Surface Lewis Acid Sites Research Articles

Catalytic ozonation of toxic pollutants over magnetic cobalt and manganese co-doped γ-Fe2O3

Magnetic Co- and Co, Mn-doped γ-Fe2O3 (FC and FCM) were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in situ attenuated total reflection FTIR (ATR-FTIR) spectroscopy and cyclic voltammetry (CV) analyses. FCM was found to be highly effective for the mineralization of 2,4-dichlorophenoxyacetic acid and its derivatives 2,4-diclorophenol, 2,4,6-trichlorophenol in aqueous solution with ozone. The characterization studies showed that Co and Mn incorporated in γ-Fe2O3 existed as multivalence oxidation states, and there were more Lewis acid sites on the surface of FCM. The interaction of ozone with chemisorbed H2O and surface hydroxyl groups generated from dissociative adsorption of H2O on Lewis acid sites initiated the production of reactive oxygen species. Moreover, a redox process was observed in the catalytic decomposition of O3 at the water–catalyst interface by CV analysis. The results indicated that the introduction of Mn not only increased the surface Lewis acid sites of FCM to cause more surface hydroxyl groups and chemisorbed water, but also enhanced the interfacial electron transfer, resulting in higher activity.

Speciation of Copper in Spherical Mesoporous Silicates: From the Microscale to Angstrom

MCM-41 type mesoporous silicate particles with spherical morphology containing copper nanospecies were synthesized by conventional hydrothermal synthesis. A narrow distribution of silicate particle sizes between 2 and 3 μm and a well-defined mesoporosity were evidenced by electronic microscopy, even for loadings of copper of about 10 wt %. Moreover, CuO nanoparticles ∼30 nm in diameter occluded in the amorphous silica, possibly filling some secondary mesoporosity, were also detected. By Fourier transform infrared spectroscopy with pyridine adsorption and UV−vis diffuse reflectance spectroscopy measurements together with reduction experiments under H2 flow, a detailed study about the relationship between copper loading degree and the acid properties with the local isolated Cuδ+ species surroundings was performed. The incorporation of copper into the silica framework generated surface Lewis acid sites which increase with copper content. The origin of these acid sites could be attributed to the presence of isolated Cuδ+ species possibly coordinated with the framework oxygen atoms. It is noteworthy that Brønsted acid sites were not detected in our materials. By X-ray absorption near edge structure spectroscopy, we determine the coexistence of copper +1 and +2 states. The average coordination numbers calculated from extended X-ray absorption fine structure experiments are consistent with a mixture of nanosized species of copper: CuO nanoparticles, besides isolated Cuδ+ cations located in framework positions with oligonuclear clusters like [Cuδ+···Oδ−···Cuδ+]n in its surroundings, confined within the pores.

Two-step biodiesel production from Jatropha curcas crude oil using SiO 2·HF solid catalyst for FFA esterification step

A high quality biodiesel was produced from Mexican Jatropha curcas crude oil (JCCO) by a two step catalyzed process. The free fatty acids (FFA) were first esterified with methanol, catalyzed by a solid catalyst: SiO 2 pretreated with HF. The catalyst showed a high number of Lewis acid surface sites, and no CO 2 or H 2O adsorption activity. This catalyst showed a high FFA esterification activity and high stability. After 30 esterification runs, the catalyst activity remained unchanged. During the second step, the triglycerides present in the JCCO were transesterified with methanol catalyzed by NaOH. The chromatographic analysis of the biodiesel obtained, revealed that the process proposed in this investigation led to a very high quality biodiesel, meeting the international requirements for its utilization as a fuel. The combustion gas emissions of the JCCO biodiesel were studied by FTIR spectroscopy using a laboratory combustor. These preliminary results showed low amounts of aromatic and sulfur containing compounds. However, halogenated compounds and dicyclopentadiene were also detected at the combustor exhaust.

Surface acidity and reactivity of β-FeOOH/Al2O3 for pharmaceuticals degradation with ozone: In situ ATR-FTIR studies

The surface acidity and reactive activity of β-FeOOH, mesoporous alumina (MA), β-FeOOH/MA were investigated in catalytic ozonation of pharmaceutically active compounds (PhACs) aqueous solution. β-FeOOH/MA showed high efficiency for the degradation and mineralization of ibuprofen and ciprofloxacin. Its surface Lewis acid sites on β-FeOOH/MA were more greatly enhanced compared with those on MA and β-FeOOH. In situ attenuated total reflection FTIR (ATR-FTIR) spectroscopy was used to investigate the interaction of D2O and O3 with the catalysts in aqueous phase under various conditions. The dissociative chemisorptions of D2O occurred at the surface Lewis acid sites of the catalyst. Furthermore, O3 interacted with the surface hydrogen-bonded –O–D and D2O to initiate reactive oxygen species (ROS). The stronger Lewis acid sites of β-FeOOH/MA caused the more chemisorbed water enhancing the interaction with ozone, resulting in higher catalytic reactivity. The observations verified that the Lewis acid sites were reactive centers for the catalytic ozonation of PhACs in water.

$CH_2CIF$ Adsorbed on $TiO_2$: Study of the Adsorbate-Substrate Interaction by IR Spectroscopy and DFT Calculations

Fourier-transform infrared spectroscopy has been used for the first time to study the adsorption of chlorofluoromethane (CH2ClF) on TiO2 at room temperature. The obtained spectra allow to deduce that the adsorbate-substrate interaction occurs through both the Cl and F atoms of the molecule and the surface Lewis acid site (Ti 4+ ) and by means H-bonds involving the CH2 group and the surface Lewis basic sites (O 2i or OH i ). In order to better comprehend these interactions, a periodic quantum- mechanical study at DFT/B3LYP level has been carried out by considering the anatase (101) surface and focusing the attention on the determination of the energetically pos- sible adsorbate-substrate structures. According to the comparison between the exper- imental and calculated vibrational frequencies, it can be concluded that the molecule can adsorb on the surface both through the Cl atom and an H-bond and by means the F atom and two H-bonds.

Advanced Drug Delivery Vectors with Tailored Surface Properties Made of Mesoporous Binary Oxides Submicronic Spheres

The synthesis of mesoporous silica-zirconia mixed oxides that can be used as efficient drug delivery carriers for bisphosphonates based drugs has been performed via spray-drying process. These silica-zirconia mixed oxides used for the first time as drug delivery systems exhibit mesostructures with tunable acidity. The two selected drugs were alendronate and zoledronate, which carry similar phosphonate heads but different amine tails in terms of acidity and hydrophobicity. The incorporation of different zirconium amounts into the mesostructured silica network creates Lewis and Bronsted acid surface sites allowing to control the surface properties of the mesoporous matrix and therefore the amount of phosphonate adsorbed into the mesopores. This effect occurs even at low ZrO2 contents and produces a noticeable modification on the release behavior of bisphosphonates. The partial retention of the drug through phosphonates complexation by zirconium sites leads to a more sustained release of the drug. These bina...

Adsorption of difluoromethane on titanium dioxide: Investigation of the FTIR spectra and quantum-mechanical studies of the adsorbate–substrate structures

The interaction of difluoromethane (CH 2F 2) with the TiO 2 surface (P25 Degussa) at room temperature has been studied by Fourier-transform infrared spectroscopy for the first time. From the comparison between the adsorption characteristics and the gas-phase spectra it can be deduced that the molecule adsorbs through an acid–base interaction between one F atom and the surface Lewis acid site (Ti 4+) and an H-bond between the CH 2 group and the surface Lewis basic site (OH − or O 2−). In order to obtain more information about the orientation geometry and the variation of the molecular structural parameters, a quantum-mechanical investigation at DFT/B3LYP level has been also performed, considering the anatase (1 0 1) surface and focusing on the O 2− as Lewis basic site. The resulting adsorbate–substrate structures involve the formation of an acid–base interaction between one F atom and the Ti 4+ ion and differ for the number of the involved H-bonds. According to the scaled vibrational frequencies, the simulated adsorption model which better agrees with the experimental data corresponds to that in which the CH 2 group interacts with the surface by only one H-bond.

Defining Reactivity of Solid Sorbents: What Is the Most Appropriate Metric?

A series of solid sorbent materials, including alumina (Al2O3), magnesia (MgO), titania (TiO2), silica (SiO2), and carbon, of widely varying physical properties, have been studied as sorbents for two toxic substances: sulfur dioxide gas (SO2) and chemical warfare surrogate 2-chloroethyl ethyl sulfide (2-CEES, ClCH2CH2SCH2CH3). Sorbent surface areas, average pore sizes, pore volumes, surface hydroxyl groups, and nitrogen adsorption−desorption isotherms were measured. Surface areas varied from 18 m2/g to over 1000 m2/g, pore volumes from 0.04 to 1.2 cm3/g, and pore diameters from 1.7 to 4.9 nm. Breakthrough studies of SO2 and 2-CEES sorption yielded information about the effectiveness of each sorbent. Carbon samples worked well for 2-CEES but not SO2, while silica samples were poor for both. The best MgO and TiO2 samples were good for both SO2 and 2-CEES, and overall, the highest surface area (459 m2/g) TiO2 sample was the superior sorbent. The important features for an effective sorbent under the conditions employed are high surface area and high pore volume, possessing isolated surface −OH groups, mesoporous nature, and a polar surface (Lewis base and Lewis acid sites).

Highly ordered mesoporous titania–zirconia photocatalyst for applications in degradation of rhodamine-B and hydrogen evolution

We report a facile synthesis of highly ordered mesoporous titania–zirconia composites with broad Ti/Zr ratios via an evaporation-induced self assembly (EISA) process. Amphiphilic poly(alkylene oxide) block copolymers, P123 and F127, serve as structure-directing agents (SDAs). By adjusting initial molar ratios of copolymer to metal precursors, titania–zirconia nanocomposites with controlled texture and composition are obtained in a wide range from 10 to 90 mol% TiO 2. Small-angle X-ray diffraction (SAXRD) and transmission electron microscopy (TEM) measurements reveal the two-dimensional (2D) hexagonal mesostructure ( p6 mm) with large-domain regularity. These mesostructured composites possess large surface areas and pore volumes, narrow pore size distributions, and abundant surface Lewis acid sites, resulting in unique photocatalytic activities for degradation of rhodamine-B and hydrogen evolution in methanol aqueous solution. Their good photocatalytic abilities are ascribed to the cooperative effect of the porosity and crystallinity.

Chemisorption Pathways and Catalytic Olefin Polymerization Properties of Group 4 Mono- and Binuclear Constrained Geometry Complexes on Highly Acidic Sulfated Alumina

Mono- and binuclear “constrained-geometry catalyst” (CGC) group 4 hydrocarbyls Me2Si(Me5C5)(tBuN)ZrMe2 [CGCZrMe2, 1], 1-Me2Si(3-ethylindenyl)(tBuN)ZrMe2 [EICGCZrMe2; Zr1, 2], (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2, Zr2, 3], and (μ-CH2CH2-3,3′){(η5-indenyl)[1-Me2Si-(tBuN)](TiMe2)}2 [EBICGC(TiMe2)2, Ti2, 4] undergo rapid chemisorption on highly Brønsted acidic sulfated alumina (AlS) surfaces. 13C CPMAS NMR spectroscopy of the chemisorbed 13CαH3-enriched complexes EICGCZr13Me2/AlS (2*/AlS) and EBICGC(Zr13Me2)2/AlS (3*/AlS) reveals that chemisorption involves two processes, M−C σ-bond protonolysis at the strong surface Brønsted acid sites and heterolytic M−C scission with methide transfer to strong surface Lewis acid sites, forming similar “cation-like” electrophilic organo-group 4 complexes such as EICGCM13Me+. Relative rates of ethylene homopolymerization mediated by the catalysts prepared via chemisorption on AlS are 4/AlS > 2/AlS > 3/AlS > 1/AlS, for ethylene polymerization at 75 psi ethylene and 25 °C. Ethylene/1-hexene copolymerizations mediated by the same set of catalysts display relative polymerization rates of 4/AlS > 3/AlS > 2/AlS > 1/AlS, for copolymerizations at 75 psi ethylene, 0.8 M 1-hexene, and 25 °C.

WOx effect on the catalytic properties of Pt particles on Al 2O 3

The effect of WOx on the microstructure, Lewis acidity and catalytic conversion of Pt/Al 2O 3 catalysts was studied. High surface areas were obtained at low W concentration and the WOx species decreased the Al 2O 3 surface area and Lewis acid sites. WOx species in tetrahedral coordination were found. Multiple layers of close-packed spheres forming pores were seen on the Al 2O 3. The addition of WOx produced semi-cubic particles and the spheres disappeared. At low W concentrations (0.5–2 wt%W) dehydrociclization and isomerization selectivities were higher than the hydrocracking selectivity. On the contrary high hydrocracking selectivity was found for samples with high W concentration (4–22 wt%W).

Structure and acid-base properties of hexaaluminates

Hexaaluminates SrAl12O19, BaAl12O19 and LaAl11O18 were prepared by co-precipitation of soluble nitrates of Sr, Ba, or La and Al using NH4HCO3 as a precipitating agent with subsequent calcination at 700–1400°C. The samples were characterized by adsorption methods, thermal analysis (TA and DTG), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy of adsorbed probe molecules (CO and CDCl3). It was shown that calcination at 1200°C resulted in the formation of single-phase hexaaluminates in all the samples except for LaAl11O18, where an additional phase was found. The specific surface area of the samples was obtained in the range 16–22 m2/g. After the treatment at comparable conditions, the total concentrations of both surface Lewis acid sites and basic sites were found to increase in the series: BaAl12O19 < SrAl12O19 < LaAl11O18. However, the strongest basic sites were detected on the surface of BaAl12O19.

Facile Synthesis for Ordered Mesoporous γ-Aluminas with High Thermal Stability

The facile synthesis of highly ordered mesoporous aluminas with high thermal stability and tunable pore sizes is systematically investigated. The general synthesis strategy is based on a sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous aluminas possess a highly ordered 2D hexagonal mesostructure, which is resistant to high temperature up to 1000 degrees C. Ordered mesoporous structures with tunable pore sizes are obtained with various precursors, different acids as pH adjustors, and different block copolymers as templates. These mesoporous aluminas have large surface areas (ca. 400 m2/g), pore volumes (ca. 0.70 cm3/g), and narrow pore-size distributions. The influence of the complexation ability of anions and hydro-carboxylic acid, acid volatility, and other important synthesis conditions are discussed in detail. Utilizing this simple strategy, we also obtained partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor. FTIR pyridine adsorption measurements indicate that a large amount of Lewis acid sites exist in these mesoporous aluminas. These materials are expected to be good candidates in catalysis due to the uniform pore structures, large surface areas, tunable pore sizes, and large amounts of surface Lewis acid sites. Loaded with ruthenium, the representative mesoporous alumina exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.

A Comparative Study on Aluminium Pillared Smectite Synthesis From Synthetic Saponite and Indonesian Montmorillonite

Synthesis of aluminium pillared smectite from two raw clays, saponite and Indonesian montmorillonite, has been investigated. The clays were characterized by XRD, N2 adsorption isotherm, DTA-TGA, surface acidity measurements using pyridine-FTIR method, and evaluated for catalytic esterification reaction. The characterization indicated an increase in d001 by metal oxide pillar, increase in BET specific surface area, and surface acidity. DTA-curves showed exothermic peaks in the range of 100-130oC and 400-800oC. TGA curves showed an increase in thermal stability of pillared clays. For both kinds of clays, it was also observed that pillarization reduced weight loss at high temperature. Esterification reaction rate constant and surface acidity data showed that the Bronsted acidity dominantly affects the reaction mechanism compared with the effect of specific surface area and Lewis acid site. Montmorillonite and pillared montmorillonite exhibited higher catalytic activity than saponite and pillared saponite although the specific surface areas of the latter are higher.

A Comparative Study on Aluminium Pillared Smectite Synthesis From Synthetic Saponite and Indonesian Montmorillonite

Synthesis of aluminium pillared smectite from two raw clays, saponite and Indonesian montmorillonite, has been investigated. The clays were characterized by XRD, N2 adsorption isotherm, DTA-TGA, surface acidity measurements using pyridine-FTIR method, and evaluated for catalytic esterification reaction. The characterization indicated an increase in d001 by metal oxide pillar, increase in BET specific surface area, and surface acidity. DTA-curves showed exothermic peaks in the range of 100-130oC and 400-800oC. TGA curves showed an increase in thermal stability of pillared clays. For both kinds of clays, it was also observed that pillarization reduced weight loss at high temperature. Esterification reaction rate constant and surface acidity data showed that the Bronsted acidity dominantly affects the reaction mechanism compared with the effect of specific surface area and Lewis acid site. Montmorillonite and pillared montmorillonite exhibited higher catalytic activity than saponite and pillared saponite although the specific surface areas of the latter are higher.

Study on Copper-based Catalysts for Synthesis of N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine from Reductive Alkylation of p-Nitroaniline with 5-Methyl-2-hexanone

The reductive alkylation of p-nitroaniline with 5-methyl-2-hexanone over copper-based catalysts was investigated. Furthermore, the catalysts were characterized using the techniques of XRD, H2–N2O titration, H2-TPR, NH3-TPD and pyridine-FTIR. The results showed that the addition of Mn, Ba and La into Cu–SiO2 catalyst played an important role in the improvement of the selectivity towards N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine (BMPPD). The highest selectivity towards BMPPD over 58CuO–9MnO2–BaO–1La2O3–30SiO2 (wt.%) catalyst could be ascribed to the best dispersion of copper (i.e., the highest hydrogenation ability) and the most amounts of the surface Lewis acidic sites.

Heterogeneous catalytic ozonation of benzothiazole aqueous solution promoted by volcanic sand

This paper presents experimental results on the catalytic effect of volcanic sands on benzothiazole ozonation. Experiments were assessed at laboratory scale, in a differential circular flow reactor composed of a volcanic sand fixed bed column of 19 cm 3 and a 1 dm 3 storage tank, operated in batch mode at 20 °C and pH 2–7. Experimental results show that ozone self-decomposition is enhanced by the presence of volcanic sand at all pH. At pH > pH PZC, the increase in aqueous ozone decay could be related to ozone interaction with strong Lewis acid on metal oxide surface sites of the volcanic sand. Ozone self-decomposition reactions occurring on the volcanic sand are less affected by the presence of radical scavengers. Benzothiazole removal by ozonation is also enhanced by the presence of volcanic sand. Moreover, the inhibitory effect of free radical scavengers is also impaired by volcanic sand, suggesting that strong Lewis acid surface sites play a key role on the reaction mechanism.

Study on Ni-Re-K/Al2O3 catalysts for synthesis of N,N′-di-sec-butyl p-phenylene diamine from p-nitroaniline and 2-butanone

Abstract Ni-Re-K/Al 2 O 3 catalysts used in reductive alkylation of p -nitroaniline with 2-butanone were investigated by means of BET, XRD, H 2 -TPR, NH 3 -TPD and pyridine-FTIR techniques. The results showed that the reducibility and the number of surface Lewis acidic sites of the catalysts played a significant role in improving their activities and selectivities. 10Ni-1Re-1K/Al 2 O 3 (γ-Al 2 O 3 calcined at 1173 K) exhibited better reducibility and the proper amount of surface Lewis acidic sites, so it performed the highest selectivity towards N , N ′-di- sec -butyl p -phenylene diamine among the catalysts.

Dehydration of Methanol to Dimethyl ether, Ethylene and Propylene over Silica-Doped Sulfated Zirconia

Two types of catalyst samples were prepared, one sulfated zirconia and the other silica doped sulfated zirconia. The acidity tests indicate that sulfated zirconia doped with silica has higher concentration and strength of acidic catalyst sites than undoped sulfated zirconia. The acidic surface sites have been characterized using FTIR, NMR, pyridine adsorption, TPD, XRD and nitrogen adsorption. Doping with silica increased the concentration of surface Lewis and Brfnsted acid sites and resulted in generation of proximate acid sites.The activity test indicates that doping sulfated zirconia with silica increases both the acidity and catalytic activity for liquid phase dehydration of methanol at 413-453 K. Methanol is sequentially dehydrated to dimethyl ether and ethylene over both catalysts. Significant amounts of propylene are also formed over the silica-doped catalyst, but not over the undoped catalyst.

Acid-base properties of alumina prepared from a hydrated product of centrifugal thermal activation of hydrargillite (cta-product)

Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides, representing γ-Al2O3, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was found to exceed their concentration in γ-Al2O3 prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides was lower than that in γ-Al2O3 prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits of 2.80-4.14 mmol/m2 and is essentially above that in g-Al2O3 (2.25 mmol/m2). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with nCO = 2220 and 2238 cm-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al2O3, however, in contrast to g-Al2O3,they contain strong basic sites with nCDCl3 = 2200 cm-1.