Surface OH Groups Research Articles

Chemistry of Desiccant Properties of Carbohydrate Polymers as Studied by Near-Infrared Spectroscopy

The combination frequency of water molecule in near-infrared spectroscopy is very useful for studying water molecular adsorption on solid surfaces. The absorption is purely from water molecules, and the variation in the absorption bands reflects the change in the environment of the water molecules on a surface. This variation, in turn, reflects the nature of the functional groups on the surface. Recently, Christy used this information in combination with second-derivative techniques to probe the surface of hydrothermally treated silica gel samples (Ind. Eng. Chem. Res.2011, 50, 5543). In this work, a similar approach was used in studying the surface OH groups in carbohydrate polymers and their behavior toward water molecular adsorption. Not only second-derivative profiles but also fourth-derivative profiles of the near-infrared spectra were used in revealing the adsorption behavior of the OH groups on the polymer surface. Carbohydrate polymers such as amylose amylopectin, cellulose, and starch samples were used in this study. After being heated and evacuated at 120 °C, the samples were exposed to air, and the evolving changes on the surfaces of the samples were followed by near-infrared spectroscopy. Furthermore, the effectiveness of the samples in adsorbing water molecules was followed by monitoring the mass of water adsorbed. These investigations formed the basis for understanding how the OH groups on the carbohydrate polymers adsorb water molecules. The results clearly reveal that carbohydrate polymers such as amylose, amylopectin, and cellulose have three OH groups of different polarities and that the OH groups attached to C2 and C3 positions in the monomer glucose units adsorb water molecules faster than the C6-OH group. Furthermore, the adsorption of water molecules in amylose and amylopectin follows the same pattern during the first hour, irrespective of the variation in their structure.

Synthesis of Hydrophobic Silica Nanopowders

The technique of receiving of nano-silica nanopowders, consisting of nanoparticles with the known size, form, internal and surface structure and physicochemical properties was developed. The degree of hydrophilicity of those powders was determined. The method of the surface modification (hydrophobization) of the received nanoparticles was carried out and was optimized. Replacement of surface OH-groups on the CH3-group was produced by blowing SiCl2(CH3)2 vapor over the modified powders surface. The carbon content of the modified powders reached 3.2 %. The comparison of the hydrophobization process for the nanopowders received by two different origins was carried out. It was shown that the surface modification of Aerosil powders is faster than Tarkosil ones at similar hydrophilicity degree. Also hydrophobiс Aerosil contains more amount of carbon was cleared (up to 5,9 %). The complete replacement of OH-groups on the organic groups on the surface of powders was showed by IR spectroscopy. The representation of the organic groups by several combinations of fragments, rather than just the CH3 was showed

Kinetics of aluminum extraction from Ti3AlC2 in hydrofluoric acid

Herein we report on the influence of particle size, time and temperature on the kinetics – quantified by X-ray diffraction – of the selective extraction of Al from the ternary layered transition metal carbide, Ti3AlC2, when powders of the latter are immersed in hydrofluoric acid. Transmission and scanning electron microscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis were also used to characterize the resulting powders. Increasing the temperature and immersion times, and decreasing the Ti3AlC2 particle size, led to faster conversion of Ti3AlC2 to its 2-D Ti3C2 counterpart. Arch-shaped edges at the ends of some Ti3C2 layers resembled graphene, corroborating the single-sheet structure of exfoliated Ti3C2. The removal of water and/or OH surface groups from Ti3C2 using drying in vacuum was also attempted.

An ionic liquid route to prepare mesoporous ZrO2–TiO2 nanocomposites and study on their photocatalytic activities

Mesostructured ZrO2–TiO2 nanoparticles with different ZrO2 contents have been synthesized by an ionic liquid-assisted hydrothermal route. The prepared materials were characterized by means of X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra analysis (DRS) and NH3-TPD technique. The obtained ZrO2–TiO2 materials exhibit large specific surface area and uniform pore sizes. Introduction of ZrO2 species can effectively suppress phase transformation from anatase to rutile and promote thermal stability of ZrO2–TiO2 materials. The photocatalytic activity of the ZrO2–TiO2 sample is higher than that of the TiO2 sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the ultraviolet region, higher specific area, smaller crystal size and increased surface OH groups.

Effects of controlled SiO2 deposition and phosphorus and nickel doping on surface acidity and diffusivity of medium and small sized HZSM-5 for para-selective alkylation of toluene by methanol

In this work the controlled SiO2 deposition on the HZSM-5 of medium (M-) and small (S-) sized grains is accomplished through the mild steam-pretreatment of zeolites (to modify the density of surface OH groups) followed by chemical liquid deposition (CLD) process. The amount of deposited SiO2 is tunable by varying the conditions of steam-pretreatment and/or CLD process, which allows quantitative correlating the changes of sample characteristics with the amount of deposited SiO2. NH3-TPD, pyridine and 2,6-DBT-pyridine adsorption infrared spectroscopic studies revealed the effect of surface SiO2 deposition on strength (weak and strong), type (Brønsted and Lewis), and location (external) of acid sites of HZSM-5. The external Brønsted acid sites of more than 75% are diminished upon SiO2 deposition of 13wt%. Due to pre-existing extra Na+ in S-HZSM-5, less amount of SiO2 deposition or P-doping will cause more obvious enhancement in para-selectivity on S-HZSM-5. The present study revealed that with the integrated modifications of SiO2 deposition and P–Ni doping on S-HZSM-5, toluene conversion of 31% and para-selectivity of 91% can be achieved. It was also found that doping of 5wt% Na and 6wt% P to M-HZSM-5 (free of silylation) can give p-xylene selectivity of ∼80% at toluene conversion of ∼26%. SiO2 deposition can more obviously reduce the strong acid sites, and P–Ni doping seems also to affect Lewis acidity. Low density of Brønsted (external)/Lewis acid sites and controlled diffusivity of HZSM-5 would be favorable for p-xylene generation in toluene alkylation with methanol.

Alkali Metal Modification of Silica Gel-Based Stationary Phase in Gas Chromatography

Modification of the precipitated silica gel was done by treatment with alkali metal (NaCl) before and after calcination. The silica surfaces before and after modification were confirmed by infrared spectroscopy in order to observe the strength and abundance of the acidic surface OH group bands which play an important role in the adsorption properties of polar and nonpolar solutes. The surface-modified silica gels were tested as GC solid stationary phases in terms of the separation efficiency for various groups of non-polar and polar solutes. Also, thermodynamic parameters (<svg style="vertical-align:-0.0pt;width:25.924999px;" id="M1" height="11.425" version="1.1" viewBox="0 0 25.924999 11.425" width="25.924999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><path id="x394" d="M600 0h-557v24l268 633l28 8l261 -641v-24zM497 50l-194 489l-196 -489h390z" /></g><g transform="matrix(.017,-0,0,-.017,10.959,11.363)"><path id="x1D43B" d="M865 650q-1 -4 -4 -14t-4 -14q-62 -5 -77 -19.5t-29 -82.5l-74 -394q-12 -61 -0.5 -77t75.5 -21l-6 -28h-273l8 28q64 5 82 21t29 76l36 198h-380l-37 -197q-11 -64 0.5 -78.5t79.5 -19.5l-6 -28h-268l6 28q60 6 75.5 21.5t26.5 76.5l75 394q13 66 2 81.5t-77 20.5l8 28&#xA;h263l-6 -28q-58 -5 -75.5 -21t-30.5 -81l-26 -153h377l29 153q12 67 2 81t-74 21l5 28h268z" /></g> </svg>, <svg style="vertical-align:-0.23206pt;width:23.325001px;" id="M2" height="11.75" version="1.1" viewBox="0 0 23.325001 11.75" width="23.325001" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D43A" d="M713 296l-5 -25q-47 -7 -59 -20t-23 -72l-15 -79q-9 -48 -3 -74q-15 -3 -55 -13t-63 -15t-59.5 -10t-70.5 -5q-149 0 -243 80t-94 220q0 169 127.5 276.5t336.5 107.5q91 0 206 -36l-10 -165l-29 -1q1 85 -47.5 126t-146.5 41q-153 0 -243.5 -97t-90.5 -242&#xA;q0 -122 68.5 -198.5t188.5 -76.5q121 0 139 75l20 86q13 58 -1.5 70.5t-99.5 20.5l5 26h267z" /></g> </svg>, and <svg style="vertical-align:-0.23206pt;width:19.174999px;" id="M3" height="11.75" version="1.1" viewBox="0 0 19.174999 11.75" width="19.174999" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.4)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.4)"><path id="x1D446" d="M457 488l-30 -3q-17 148 -131 148q-53 0 -84.5 -34.5t-31.5 -82.5q0 -42 25.5 -72t74.5 -62l33 -22q63 -42 95 -85t32 -102q0 -84 -67 -137t-163 -53q-58 0 -113 22t-70 43l-4 152l27 4q4 -32 15 -62.5t31 -59.5t53.5 -47t76.5 -18q56 0 92 35t36 96q0 39 -25 70t-78 68&#xA;l-31 22q-32 23 -53.5 41.5t-45 57t-23.5 77.5q0 82 58 132.5t156 50.5q46 0 101 -17l18.5 -6t17 -6t8.5 -3q-4 -55 0 -147z" /></g> </svg>) were determined using <i >n</i>-hexane as a probe in order to show the adsorbate-adsorbent interaction. It was observed that the non-polar solutes could be separated Independent on the reactivity and porosity of the silica surfaces. The efficiency of the surface-modified silica gels to separate the aromatic hydrocarbons seemed to be strongly influenced by the density of the surface hydroxyls.

Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles

Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanoparticles of hematite (α-Fe2O3), maghemite (γ-Fe2O3), and goethite (α-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Brønstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy CO bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Brønstedt acid sites).

Preparation and characterisation of γ-Al2O3 particles-supported Rh/Ce0.9Pr0.1O2 catalyst for N2O decomposition in the presence of O2, H2O and NOx

A supported catalyst composed by the active phase Rh/Ce0.9Pr0.1O2 loaded on γ-Al2O3 particles was prepared and characterised by SEM, TEM, XRD, Raman spectroscopy, N2 adsorption at −196°C, H2-TPR and XPS. The catalytic decomposition of N2O was studied in simulated nitric acid plant streams (in the presence of O2, H2O and/or NOx) both in a fix-bed reactor and by in situ DRIFTS-MS experiments. The supported catalyst is able to decompose N2O from around 350–400°C in the presence of O2, H2O and/or NOx, and this temperature would be enough to decompose N2O in a nitric acid production plant after the expansion turbine, avoiding the use of an additional energy input. Among O2, H2O and NOx, NOx is the strongest inhibitor and O2 the weakest. The inhibiting effect of O2 is attributed to its reversible chemisorption on catalyst active sites, while the effect of H2O and NOx is mainly related with their irreversible chemisorption. The inhibition of H2O is not as high as that of NOx because the product of H2O chemisorption (Ce–OH surface groups) is suitable for N2O chemisorption and decomposition, while the surface nitrogen species created upon NOx chemisorption are not.

Role of Water in Methanol Photochemistry on Rutile TiO2(110)

Photochemistry of the molecularly and dissociatively adsorbed forms of methanol on the vacuum-annealed rutile TiO2(110) surface was explored using temperature-programmed desorption (TPD) both with and without coadsorbed water. Methoxy, and not methanol, was confirmed as the photochemically active form of adsorbed methanol on this surface. UV irradiation of methoxy-covered TiO2(110) led to depletion of the methoxy coverage and to formation of formaldehyde and a surface OH group. Coadsorbed water did not promote either molecular methanol photochemistry or thermal decomposition of methanol to methoxy. However, terminal OH groups (OHt), prepared by coadsorption of water and oxygen atoms, thermally converted molecularly adsorbed methanol to methoxy at 120 K thus enabling photoactivity. While chemisorbed water molecules had no influence on methoxy photochemistry, water molecules hydrogen-bonded in the second layer to bridging oxygen (Obr) sites inhibited methoxy photodecomposition to formaldehyde. From this, we...

Super-hydrophobic fluorination mesoporous MCF/TiO2 composite as a high-performance photocatalyst

NH4F was used instead of conventional organic silylation agent as the hydrophobic modifier to synthesize the super-hydrophobic mesocellular foams (MCF) loaded with nano-sized TiO2 photocatalysts in its pore channels, which could be considered as an extractant for organics. Compared to organosilane modified catalysts, NH4F-modified MCF/TiO2 has a more stable super-hydrophobic property and much higher photocatalytic activity. It was found that only using isopropanol as the solvent, the NH4F-modified catalyst showed super-hydrophobic property. It is believed that the solvent plays a role in controlling the exchange between surface OH groups and F ions. The special structure of supported mesoporous catalyst greatly facilitated the surface fluorination, which together with the Ti3+ generation led to its excellent adsorption capacity and UV/visible light photocatalytic activity. This novel super-hydrophobic mesoporous photocatalyst has a large application potential in the field of photocatalysis, shipbuilding, and other industries.

Pentylcyanobiphenyl as Test Molecule for the Acid Sites of Powdered Titanium(IV) Oxides: Sensitivity of Core Levels to the Local Structure

Pentylcyanobiphenyl was used successfully as a test molecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e.g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene π electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Brønsted acid sites.

Obtaining Some Polymer Composites Filled with Rice Husks Ash-A Review

Rice husks are an important by-product of rice milling process and are major waste product of the agricultural industry. Rice husk contain nearly 20 mass% silica, which is present in hydrated amorphous form. They have now become a great source as a raw biomass material for manufacturing of value-added silicon composite products, including silicon carbide, silicon nitride, silicon tetrachloride, magnesium silicide, pure silicon, zeolite, fillers of rubber and plastic composites, cement, adsorbent and support of heterogeneous catalysts. The rice husk was subjected to pyrolysis in fluidized-bed pilot plant in air or nitrogen atmosphere. The controlled thermal degradation of the rice husks in air or nitrogen leads to production of white rice husks ash (WRHA) and black rice husks ash (BRHA) respectively. WRHA contains almost pure (³95mass %) silica in a hydrated amorphous form, similar to silica gel, with high porosity and reactive surface OH groups. BRHA contains different amounts of carbon and silica in amorphous form with high specific surface area and porosity. The raw rice husks and the obtained pyrolysis products were used as fillers of polypropylene (PP) and tetrafluoroethylene-ethylene copolymer (TFE-E) composites. The kinetics and thermodynamics of water adsorption onto filled polypropylene composites during soaking were studied at different temperatures, quantities and nature of fillers. It was established, that the adsorption kinetics was limited by intra-particle diffusion in plane sheet particles. The sorption process is exothermal in nature and accompanied with decrease of the entropy. The physicomechanical properties of composite materials were determined. The fillers introduced in polypropylene change the mechanical strength and make the composites brittle. This change is more pronounced for the composites with BRHA and RRH, followed by WRHA. The composites studied showed lower elongation at break. The biggest decrease was observed for the composites with BRHA where ? decrease from 500 (for the initial PP) to 7 % at filling degree of 20 mass %. The effects of the amount of adsorbed water, temperature and treatment time on the composites tensile properties were estimated. It was found after immersion in water that the composites improve their tensile strength compared to initial non-treated samples. The thermal stability and kinetics of non-isothermal degradation of PP and TFE-E composites filled with 10 or 20 mass % vigorously grounded and mixed RRH, BRHA, WRHA and Aerosil Degussa (AR) were studied. Using different calculation procedures the most probably kinetic mechanism was found to be described by kinetic equations of n-th order (Fn mechanism). The kinetic parameters were obtained, and a linear dependence between ln A and E was observed, known also as kinetic compensation effect. The abundance of a waste from paddy milling industry, as well as its interesting complex of behaviors are prerequisite for success for obtaining of cheap and valuable products and gives a new alternatives for its applications. The production of value added materials from rice husks not only facilitates utilization of an abundantly available agro waste, but also reduces the environmental pollution and solves a serious ecological problem.

Hydrogen Adsorption and Site-Selective Reduction of the Fe3O4(001) Surface: Insights From First Principles

Density functional theory calculations including an on-site Hubbard term are used to explore hydrogen adsorption on the surface of Fe3O4(001). The adsorption energy exhibits a minimum for two hydrogen atoms per (√2 × √2)R45° surface unit cell and gets less favorable with increasing hydrogen coverage due to OH–OH repulsion. Terminations with two and four hydrogen atoms per surface unit cell are stable for moderate to high partial pressures of O and H. The strong tilt of the OH bond parallel to the surface facilitates hydrogen bonding to neighboring oxygen and hopping of the protons between surface oxygen sites. Furthermore, the formation of surface OH groups leads to a monotonic reduction of work function with increasing H coverage. The analysis of the electronic properties reveals selective switching of neighboring surface and subsurface Fe from Fe3+ to Fe2+ upon hydrogen adsorption. This provides a promising way to tune the catalytic activity of the Fe3O4(001) surface.

Chemical exchange and spectral coalescence in low-hydration MCM-41 studied by proton NMR

In Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, involving silica-based porous media, containing surface OH groups and water, it is generally observed that the water proton and OH group proton resonances tend to coalesce with increasing moisture content. It has been suggested that chemical exchange between protons of surface OH groups and water may not be the only mechanism producing the coalescence in the mesoporous material MCM-41. [Chem. Eur. J. 10 (2004) 5689] Here the importance of such exchange was investigated in MCM-41, hydrated to one water molecule per OH group, using low-field, static NMR relaxation techniques and high-field MAS NMR techniques. First the surface-water chemical exchange rate was estimated from two dimensional time domain NMR selective inversion recovery experiments. Second the exchange rate required to produce coalescence was estimated by modeling the exchange spectra using expected water proton NMR spectral positions and surface OH proton NMR spectral positions obtained from MAS experiments in dry MCM-41. The results suggest that the surface-water chemical exchange rate is too small to produce substantive proton NMR spectral coalescence in the MCM-41 material at this hydration level.

Environment-Controlled Tethering by Aggregation and Growth of Phosphonic Acid Monolayers on Silicon Oxide

Phosphonic acid monolayers are being considered as versatile surface modification agents due to their unique ability to attach to surfaces in different configurations, including mono-, bi-, or even tridentate arrangements. Tethering by aggregation and growth (T-BAG) of octadecylphosphonic acid (ODPA) on silicon oxide surfaces has proven to be a robust method to establish a strong chemical bond. However, it requires a long processing time (> 48 h) that is a substantial drawback for industrial applications. We demonstrate here that the humidity level during processing is the most important parameter controlling the reaction. Using in situ Fourier Transform Infrared Spectroscopy (FTIR), we first show that the initially physisorbed layer obtained upon immersion in ODPA is composed of well-ordered bilayers and only reacts with the SiO(2) surface at 140 °C. Importantly, we show that the presence of water at the interface (determined by the humidity level) greatly influences the reaction time and completion. In humid environments (relative humidity, RH > 40%), there is no reaction, while in dry environments (RH < 16%), the reaction is essentially instantaneous at 140 °C. Ab initio calculations and modeling confirm that the degree of chemical reaction with the surface OH groups depends on the chemical potential (i.e., concentration) of interfacial water molecules. These findings provide a workable modification of the traditional T-BAG method consistent with many industrial applications.

탄소나 TiO2를 포함한 다양한 흡착제의 휘발성 유기물 흡착에 대한 연구

본 연구에서는 톨루엔 등의 휘발성 유기물의 흡착량을 정성, 정량적으로 연구할 수 있는 새로운 장비를 구축하였으며, 이를 이용하여 기존의 탄소를 기반으로 하는 다양한 흡착제와 원자층 증착으로 만든 <TEX>$TiO_2$</TEX> 박막구조의 톨루엔 흡착에 대한 연구를 진행하였다. <TEX>$TiO_2$</TEX> 박막구조의 흡착제가 기존의 탄소기반 흡착제보다 톨루엔 흡착량이 뛰어난 것을 입증하였으며, 이는 원자층증착으로 제조한 <TEX>$TiO_2$</TEX> 박막 표면의 높은 농도의 OH 그룹의 높은 톨루엔 친화력과 연관성이 있는 것으로 나타났다. 또한 본장비를 이용하여 가역적인 흡착과 비가역적인 흡착을 구분할 수 있음을 보여주었다. New equipment for quantitative and qualitative adsorption of volatile organic compound was set up, and using this equipment, adsorption behaviors of various carbob-based nanomaterials and <TEX>$TiO_2$</TEX> thin films prepared by atomic layer deposition were compared. We could conclud that <TEX>$TiO_2$</TEX> thin films can show higher adsorption capacity of toluene comparing to the carbon-based nanostructures due to higher affinity of the surface OH groups of <TEX>$TiO_2$</TEX> towards toluene adsorption. We also demonstrate that our method allows to discriminate reversible and irreversible adsorptions at a given temperature.

Support and alloy effects on activity and product selectivity for ethanol steam reforming over supported nickel cobalt catalysts

Ni, Co and bimetallic Ni–Co catalysts supported on Ca-γ-Al2O3 and ZrO2 were investigated for the production of hydrogen via ethanol steam reforming (ESR). Catalysts were prepared by wet impregnation method and characterized using temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). ESR and temperature-programmed desorption of ethanol (ethanol-TPD) were carried out in a continuous flow fixed bed micro-reactor and the outlet gases were monitored by an on-line GC or MS. Ni is found to be more active for the C–C bond rupture than Co on both supports, Ca-γ-Al2O3 and ZrO2. Catalyst support plays very important roles for the ESR. Strong interaction between support and metal affects the formation of NiCo bimetallic compound, resulting in the variety of catalytic activity. On Ca-γ-Al2O3 support, the catalytic activity of ESR follows the sequence of 10%Ni > 6.7%Ni 3.3%Co ∼ 3.3%Ni 6.7%Co > 10%Co. On ZrO2, the trend is 10%Ni > 6.7%Ni 3.3%Co > 10%Co > 3.3%Ni 6.7%Co. The H2O adsorption/activation ability of the support determines the reaction pathway and thus the product selectivity. On Ca-γ-Al2O3, water gas shift reaction is more favorable than on ZrO2, due to the availability of surface OH groups. The roles of the metal and support for ESR are also discussed.

Atomic structure, comparative stability and electronic properties of hydroxylated Ti2C and Ti3C2 nanotubes

Recently, hydroxylated and fluorinated graphene-like titanium carbide TiCx layers have been solvothermally fabricated in large amounts from so-called MAX phase Ti3AlC2. We assume, that a wide family of novel planar and tubular forms of titanium carbides may exist and design the atomic models for monolayers and nanotubes with nominal stoichiometry Ti2C, Ti3C2 and for their hydroxylated forms Ti2C(OH)2, Ti3C2(OH)2. The stability and electronic properties of these nanostructures are examined by means of density-functional theory tight-binding method depending on the composition and the type of OH arrangement. We reveal that the type of OH termination plays a minor role in the variation of nanotubes’ strain energies, but causes a difference in the relative stability of their parent planar phases. The electronic structure for all nanotubes studied has metallic-like character, while their precursors (planar layers) demonstrate either metallic-like or semiconducting behavior depending on the arrangement of the surface OH groups.

Au/FeOx catalysts of different degree of iron oxide reduction

Au/FeOx catalysts were prepared by deposition of Au on Fe3O4 (commercial Cerac, a mixture of magnetite and maghemite) with the deposition-precipitation method, and heating of the precursors in air or in Ar. The catalysts were characterized by XPS, Mössbauer spectroscopies, H2TPR, TEM, decomposition of isopropanol (probe reaction for acid–base properties), and tested in CO oxidation.The heating atmosphere influences composition, physicochemical and catalytic properties. The catalysts prepared in Ar contain magnetite, MT and maghemite, MG as the main iron oxide phases, for those calcined in air MG is the only phase observed. Higher amounts of weakly bound oxygen are observed in H2TPR measurements for the catalysts prepared in air. They exhibit smaller acidity and higher basicity compared to the samples prepared in Ar. The mean particle size of nano Au is not affected markedly by the preparation conditions and amounts to ∼4.5nm. Calcination in Ar appears, however, to stabilize smaller particles (<4nm) against the sintering. Catalytic activity of the Au/FeOx catalysts in CO oxidation is higher for catalysts prepared in air, containing MG, as compared to those containing MT. This can be related to the higher amounts of weakly bound oxygen for the former catalysts. In the reaction mixture CO+O2, MT phase is oxidized to MG. For all the catalysts the activity is considerably enhanced by pretreatment in hydrogen. This can be associated with the increase in the content of the surface OH groups.

Operando DRIFTS study of the role of hydroxyls groups in trichloroethylene photo-oxidation over titanate and TiO2 nanostructures

The aim of the present research was to gain further insight into the differences of the trichloroethylene photodegradation routes when using TiO2 (Degussa P25) and protonated titanate nanotubes (H2Ti3O7). These last materials have structural hydroxyls that, along with the surface OH groups present in both photocatalysts, could mediate in the mineralization of the pollutant. In order to obtain a realistic view, an operando Diffuse Infrared Fourier Transform Spectroscopy (DRIFTS) approach has been adopted for surface analysis during the photocatalytic oxidation. The study revealed that the mineralization yield of trichloroethylene on the titanate nanotubes calcined at 300°C was better than the one obtained with the benchmark photocatalyst Degussa P25. In particular, the synthesized nanotubes showed the selective removal of some specific hydroxyl groups, suggesting that their high density and, probably, the specific characteristics of their hydroxyl species can be responsible for the enhanced dechlorination photoactivity exhibited by these nanotubular structures.