Effect Of Surface Hydroxyl Groups Research Articles

Modulating the Electronic Structures of Pt on Pt/TiO2 Catalyst for Boosting Toluene Oxidation.

Surface hydroxyl groups commonly exist on the catalyst and present a significant role in the catalytic reaction. Considering the lack of systematical researches on the effect of the surface hydroxyl group on reactant molecule activation, the PtOx/TiO2 and PtOx-y(OH)y/TiO2 catalysts were constructed and studied for a comprehensive understanding of the roles of the surface hydroxyl group in the oxidation of volatiles organic compounds. The PtOx/TiO2 formed by a simple treatment with nitric acid presented greatly enhanced activity for toluene oxidation in which the turnover frequency of toluene oxidation on PtOx/TiO2 was around 14 times as high as that on PtOx-y(OH)y/TiO2. Experimental and theoretical results indicated that adsorption/activation of toluene and reactivity of oxygen atom on the catalyst determined the toluene oxidation on the catalyst. The removal of surface hydroxyl groups on PtOx promoted strong electronic coupling of the Pt 5d orbital in PtOx and C 2p orbital in toluene, facilitating the electron transfers from toluene to PtOx and subsequently the adsorption/activation of toluene. Additionally, the weak Pt-O bond promoted the activation of surface lattice oxygen, accelerating the deep oxidation of activated toluene. This study clarifies the inhibiting effect of surface hydroxyl groups on PtOx in toluene oxidation, providing a further understanding of hydrocarbon oxidation.

Thioanisole oxidation promoted by new niobium-based catalyst: The effect of surface hydroxyl groups on catalytic performance

Thioanisole oxidation promoted by new niobium-based catalyst: The effect of surface hydroxyl groups on catalytic performance

AlPO4 film with transparent anti-fogging function imitating cicada wings

Glass surface fogging is a common problem in life. Here we provide a simple method to prepare an anti-fogging AlPO4 array that imitating cicada wings. The size of AlPO4 array can be adjusted by the concentration of the coating solution, the environmental humidity during the drying self-assembly process and the drying time. To explain the mechanism of morphology control, a model analysis was carried out based on surface tension, marangoni convection and a low temperature drying process. It is further realized the regulation of the hierarchical structure through the introduction of self-hygroscopic materials and a multi-step drying process based on the above theoretical model. The size of the array affects its performance. Nano AlPO4 array imitating cicada wing structure has great application value in the anti-fog field because of its high transparency, low haze, super-spreadability and wear resistance. The super-spreading anti-fog performance is achieved through the synergistic effect of surface hydroxyl groups, the bionanometer nanoarray structure and the internal pore structure.

Synergistic promotion effects of surface hydroxyl groups (-OH) and nitrate groups (-NO3) on catalytic ozonation of toluene over MnFe catalyst

A series of MnFe catalysts were prepared by hydrothermal synthesis combined with heat treatment at different temperatures. The characterizations demonstrated that MnFe-120 with both surface -OH and -NO3, MnFe-175 with surface -OH, MnFe-300 containing neither surface -OH nor -NO3, and MnFe-300-NO3 containing surface -NO3 were gained by drying or calcination and impregnation. The activity evaluation showed that the order of catalytic activity was MnFe-120 > MnFe-175 > MnFe-300-NO3 > MnFe-300. Further, characterizations and experiment results revealed that O3 adsorbed on the surface of the catalyst can interact with surface -OH and generated hydroxyl radicals (·OH). The presence of surface -NO3 provided more Lewis acid sites, thereby promoting H2O adsorption and conversion to the surface -OH, which supplemented the surface -OH consumed by the interaction with O3. It was deduced that the coexistence of surface -OH and -NO3 improved the production of·OH, which synergistically promoted the catalytic ozonation of toluene.

Competitive adsorption of asphaltene and n-heptane on quartz surfaces and its effect on crude oil transport through nanopores

• Competitive adsorption mechanism between asphaltene and n-heptane on quartz surfaces was illustrated from molecular perspective. • Influence of asphaltene deposition on the transport of light oil is clarified. • Work of adhesion and adsorption time ratio were proposed to quantify adsorption strength. • Flow behaviors of asphaltene and n-heptane in two quartz nanopores were compared. Asphaltene deposition is a ubiquitous problem in crude oil exploitation, which can cause the blockage of pore throat, leading to a significant reduction of oil recovery. Understanding the microscopic mechanism of asphaltene deposition and its influence on the oil flow in nanopores is critical for effective exploitation of crude oil. In this study, we investigated the competitive adsorption of asphaltene and n-heptane on quartz surfaces using molecular dynamics simulations. We found that asphaltene shows a much stronger adsorption ability on the quartz surfaces than n-heptane, resulting from both interfacial energy strength and the poly-aromatic ring interactions among asphaltene molecules. With the deposition of asphaltene, the flux of n-heptane transport in nanopores is greatly decreased, which can be attributed to the reduction of effective aperture size and the disappearance of possible slip near the surface. The difference in adsorption and flow behaviors between asphaltene and n-heptane can be further elucidated by the comparison in work of adhesion for several interfaces. Besides, the effect of surface hydroxyl groups of quartz substrates was proved to have a prominent impact on the adsorption of asphaltene on the quartz surfaces, leading to a considerable enhancement of oil flux through SiO 2 nanopores. Our work advances the understanding of the low oil recovery caused by asphaltene deposition and has a significant reference value to the effective production and evaluation of crude oil.

Ru/TiO2 catalyst for selective hydrogenation of benzene: Effect of surface hydroxyl groups and spillover hydrogen

Three Ru/TiO2 catalysts were prepared via an impregnation-chemical reduction method by supporting Ru on three different TiO2 supports, namely TiO2-A (anatase), TiO2-R (rutile) and TiO2-A-750 (annealing TiO2-A at 750 °C). The amount of surface hydroxyl groups in the TiO2 supports and Ru/TiO2 catalysts is evaluated by the FTIR technique, which is found to be affected by crystal and textural property of TiO2. It is found that, for the Ru/TiO2 catalyst, the presence of more spillover hydrogen, and more hydroxyl groups that lead to stronger surface hydrophilicity and lower benzene diffusion rate, thereby improve its catalytic activity and selectivity towards selective hydrogenation of benzene. For the Ru/TiO2-A catalyst, it has much more spillover hydrogen and hydroxyl groups than the other two, hence showing the best catalytic activity (TOF of 0.8 s−1) and cyclohexene selectivity (66%) at a benzene conversion of 50%.

Deciphering highly resistant characteristics to different pHs of oxygen vacancy-rich Fe2Co1-LDH/PS system for bisphenol A degradation

This first-attempt study explored interactive function of oxygen vacancies, transition metals, and surface hydroxyl groups for persulfate (PS) activation, at different pH conditions. Oxygen vacancy-rich Fe2Co1-LDHs was fabricated via calcination in hydrogen atmosphere. The Fe2Co1-LDH possessed the maximal concentration of oxygen vacancies and abundant hydroxyl groups for effective functioning according to the characterization through X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The BPA-degrading efficiency in the LDHs/PS system indicated that Fe2Co1-LDH exhibited the most promising activated performance since oxygen vacancies could improve the catalytic efficiency to enhance electron transport phenomena between the Fe and Co. N2 experiments proved that the presence of oxygen vacancies could promote the production of 1O2 and O2−. Phosphate and pH effect experiments showed the Fe2Co1-LDH/PS system stably maintained operation performance over a wide pH range for bisphenol A (BPA) removal with the effect of surface hydroxyl groups. Practical samples had little effect on the removal of BPA. According to the quenching experiments and EPR technology, SO4− was the main active radicals in acid and neutral conditions and apparently the OH played the crucial role at alkaline pHs. Two different major reaction routes at different pH levels in the Fe2Co1-LDH/PS system for mechanisms of BPA degradation were proposed herein. The Chemical intermediates of BPA degradation were identified by gas chromatography-mass spectrophotometry (GC–MS) analysis, and degradation pathways were proposed for system optimization.

The mechanism for promoted oxygenation of V(IV) by goethite: Positive effect of surface hydroxyl groups.

The most toxic and mobile form of vanadium (V) is V(V). Thus, the oxidation of V is a subject of considerable importance since the process may increase environmental risks of V. V(IV) is known to be stable when pH < 4.5. However, in this study, stable V(IV) was oxidized almost completely in goethite suspension within 60 min at pH 2.0 and pH 4.0, correspondingly, only 25%-30% and 15%-20% of V(IV) were oxidized in equimolar Fe3+ solution and the blank solution, respectively. The promoted oxidation of V(IV) by FeOOH is attributed to the formation of the complex, VO(OFe<)+ or VO(OFe<)2. On the one hand, the formation of the complex caused higher pH in the interface of solid FeOOH and corresponding lower conditional potential of V(V)/V(IV) than those in bulk solutions, which facilitates the oxidation of V(IV). On the other hand, the surface group OFe < may serve as a medium that facilitating the electron transfer from V(IV) ions to dissolved oxygen molecules, also favoring the oxidation of V(IV). This study not only deepens our understanding of the transfer, transformation, and risk of V in environments, but also provides a reference to speculate the fate of similar elements in environments.

Effects of surface hydroxyl groups induced by the co-precipitation temperature on the catalytic performance of direct synthesis of isobutanol from syngas

A series of Zn-Cr oxides catalysts with different content of surface hydroxyl groups were prepared at different co-precipitation temperature. These catalysts were used for direct synthesis of isobutanol from syngas with an aim to investigate the effect of co-precipitation temperature on the catalytic activity of Zn-Cr catalysts. The co-precipitation temperature had a strong influence on surface OH groups leading to the different activities of ZnCr catalysts. Catalysts characterizations by XPS, XRD, H2-TPR, CO2-TPD, in situ FTIR of CO absorption and DFT calculation clearly revealed that the surface OH groups played important role in the adsorption and activation of CO. The adsorption energy of CO is intensified by the presence of surface OH, and it is easier to form formats than carbonates owning to the low activation barrier and reaction energy. Therefore, selectivity for alcohols showed an increased tendency with increasing the surface OH content on catalysts. Among all ZnCr catalysts, catalyst prepared at 60 °C (ZC-60) showed the best catalytic performance due to the highest concentration of surface OH groups.

Effect of surface hydroxyl groups on heat capacity of mesoporous silica

This paper quantifies the effect of surface hydroxyl groups on the effective specific and volumetric heat capacities of mesoporous silica. To achieve a wide range of structural diversity, mesoporous silica samples were synthesized by various methods, including (i) polymer-templated nanoparticle-based powders, (ii) polymer-templated sol-gel powders, and (iii) ambigel silica samples dried by solvent exchange at room temperature. Their effective specific heat capacity, specific surface area, and porosity were measured using differential scanning calorimetry and low-temperature nitrogen adsorption-desorption measurements. The experimentally measured specific heat capacity was larger than the conventional weight-fraction-weighted specific heat capacity of the air and silica constituents. The difference was attributed to the presence of OH groups in the large internal surface area. A thermodynamic model was developed based on surface energy considerations to account for the effect of surface OH groups on the specific and volumetric heat capacity. The model predictions fell within the experimental uncertainty.

Molecular Dynamics Study on the Effect of Surface Hydroxyl Groups on Three-Phase Wettability in Oil-Water-Graphite Systems.

In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on the hydroxylated surfaces and obtain the relationship between water-oil-solid interfacial properties and the hydroxyl density, which results from the synthetic effects of the orientation of molecules and hydrogen bonds. With the increase of hydroxyl density, the water-solid contact angle first decreases rapidly, and then remains constant. The density of the hydrogen bond formed between hydroxyls and water molecules in the adsorption layer can explain the regularity of the three-phase wettability. The orientation of the water molecules in the adsorption layer shows insignificant variation, owing to the hydrogen bond network formed between the water molecules; thus, little change is observed in the hydrogen bond density in the adsorption layer.

Effect of surface hydroxyl groups on the dispersion of ceramic powders

The effect of surface hydroxyl groups (OH) on the dispersity of ceramic powders was explored using the common ceramic powder barium titanate (BaTiO3) as the study model. To simulate the presence of OH on the powder, which is generally formed because of atmospheric storage, oxidative hydroxylation with hydrogen peroxide was used to produce and adjust the concentration of surface OH. Owing to the presence of a lot of surface OH, BaTiO3 particles aggregated because of hydrogen bonding and required a large amount of dispersant such as the ammonium salt of poly(acrylic acid) (PAA-NH4) for its dispersion stabilization. In addition, the commonly used binder poly(vinyl alcohol) (PVA) became more competitive with PAA-NH4 for adsorption onto the hydroxylated BaTiO3, thereby reducing the efficiency of the dispersant and impeding the dispersion of the powder.

New insight into electrochemical-induced synthesis of NiAl2O4/Al2O3: Synergistic effect of surface hydroxyl groups and magnetism for enhanced adsorptivity of Pd(II)

A new promising adsorbent, Ni supported on γ-Al2O3 was prepared in a simple electrolysis system (Ni/Al2O3-E) in minutes and was compared with the sample prepared by a physical mixing method (Ni/Al2O3-PM). The adsorbents were characterized by XRD, TEM, FTIR, 27Al MAS NMR, XPS, and VSM. The results showed that besides NiO nanoparticles, a NiAl2O4 spinel was also formed in Ni/Al2O3-E during the electrolysis via the dealumination and isomorphous substitution of Ni2+ ions. In contrast, only agglomerated NiO was found in the Ni/Al2O3-PM. Adsorption test on removal of Pd2+ ions from aqueous solution showed that the Pd2+ ions were exchanged with the hydrogen atoms of the surface–OH groups of both adsorbents. Significantly, the Ni/Al2O3-E demonstrated a higher adsorption towards Pd2+ ions than Ni/Al2O3-PM due to its remarkably higher degree of magnetism, which came from the NiAl2O4. The use of 0.1gL−1 Ni/Al2O3-E gave the maximum monolayer adsorption capacity (qm) of 40.3mgg−1 at 303K and pH 5. The Ni/Al2O3-E showed high potential for simultaneous removal of various noble and transition metal ions and could be also used repetitively without affecting the high adsorptivity for Pd2+ ions. This work may provide promising adsorbents for recovery of various metals as well as other materials for such related applications.

CO2 Hydrogenation to Hydrocarbons over Iron-based Catalyst: Effects of Physicochemical Properties of Al2O3 Supports

The effects of surface hydroxyl groups and SiO2 content of alumina supports for FeK/Al2O3 catalysts on their activity and product selectivity for CO2 hydrogenation to hydrocarbons reaction were investigated. A series of iron-based catalysts supported on six commercial Al2O3 supports were prepared and tested for hydrocarbons production in a fixed-bed reactor. Surface acidic–basic hydroxyls distribution of the supports were evaluated by Fourier transform infrared (FT-IR) and point of zero charge (PZC) measurement. It was found that the PZC of Al2O3 supports strongly affects the dispersion as well as particle size of the Fe-based catalysts. Increasing PZC value of Al2O3, the iron dispersion increased and particle size decreased. The highest CO2 conversion (54.4%) and C5+ hydrocarbons selectivity (31.1%) were achieved when the PZC was 8.0. CO2 conversion and the long-chain products selectivity decreased when PZC declined. Moreover, SiO2-doping of alumina strongly affected the surface acidic–basic hydroxyls di...

A novel chromic oxide catalyst for NO oxidation at ambient temperature

Chromic oxide catalysts were prepared by ammonia precipitation method and first used in NO oxidation to NO2 at ambient temperature. After calcination at 300 °C, the catalyst exhibited higher catalytic activity with 100% conversion of NO and significantly longer lifetime than activated carbon or activated carbon fiber that has been reported so far. The effects of crystalline phases and surface hydroxyl groups on the activity as well as the durability of catalysts in NO oxidation were investigated by XRD, HRTEM, TG, XPS, Raman and DRIFT techniques. The results indicated that the amorphous structure and surface hydroxyl groups together contributed to the high catalytic activity and long-time stability of the catalysts. The promoting effect of surface hydroxyl groups for long-time stability was confirmed by the alkaline treatments of amorphous chromic oxide catalysts.

Catalytic Performance of Porous SiO&lt;sub&gt;2&lt;/sub&gt;&amp;middot;&lt;em&gt;x&lt;/em&gt;H&lt;sub&gt;2&lt;/sub&gt;O Supported RuB Nanoparticles for the Hydrogenation of Quinoline

A porous and hydroxyl group-rich catalyst RuB/SiO2·xH2O was prepared by hydrolyzing ethyl silicate,protecting SiO2·xH2O with polyvinyl pyrrolidone(PVP),and etching SiO2·xH2O with NaOH.The catalyst was characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),Fourier transform infrared(FT-IR) spectroscopy,and BET(Brunauer-Emmett-Teller).We found that the catalyst showed excellent performance for the hydrogenation of quinoline under mild condition.At a hydrogen pressure of 3.0 MPa and a reaction temperature of 80℃,the conversion of quinoline reached 95% and the selectivity for 1,2,3,4-tetrahydroquinoline was 97%.This porous catalyst also showed an excellent anti-poisoning characteristic.The catalyst can be reused several times.We also investigated the effect of surface hydroxyl groups and the solvent on catalytic activity and selectivity.The results showed that using water as a solvent leads to higher catalyst activity and selectivity for the hydrogenation of quinoline.The mechanism of quinoline hydrogenation over the catalyst is discussed.The coordination of the nitrogen on quinoline onto the surface of ruthenium nanoparticles,the effect of hydrogen bond among the surface hydroxyl groups of the catalyst and the nitrogen present in quinoline and in the water solvent were favorable for the adsorption of the substrate and the desorption of the products from the surface of the catalyst.

Hydrogenation of methyl propionate over Ru–Pt/AlOOH catalyst: Effect of surface hydroxyl groups on support and solvent

Abstract A ruthenium–platinum bimetallic catalyst supported on boehmite was prepared by co-impregnation and hydrothermal reduction and characterized by XRD, TEM and TG–DTG. Reduction time of the catalyst affected the conversion of γ-Al 2 O 3 to boehmite and the specific surface area of the catalyst, and consequently influenced the catalytic performance of the catalyst. Under the same conditions, the Ru–Pt/AlOOH catalyst showed much higher activity and selectivity than the Ru–Pt/γ-Al 2 O 3 in aqueous hydrogenation of methyl propionate. The selectivity to 1-propanol of 97.8% could be obtained at methyl propionate conversion of 89.1% over Ru–Pt/AlOOH at 453 K under 5 MPa of H 2 for 6 h. It is postulated that the high performance of this novel catalyst is related to the cooperation of the hydroxyl groups of support surface and water solvent.

Effect of surface hydroxyl groups of pure TiO2 and modified TiO2 on the photocatalytic oxidation of aqueous cyanide

It is still debatable whether the photocatalytic oxidation of cyanide proceeds via hydroxyl radicals or by photogenerated holes. We synthesized pure TiO2 catalysts via sol-gel process. In order to elucidate the oxidation pathway of cyanide, we used hydroxyl radical scavengers and controlled the concentration of surface hydroxyl group on the catalysts adopting fluoride-exchange. The degree of fluoride-exchange of TiO2 catalysts was independent of the pH of suspension. We also adopted a polyoxometalate, tungstophosphoric acid (TPA, H3PW12O40) which is well known for high charge transfer ability and hydrolytic stability. TPA-modified TiO2 catalysts were prepared with sol-gel technique to overcome the high solubility of TPA in water. As another attempt for the insoluble TPA, proton of TPA supported on TiO2 catalysts was replaced by cesium ion to form Cs-TPA/TiO2 catalysts. Both attempts were successful in immobilizing TPA on TiO2 catalysts. Commercially available TiO2 catalysts such as P25 from Degussa AG were also used as catalysts. XRD analysis revealed that pure TiO2 and TPA-modified TiO2 catalysts prepared by sol-gel process were composed of well-developed anatase crystalline structure. In the presence of hydroxyl radical scavengers, the photoactivity of TPA-modified TiO2 catalysts was retarded much less than that of pure TiO2 catalysts. The concentration of surface hydroxyl group was effectively suppressed by the fluoride-exchange causing the decrease of the activity of the catalysts. In the case of fluoride-exchanged catalysts, the drop in activity was obvious for the pure TiO2 catalysts in the presence of iodide as a hydroxyl radical scavenger suggesting that indirect oxidation via hydroxyl radicals was the preferential reaction pathway. For the TPA-modified TiO2 catalysts, meanwhile, the diminution was such a small extent suggesting that direct oxidation by photogenerated holes was the main reaction pathway. The activity arising from TPA in the catalysts was due to the Keggin structured anion (PW12O 40 3- ) which acted as an electron relay with the aid of dissolved oxygen in the reaction system.

Cu interactions with α-Al 2O 3(0001): effects of surface hydroxyl groups versus dehydroxylation by Ar-ion sputtering

X-ray photoelectron spectroscopy studies and first principles calculations compare Cu adsorption on heavily hydroxylated α-Al 2O 3(0001) with dehydroxylated surfaces produced by Ar + sputtering followed by annealing in O 2. Annealing a cleaned sapphire sample with an O 2 partial pressure of ∼5×10 −6 Torr removes most contaminants, but leaves a surface with ∼0.4 ML (ML: monolayer) carbon and ∼0.4 ML OH. Subsequent light (6 min) Ar-ion sputtering at 1 keV reduces the carbon to undetectable levels but does not dehydroxylate the surface. Further sputtering at higher Ar-ion excitation energies (>2 keV) partially dehydroxylates the surface, whereas 5 keV Ar-ion sputtering creates oxygen vacancies in the surface region. Further annealing in O 2 repairs the oxygen vacancies in the top layers, but those beneath the surface remain. Deposition of Cu on the hydroxylated surface at 300 K results in a maximum copper(I) coverage of ∼0.35 ML, in agreement with theoretical predictions. Maximum copper(I) coverage at 300 K decreases with decreasing surface hydroxylation. Exposure of a partially dehydroxylated sapphire(0001) surface to either 2 Torr H 2O vapor or air results in recovery of surface hydroxylation, which in turn increases the maximum copper(I) coverage. These results demonstrate that the hydroxyl surface coverage critically affects the ability of Cu to ‘wet’ sapphire(0001) at 300 K. In addition, first principles density functional calculations show that while an ad-OH species stabilizes copper(I) at room temperature, any nearby in-surface OH does the opposite.

Phase transition of capillary condensed liquids in porous silica: effect of surface hydroxyl groups

Phase transition temperatures of capillary condensed organic liquids in porous silica were measured using a 1020/DSC system (Perkin-Elmer Ltd.). The amounts and types of hydroxyl groups on the sample surfaces were precisely controlled to discuss the surface effect on the phase transition temperature. The melting point of the solid phase of benzene in the pores decreased with increasing concentration of the surface hydroxyl groups. On the other hand, in the case of n-hexane, such an effect was not observed. From these results, it is assumed that the liquid structure of capillary condensed benzene in the pores changes with the amounts and types of surface hydroxyl groups. This consideration is confirmed from IR spectroscopy.