Surface Acidic Properties Research Articles

3D Interconnected Mesoporous Alumina with Loaded Hemoglobin as a Highly Active Electrochemical Biosensor for H2 O2.

Alumina is one of the most common and stable metal oxides in nature, which has been developed as a novel adsorbent in enrichment of biomolecules due to its excellent affinity to phosphor or amino groups. In this study, ordered mesoporous alumina (OMA) with interconnected mesopores and surface acidic property is synthesized through a solvent evaporation induced co-assembly process using poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer as a template and aluminium acetylacetonate (Al(acac)3 ) as the aluminium source. The pore size (12.1-19.7 nm), pore window size (3.5-9.0 nm) and surface acidity (0.092-0.165 mmol g-1 ) can be precisely adjusted. The highly porous structure endows the OMA materials with high hemoglobin (Hb) immobilization capacity (170 mg g-1 ). The obtained Hb@OMA composite is used as an electrocatalyst of biosensor for convienet and fast detection of hydrogen peroxide (H2 O2 ) with a low H2 O2 detection limit of 1.7 × 10-8 m and a wide linear range of 2.5 × 10-8 to 5.0 × 10-5 m. Moreover, the Hb@OMA sensors show a good performance in real time detection of H2 O2 released from Homo sapiens bone osteosarcoma, indicating their potential application in complex biological processes.

Controlled Hydrodeoxygenation of Phenolic Components in Pyrolysis Bio-oil to Arenes

Hydrodeoxygenation of phenolic components in pyrolysis bio-oil is considered to be a potential strategy for producing renewable aromatic chemicals. The key issue of this process is the establishment of an effective catalytic system that can cleave the CAr–O bonds without affecting the aromatic structure. To achieve this goal, an efficient heterogeneous catalyst with solid acid support (WOx/ZrO2) and active metal (Ru) was prepared in this study. The Ru–WOx/ZrO2 catalyst can effectively convert model phenolic compounds into aromatic hydrocarbons. For a mixed phenolic sample, the conversion to and selectivity for arenes were all around 90%. The good selectivity was proved to be strongly related to the surface adsorption and acid properties of the catalyst as well as the reaction pathway. Moreover, the hydrodeoxygenation of a pretreated bio-oil was also conducted and presented a satisfactory yield of arenes at 240 °C with 1 MPa of H2 reacted for 5 h. The depolymerization of high-molecular-weight phenolic olig...

Effect of V-containing precursors on the structure and catalytic performance of Cs-substituted phosphomolybdates for isobutane oxidation

A series of vanadium-substituted Cs salt of heteropoly compounds (HPC) from different vanadium-containing precursors were synthesized to investigate the preferable vanadyl species for oxidation of isobutane to methacrylic acid (MAA) under oxygen-poor conditions. The effects of various precursors on the structure were explored by XRD, FT-IR, Raman, UV–vis diffuse reflectance, XPS, H2-TPR, NH3-TPD and IR spectra of pyridine adsorption, and their structure-performance relationship was further studied. It was firstly found that the vanadium-containing precursors played a crucial role in the structure (location of vanadyl species), surface acidity and redox properties (ratio of surface V4+/V5+ and Mo5+/Mo6+ redox couples) for series of as-prepared HPCs catalysts. The catalyst derived from vanadyl sulfate led to vanadyl species into the secondary structure of Keggin-type HPC, which exhibited suitable surface V4+/V5+ and Mo5+/Mo6+ ratio and higher surface acidity, thereby improving the catalytic activity and selectivity to MAA for selective oxidation of isobutane under oxygen-poor conditions. These understandings would be beneficial for further study of HPCs and developing of highly efficient catalysts for isobutane oxidation.

Acidic effect of porous alumina as supports for Pt nanoparticle catalysts in n-hexane reforming

Catalytic activity and selectivity of n-hexane reforming are changed significantly by the surface acidic properties of the alumina support following halogen treatment.

Synthesis, Characterization and Catalytic Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Supported Y-Zeolite Catalysts

Vapour phase catalytic dehydration of glycerol to acrolein was studied over phosphotungstic acid (PTA) supported (with different loadings of PTA) on Y-zeolite catalysts. The active component PTA was varied between 10 and 40% w/w on the support Y-zeolite and was synthesized by the wet impregnation method. The physico-chemical characterization of the catalyst samples was investigated by X-ray diffraction (XRD), FT-IR, Raman and by the gas adsorption measurements. The XRD results showed that active component PTA is highly dispersed in an amorphous form at lower loadings of PTA and attained a crystalline state beyond 20 wt% of PTA. Both Raman and FT-IR spectra indicated that the Keggin ion structure of PTA was present in a highly dispersed state in the supported PTA/zeolite catalysts as compared to the bulk form of PTA. Temperature programmed desorption (TPD) of ammonia and FT-IR spectra of pyridine adsorption were used to determine the acidic properties of the PTA catalysts. The TPD of ammonia showed the presence of moderate acidity on the catalyst surface. The total acidity increased with raise in PTA loading up to 20 wt% and beyond this, it had decreased. The FT-IR results suggested the presence of Bronsted acidity. The Pore size increased with PTA loading until 20 wt%. Finally, the PTA/zeolite catalysts were tested for the gas phase dehydration of glycerol in a fixed-bed, micro-reactor in the temperature range between 250 and 300 °C. Among all the catalysts tested, PTA (20 wt%)/zeolite showed a total conversion of 100% glycerol and a selectivity of 79% for acrolein. These results are correlated with surface acidity, textural and structural properties of the PTA/zeolite catalysts. Glycerol dehydration products over Lewis and Bronsted acidic sites.

Mesoporous activated carbon fibers synthesized from denim fabric waste: Efficient adsorbents for removal of textile dye from aqueous solutions

Denim fabric waste was used as a carbon precursor, and chemically activated with phosphoric acid in the ratio of 1:1 (v:m) under a slow pyrolysis process to obtain activated carbon fibers (ACFs). The chemical and physical properties of the ACFs were investigated from the thermogravimetric analysis (TGA), N2 porosimetry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR), Boehm titration method, and point of zero charge (pHPZC). The obtained ACFs showed high yield (53%), BET surface area of 1582 m2 g−1, mesoporous features (average pore diameter of 3.60 nm), and surface acidic properties (pHPZC value of 2.13 and 1.13 mmol g−1 of acidic groups). The ACFs were applied in the removal of textile dye, Remazol Brilliant Blue R (RBBR), from aqueous solution. The adsorption isotherm and kinetic studies showed that adsorption of RBBR on the ACFs were better described by the pseudo-second order kinetic model and the Freundlich equilibrium model. The maximum adsorption capacity of the ACFS for RBBR was determined to be 292 mg g−1, which is higher than other adsorbent materials reported in the literature. The adsorption thermodynamic parameters indicated that adsorption process is spontaneous and exothermic.

Influence of the anodizing process variables on the acidic properties of anodic alumina films

Abstract In the present work, the effect of the different variables involved in the process of aluminum anodizing on the total surface acidity of the samples obtained was studied. Aluminum foils were treated by the electro-chemical process of anodic anodizing within the following variable ranges: concentration = 1.5-2.5 M; temperature = 303-323 K; voltage = 10-20 V; time = 30-90 min. The total acidity of the samples was characterized by two different methods: acid-base titration using Hammett indicators and potentiometric titration. The results showed that anodizing time, temperature and concentration were the main variables that determined the surface acid properties of the samples, and to a lesser extent voltage. Acidity increased with increasing concentration of the electrolytic bath, whereas the rest of the variables had the opposite effect. The results obtained provide a novel tool for variable selection in order to use synthetized materials as catalytic supports, adding to previous research based on the morphology of alumina layers.

Molybdenum-containing systems based on natural kaolinite as catalysts for selective oxidation of aromatic sulfides

A natural kaolinite from Argentinean deposits, converted into metakaolin by thermal treatment at 823K and chemically modified, was used as a support for catalysts containing iso- and heteropolyanions (POMs and HPOMs) such as ammonium heptamolybdate (AHM) and ammonium Anderson phases [XMo6O24H6]3− [X(III)=Al, Co]. The catalytic performances were analyzed in the clean selective oxidation of diphenyl sulfide (DPS) with H2O2. The chemical modification included treatment in acid solution and functionalization with 3-(aminopropyl)trimethoxysilane (F). The characterization was carried out by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), FTIR and Raman spectroscopies. Textural properties were determined by N2 adsorption-desorption isotherms (BET method); surface acid properties (Brønsted and Lewis surface acid sites) were measured by FTIR of adsorbed pyridine.A noticeable increase of surface areas and chemical composition change of the support occurred by acid treatment. Functionalization with amino-siliceous agents yielded an appropriate surface for the adsorption of POMs and HPOMs. The system containing Mo presented conversions of diphenyl sulfide of around 90% and high selectivity to diphenyl sulfone near 95%.

Relationship between surface property and catalytic application of amorphous NiP/Hβ catalyst for n-hexane isomerization

The amorphous NiP nanoparticles were synthesized and a novel amorphous NiP/Hβ catalyst was prepared successfully further. Due to the superior surface property of amorphous NiP/Hβ catalyst, it exhibited good catalytic application for n-hexane isomerization. The catalytic activity of amorphous NiP/Hβ catalyst was close to that of the prepared Pt/Hβ sample, and better than that of commercial catalyst and crystalline Ni2P/Hβ catalyst. What's more, the amorphous NiP/Hβ catalyst shows high resistance to different sulfur compounds and water on account of its unique surface property.The effect of loading amounts on surface property and catalytic performance was investigated, and the structure-function relationship among them was studied ulteriorly. The results demonstrate that loading amounts have effect on textural property and surface acid property, which further affect the catalytic performance. The 10wt.% NiP/Hβ sample has appropriate pore structure and acid property with uniformly dispersed NiP nanoparticles on surface, which is helpful for providing suitable synergistic effect. The effects of reaction conditions on surface reactions and the mechanism for n-hexane isomerization were investigated further. Based on these results, the amorphous NiP/Hβ catalyst with superior surface property probably pavesa way to overcome the drawbacks of traditional noble metal catalyst, which shows good catalytic application prospects.

Water effects on the acidic property of typical solid acid catalysts by 3,3-dimethylbut-1-ene isomerization and 2-propanol dehydration reactions

Two model reactions, namely the Brønsted-acidity-specific skeletal isomerization of 3,3-dimethylbut-1-ene for evaluating the Brønsted acidity and dehydration of 2-propanol for the overall acidity at the catalyst surface, were employed in this work to measure the effect of water on the surface acidic property of typical solid catalysts (HZSM-5, γ-Al2O3 and Nb2O5). For the isomerization reaction, water addition in the reaction feed produced little effect on the catalysis of HZSM-5 but significantly positive effect on the catalysis of Nb2O5; the typical Lewis acidic γ-Al2O3 showed no activity for this reaction in either the presence or absence of water. For the dehydration reaction, the effect of water was generally negative on the catalysis of every catalyst, demonstrating that water presence resulted in poisoning more or less of the Lewis acidity on the catalyst surface. Water poisoning of the Lewis acidity on Nb2O5 also resulted in generation of Brønsted acidity and the higher the H2O partial pressure (or H2O-to-substrate ratio) the higher the newly generated Brønsted acidity. However, generation of Brønsted acidity did not happen on γ-Al2O3 and HZSM-5, regardless of the H2O partial pressure. Three Nb2O5 samples with varying calcination temperature were involved, and their behavior clearly indicated that the water effects on Nb2O5 also depended sensitively on the sample calcination temperature. Moreover, water presence increased the activation energy and selectivity for di-isopropyl ether of the dehydration reaction over γ-Al2O3 and Nb2O5, and thus affected the acidity distribution at the catalyst surface during the reaction.

Effect of aging temperature during refluxing on the textural and surface acidic properties of zirconia catalysts

Abstract Hydrous zirconia was synthesized via precipitation method, and effect of aging temperature during refluxing (30–100 °C) precursor solution was investigated. We found that the aging temperature influenced on structural and textural properties of the hydrous zirconia, with variations in the textural properties leading to changes in the surface properties of calcined zirconia, including the acid functionalities. In addition, ZrO2 aged at 100 °C exhibited the highest specific surface area and the highest Lewis and Bronsted acidities among the samples. Finally, enhanced catalytic activity was also observed for the ZrO2 samples prepared at higher aging temperatures in the dehydration of iso-propanol.

Investigation on the cleavage of β-O-4 linkage in dimeric lignin model compound over nickel catalysts supported on ZnO-Al2O3 composite oxides with varying Zn/Al ratios

Catalytic depolymerization of lignin is still a challenge due to its low conversion and repolymerization of the reactive intermediates. Reductive depolymerization over supported nickel catalysts with probable surface acidic and basic properties is a very promising process. It is therefore very important to investigate the effect of acidity and basicity of the supports on catalytic reactivity. In this paper, we synthesized a series of nickel based catalysts supported on ZnO-Al2O3 composites with varying Zn/Al atom ratios (Zn/Al=2, 3, 5, ∞) and tested their catalytic performances over a model compound 2-phenoxy-1-phenylethanone containing β-O-4 bond. All these catalysts showed 100% conversion by reacting at 250°C for 2h under 2MPa of H2. Higher selectivity towards ethylcyclohexane could be obtained over the catalyst Ni/ZnO-Al2O3-5. The possible cleavage pathways of selective oxidized β-O-4 ether linkage have been proposed.

A novel solid acid coating catalyst on Q235 carbon steel for Fenton-like oxidation of phenol under circumneutral pH

Novel amorphous Fe3O4/FePO4/ZrO2 ceramic coatings as solid acid with porous structure were successfully synthesized in the phosphate electrolyte containing K2ZrF6 via plasma electrolytic oxidation (PEO) technique and characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The surface acidic property was investigated by NH3-TPD method. The results showed that the pore size and the intensity of pore interconnection of amorphous Fe3O4/FePO4/ZrO2 ceramic coating with solid acid property, increased with the increase of the K2ZrF6 dosage from 0.5 g to 2.0 g in the phosphate electrolyte. The Fenton-like performance of PEO coating catalysts was investigated by degradation of phenol under circumneutral pH. It was found that phenol removal efficiency decreased with the adding of K2ZrF6 amount from 0.5 g to 2.0 g except no catalytic activity of coating prepared without K2ZrF6, and Fenton-like PEO coating catalyst prepared with 0.5 g K2ZrF6 exhibited a superior catalytic activity which could degrade phenol thoroughly within 2 min under circumneutral pH. The strong acid sites played a dominant role in enhancing the Fenton-like catalytic activity. The excellent catalytic activity of PEO coating prepared in the phosphate electrolyte containing K2ZrF6 endowed it potential application in wastewater treatment.

Design of a novel immobilized solid acid coating and its application in Fenton-like oxidation of phenol

A novel immobilized solid acid coating on Q235 carbon steel was successfully prepared via plasma electrolytic oxidation. Sulfate functionalized Fe3O4/FeAl2O4 was confirmed by XRD, TEM and XPS analysis and surface acidic property was verified by NH3-TPD measurement. Fenton-like degradation performance was evaluated by employing phenol as target pollutant. Fast phenol degradation under the wide range of pH (pH 6–9) was accomplished within only 11min. Without sulfate functionalization, phenol could hardly be degraded by Fenton-like oxidation which meant that after sulfate functionalization the existence of acidic microenvironment on the catalyst surface not only provided an optimal circumstance for enhanced Fenton-like reaction, but also avoided adjusting pH of the treated wastewater. A reasonable Fenton-like degradation mechanism was proposed. This paper offered a novel design thought for synthesizing excellent Fenton-like coating catalyst under circumneutral pH.

High performance of H3BO3 modified USY and equilibrium catalyst with tailored acid sites in catalytic cracking

Increasing the cracking ability of catalyst by adjusting its surface acid property is of great significance for oil refining industry. The effects of boric acid on the structure and surface acidity of ultra stabilized Y (USY) and FCC equilibrium catalyst during the modification were investigated. The structural and surface properties of the prepared samples were characterized by low-temperature N2 sorption, XRD, 27Al and 29Si MAS NMR, and FTIR using pyridine probe molecule. Modified USY and equilibrium catalyst possessed reduced Lewis acid sites. The Brönsted/Lewis acid ratios of USY increased from 0.64 to 1.56 after modification, at the same time, the microporous surface areas increased, due to the nonframework and framework dealumination during the modification. The catalytic cracking tests were performed on a bench-scale micro reactor at 500 °C and atmospheric pressure, using n-dodecane as a modeling reactant and vacuum gas oil as conventional feedstock. The results showed that modified samples with high Brönsted acid sites had better cracking abilities and increased hydrogen transfer activity than raw samples.

Ultra-low loading of copper modified TiO2/CeO2 catalysts for low-temperature selective catalytic reduction of NO by NH3

A series of ultra-low content copper-modified TiO2/CeO2 catalysts were prepared by wet impregnation method and tested for selective catalytic reduction of NO by NH3. The catalyst with a Cu/Ce molar ratio of 0.005 showed the best low-temperature activity and excellent sulfur-poisoning resistance. It was worth noting that the very small amounts of copper addition can lead to three times the activity at low temperature. The prepared catalysts were characterized by XRD, BET, Raman, XPS, NH3-TPD and the results revealed that the introduction of copper increased the amount of surface adsorbed oxygen and Ce3+ species on the catalyst surface and generated more Brønsted acid sites. The redox and surface acidic properties were also improved by the addition of Cu. All these factors played important roles in enhancing NH3-SCR performance of TiO2-CuO/CeO2 catalysts. Furthermore, in situ DRIFT experiments demonstrated that Cu doping enhanced the adsorption capacity of NH3 while the appearance of CuO weakened the adsorption ability of bridging nitrates, both the two factors synergistically facilitated the NH3-SCR reaction proceed smoothly via the Eley-Rideal pathway.

Synthesis of ordered porous zirconia containing sulfate ions and evaluation of its surface acidic properties

The synthesis and characterization of sulfated ZrO2 with ordered pores as a solid acid catalyst were investigated. Ordered porous ZrO2 containing sulfate ions was synthesized by hydrolysis of zirconium n-propoxide in the presence of HCl, surfactant and (NH4)2SO4 dissolved in distilled water, when the SO4/Zr molar ratio was changed in the range of 0.8–1.4. BET surface area of sulfated ZrO2 thus synthesized was found to be 150–160 m2 g−1. The presence of sulfate ions in ZrO2 was confirmed by an appearance of IR band at ca. 1398 cm−1 in the IR spectra of sulfated ZrO2. Since two IR bands due to surface hydroxyl groups were still observed for sulfated ZrO2, the possibility that sulfate ions are highly dispersed on the surface of ordered porous ZrO2 was suggested. From the evaluation of surface acidity by NH3-TPD measurements, not only the amount of NH3 desorption but also the strength of acid sites related to NH3 desorption temperature were found to be increased with increasing the SO4/Zr ratio up to 1.2. On the other hand, FTIR spectroscopy following pyridine adsorption revealed that the maximum surface density of Bronsted acid sites was attained for sulfated ZrO2 with SO4/Zr ratio of 1.0. Sulfate species interacting strongly with nano-sized tetragonal ZrO2 was considered to be responsible for the creation of Bronsted acid sites. In accordance with the surface density of Bronsted acid sites, sulfated ZrO2 with SO4/Zr ratio of 1.0 showed the highest activity for the skeletal isomerization of 3,3-dimethylbut-1-ene, which predominantly occurs on Bronsted acid sites.

Improvement in activity and alkali resistance of a novel V-Ce(SO4)2/Ti catalyst for selective catalytic reduction of NO with NH3

A series of V-Ce(SO4)2/Ti catalysts for selective catalytic reduction (SCR) of NO with ammonia are prepared by impregnation method. Low temperature SCR activity and alkali resistance of the optimal V-0.5Ce(SO4)2/Ti sample are found to be better than on the commercial V-W/Ti catalyst. Also, V-0.5Ce(SO4)2/Ti shows an excellent durability in the presence of SO2 and H2O, indicating to have prospects for the industrial application.Based on catalysts characterization and in-situ DRIFTS studies, a higher proportion of surface active oxygen generated by the introduction of Ce and a much faster H2 reduction point out the improved redox properties of V-0.5Ce(SO4)2/Ti, which results in a stronger NO oxidative activation and is confirmed by a more abundant formation of surface NO+ and NO3− species. When exposed to SCR conditions where both NH3 and NO are present, this enhanced NO activation can produce more reactive nitrite and/or NO+ intermediates which then readily react with adsorbed NH3 and decompose to N2 and H2O, accounting for the improved SCR activity of V-0.5Ce(SO4)2/Ti at low temperatures.The addition of Ce(SO4)2 also provides abundant reactive acid sites and adsorbed NH3 species thus increase. Even after Na poisoning, adequate surface acidity and redox properties still remain. Furthermore, relatively higher contents of V-OH are preserved owing to the interaction between Na and OSO, acting as a protection for the active sites. These promotional effects contribute to the better alkali resistance of V-0.5Ce(SO4)2/Ti. Therefore, all the results suggest that V-0.5Ce(SO4)2/Ti is a promising candidate as a catalyst for NH3-SCR in coal-fired power plants, especially under high Na-content conditions.

Promotion of catalytic performance by adding W into Pt/ZrO2 catalyst for selective catalytic oxidation of ammonia

Pt-WO3/ZrO2 catalyst was prepared by co-impregnation method to improve the ammonia oxidation performance of Pt/ZrO2. Differences in textural, structural, surface chemical states, redox properties and acid properties, together with the catalytic performance of Pt/ZrO2 and Pt-WO3/ZrO2 catalysts were investigated systematically. The results of H2-TPR revealed that higher reduction ability was possessed by Pt-WO3/ZrO2 than that of Pt/ZrO2 due to the influence of tungsten on platinum. The XPS results showed that electron transfer from tungsten to platinum species made higher electron density around platinum. The TEM results revealed that the active lattice plane Pt[111] was obtained by modification of W species. Consequently, Pt-WO3/ZrO2 exhibited obviously better ammonia oxidation performance compared with Pt/ZrO2, the light-off temperature of NH3 shifted from 284°C to 249°C, the activation energy decreased from 113.4 kJmol−1 to 96.2 kJmol−1.

Mechanism-dependent on the different CeO 2 supports of phosphotungstic acid modification CeO 2 catalysts for the selective catalytic reduction of NO with NH 3

Abstract The mechanism of phosphotungstic acid modification CeO 2 catalysts (P-W/CeO 2 ) with different CeO 2 supports were investigated by in situ diffuse reflectance infrared transform spectroscopy for the selective catalytic reduction of NO by NH 3 . The results indicated that the NH 3 -SCR reaction over P-W/CeO 2 followed both the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism. The reaction between NH 4 + and bidentate nitrate (NO 3 − ) took place, and then the H 2 O, N 2 and adsorbed NO 2 were formed. The coordinated NH 3 species reacted with adsorbed NO 2 and gaseous NO to generate N 2 and H 2 O. The interaction between CeO 2 and phosphotungstic acid contributed to the favored surface acidity (Lewis and Bronsted acid sites) and excellent redox property. The Bronsted acid sites facilitated the generation of NO 2 -adsorbed and Lewis acid sites accelerated the Eley–Rideal mechanism, while the NO oxidation to bidentate nitrate or NO 2 -adsorbed species was an important step in the reaction mechanism of P-W/CeO 2 .