2−S−B contributes excellent performance in a gas‐solid system. The yields of CO (105.1 μmol/g‐cat) and CH4 (254.3 μmol/g‐cat) detected, are about 5.25 and 6.24‐fold higher than those of pristine TiO2. Pd/TiO2−S−B also exhibits the forceful stability with acceptable decline of catalytic activity after three cycles. This opens the door for the preparation of high‐performance and steady photocatalysts by reliable and effortless strategies toward CO2 reduction.

Enhanced Stability of Atomically Dispersed Pd Catalysts via Ionic Liquid Layer Deposition for Selective Acetylene Hydrogenation to Ethylene in Excess Ethylene

AbstractA series of TiO2‐supported Pd catalysts with different amounts of ionic liquid (IL) were synthesized for the selective hydrogenation of acetylene to ethylene in excess ethylene. CO Fourier transform infrared spectroscopy (FTIR), high‐angle annular dark‐field‐scanning transmission electron microscopy (HAADF‐STEM), and X‐ray photoelectron spectroscopy (XPS) suggested that the Pd species in the catalysts synthesized via the strong electrostatic adsorption (SEA) method exist predominantly as isolated atoms on TiO2 independent of the presence of the IL. Using a combination of FTIR and XPS, it was found that IL deposition on Pd catalysts induces a change in the electronic structure of atomically dispersed Pd atoms. The IL‐modified catalysts exhibited improved stability in acetylene hydrogenation compared to IL‐free catalysts owing to their higher coke resistance. Thus, this study provides a novel synthetic strategy based on IL deposition for improving the coke resistance and stability of atomically dispersed catalysts.

Contribution of surface carboxyl of cellulose in the formation mechanism and interfacial catalysis activity of ZnO/cellulose nanocomposites

The morphology, structure, and dispersion of photocatalysts play important roles in tailoring the surface active sites, photocatalytic productivity, and light utilization efficiency. Cellulose has been widely used in supporting and dispersing ZnO catalysts. However, surface groups of cellulose were ignored as a factor governing ZnO morphology. This work aims to explore the effects of cellulose surface groups on the formation and properties of ZnO catalysts. The reactivity, electronegativity, ion adsorption, and dispersion of the cellulose are improved after the introduction of carboxyl groups, which is beneficial to observe the induction of cellulose surface charge on the growth of ZnO. The results indicate that the diameter, sheet number, and thickness of flower-like ZnO in porous ZnO/cellulose nanocomposites are increased with the enhancement of cellulose surface electronegativity. The ZnO/cellulose nanocomposites with surface carboxyl content of 1.63 mmol*g−1 and zeta potential of –52.6 mV (ZnO/TOCNF3) have the highest photocatalytic activities and recycling for MO degradation due to the exposure of the interfacial active sites and strong electrostatic adsorption between carboxyl and ZnO. These findings provide a green method to regulate the formation and properties of catalysts by adjusting the surface electronegativity of cellulose nanofibers.

Supported silver and copper catalysts in the oxidative dehydrogenation of methanol to formaldehyde: a comparative study under industrially relevant conditions

Supported coinage-metal catalysts were prepared by strong electrostatic adsorption and used to assess the performance of silver and copper in the oxidative dehydrogenation of methanol to formaldehyde.