Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

Fractional-hydrolysis-driven formation of non-uniform dopant concentration catalyst nanoparticles of Ni/CexZr1 − xO2 and its catalysis in methanation of CO2

Ni/ceria–zirconia solid solution (Ni/Ce_xZr_1 − xO₂) with Ce and Ni enriched on the surface of the catalysts are prepared via a simple, low-cost method. The aqueous phase reactions simplify the preparation process, save the cost and lead the Ce to enriching on the surface of products. The impregnation method makes the Ni enriching on the surface of products which enhances the efficiency of active component. These catalysts exhibit significantly high catalytic performance. The formation mechanism is also investigated.     

Relation between surface acidity and reactivity in fructose conversion into 5-HMF using tungstated zirconia catalysts

Catalytic dehydration of fructose and its conversion to 5-hydroxymethylfurfural was studied using tungstated zirconia oxides, with various tungsten oxide loadings (1–20 wt.%). The samples were prepared by incipient wetness impregnation and thoroughly characterized using a combination of different techniques: structural, thermal and calorimetric analyses. Zirconia was predominantly present in the investigated samples in the tetragonal phase when the WO₃ loading was above 10 wt.%. The samples exhibited amphoteric characteristics, as they adsorbed both ammonia and sulfur dioxide on their surface. The number of surface acid sites increased with increasing WO₃ content. Fructose dehydration tests evidenced the formation of 5-hydroxymethylfurfural and by-products (formic and levulinic acids). The results show that the ratio of basic to acidic sites of the solid catalysts is the key parameter for the selectivity in 5-HMF, while the global fructose conversion was mainly related to the presence of acid sites of a given strength with 150 > Q_diff > 100 kJ·mol_NH3^− 1.     

Characterization of catalysts in their active state by adsorption microcalorimetry: Experimental design and application to sulfated zirconia

A method to characterize the surface sites of catalysts in their active state by adsorption microcalorimetry was developed. A calorimeter cell was used as a flow-type reactor, and the skeletal isomerization of n-butane (1 kPa) at 378 K and atmospheric pressure proceeded at comparable rates and with the same states of induction period, maximum and deactivation phase as in a tubular reactor. The reaction was run for selected times on stream and after the removal of weakly adsorbed species, n-butane or isobutane were adsorbed at 313 K. The surface of activated sulfated zirconia was characterized by at least two different sites for n-butane adsorption, a small group of sites (about 20 μmol g^?1) that yielded heats of 50–60 kJ mol^?1 and sites that were populated at higher pressures (above about 5 hPa n-butane) and yielded heats of about 40 kJ mol^?1. The strongly interacting sites disappear during the induction period and are proposed to be the sites where the isomerization reaction is initiated.     

Structural,mechanical and biological properties of hydroxyapatite-zirconia-lanthanum oxide composites

Novel hydroxyapatite-zirconia-lanthanum oxide composites for bioceramic applications were synthesized and their structural, mechanical and biological properties were studied. Pure HA was produced via precipitation method and the composites were obtained by several fabrication steps: powder milling, mixing, cold pressing and sintering at 1100 °C for 1 h. The experimental results indicated that the composites consisted of hydroxyapatite as the main phase with a trace amount of tricalcium phosphate. Calcium zirconate (CaZrO₃) was also formed by the reaction between zirconia and calcium oxide (CaO) which is the thermal decomposition product of hydroxyapatite. Addition of zirconia and lanthanum oxide resulted a more loose and porous structure on the surface. The diametral tensile strength of the composites was higher with respect to pure hydroxyapatite. The microhardness of the composites, except the one with the composition of 90 wt% HA and 10 wt% Zr, was relatively lower than that of pure HA but these composites had higher machinability. Cell culture studies with osteoblast-like Saos-2 cell line showed that composites and pure hydroxyapatite were biocompatible. Based on these findings, hydroxyapatite-zirconia-lanthanum oxide composites hold potential to be used in hard tissue replacement and regeneration therapies.     

Sucrose-mediated sol–gel synthesis of nanosized pure and S-doped zirconia and its catalytic activity for the synthesis of acetyl salicylic acid

Nano-sized pure and S-doped zirconia was prepared by the sol–gel method in the presence of sucrose and zirconium(IV) acetylacetonate (Zr(acac)₄) as a gelation agent and Zr⁴⁺ source, respectively. Acid catalyst activity of samples was tested for the production of acetyl salicylic acid from salicylic acid and acetic anhydride as precursors, The yield (64.0%) of acetylsalicylic acid was obtained from 50 mg of S-doped zirconia calcined at 550 °C and after a 3 h reaction, was comparably higher than the yield of the reaction (13.3%) in the absence of a catalyst and under the same reaction condition.     

Microwave assisted solvent free synthesis of α,ά-bis (arylidene) cycloalkanones by sulfated zirconia catalyzed cross aldol condensation of aromatic aldehydes and cycloalkanones

The catalytic application of sulfated zirconia as solid Brønsted acid catalyst was explored for cross aldol condensation reactions (Claisen Schmidt reaction). The synthesized catalyst was highly active for solvent free synthesis of α,?-bis(arylidene)cycloalkanones by cross aldol condensation of aromatic aldehydes with cycloalkanones. The microwave assisted synthesis resulted increased yields of the products (79–99%) at significantly lower reaction temperature (120–140 °C) and reaction time (20 min) as compared to the synthesis by thermal heating (63–96% yield at 170 °C after 4 h). The microwave irradiation afforded selectively cross aldol products. The catalyst could be easily regenerated and reused several times with similar efficiency.     

Graphitization at low temperatures (600–1200 °C) in the presence of iron implications in planetology

Our objective is to understand how graphite can be formed at “low” temperatures (<1200 °C) in contrast to the high temperature of the industrial processes (∼3000 °C), and from precursors which are non-graphitizable by a thermal treatment alone. Blends of iron and saccharose char were heated between 650 and 1600 °C. The carbons obtained were characterized by SEM, TEM and Raman microspectrometry. Our work confirms that graphite can be formed from non-graphitizable carbons during a heat-treatment in the presence of iron. Carbon and iron migrations, below the eutectic temperature (1150 °C), appear to be a key factor for carbon transformation. Iron migration and graphitization could be favored by nucleation of Fe nanoparticles and surface melting, detected as soon as 900 °C. This allows formation of turbostratic macroporous carbons. Above the eutectic, all iron is liquid and graphitization occurs; it is complete at 1600 °C. Heat-treatment duration, observed over 4 orders of magnitude, favors the structural improvement. Concerning applications in planetology these experimental samples are pertinent experimental analogues of natural carbons from differentiated parent-bodies (with an iron core), and explain how graphite can be formed at temperatures below 1200 °C in these environments.     

Novel supports for nickel-based catalysts for the partial oxidation of methane

Zirconia-supported nickel catalysts with different amounts of aluminum (Al/Zr = 0.2, 1 and 2) were studied in this work in order to find alternative supports for nickel-based catalysts for the partial oxidation of methane. This reaction is a promising route for producing hydrogen and syngas for different applications. Samples were prepared by precipitation and impregnation techniques, characterized by several techniques and evaluated in the partial oxidation of methane in the range of 450–750 °C and 1 atm. It was found that aluminum affects the textural and catalytic properties of zirconia-supported nickel catalysts. The tetragonal phase of zirconia was stabilized by aluminum and gamma-alumina was also found in the aluminum-richest samples. Aluminum increased the porosity and the specific surface area of the solids. The catalytic activity also increased with the amount of aluminum in solids probably due to the stronger interaction of nickel with the support, which slowly generates active sites during the reduction step. The methane conversion and hydrogen selectivity increased with temperature, indicating no deactivation. The hydrogen to carbon monoxide molar ratio decreased due to aluminum but was not significantly affected by temperature. The coke produced was not harmful to the catalysts and aluminum affected its amount, although no simple relationship was found between these parameters. The most promising catalyst was the sample with aluminum to zirconium molar ratio of 2, which showed high activity and hydrogen selectivity and was stable under the reaction condition.     

Template effect of single/double-chain quaternary ammonium salts on the formation of mesoporous ZrO2 nanomaterials

A double-chain quaternary ammonium salt of dioctyl dimethyl ammonium chloride (DDAC8) was first used as a low-cost template to prepare the mesostructured zirconia nanomaterials in an alcohol-thermal system. The material was calcinated to obtain pure tetragonal crystalline zirconia (t-zirconia) and thus has significantly improved original structure properties, including a narrow pore size distribution of 4–7 nm and a high surface area of 195 m²/g. The t-zirconia hierarchical nanoparticle aggregate material is different from the smooth microsphere material obtained using the single chain quaternary ammonium salt template. The characteristic rough surface morphology results from the grid distribution form of the DDAC8 micelles in the ethanol solution and caused the formation of more defect sites, which demonstrate the potential for possible catalytic applications. A formation mechanism of the mesoporous zirconia nanomaterial in the alcohol-thermal system of the surfactants is reasonably explained. The synthesis system may provide a new approach to the preparation of mesoporous nanomaterials.     

The dehydrogenation of ethylbenzene with CO2 over CexZr1 − xO2 solid solutions

With the purpose of changing the lattice structure of CeO₂ and improving the transmission capacity of lattice oxygen, Ce_xZr_1 − xO₂ solid solutions with different Zr proportions were synthesized using a hydrothermal method and applied in oxidative dehydrogenation of ethylbenzene to styrene with CO₂ at 550 °C. The Ce_0.5Zr_0.5O₂ showed the highest activity with an ethylbenzene conversion of 55% and styrene selectivity above 86%. Analytical characterization showed that the lattice oxygen mobile capacity of Ce_xZr_1 − xO₂ solid solutions was enhanced, corresponding to the order as Ce_0.3Zr_0.7O₂ > Ce_0.5Zr_0.5O₂ > Ce_0.7Zr_0.3O₂ > CeO₂. The oxygen storage/release capacity, higher surface area and pore distribution of Ce–Zr mixed oxides play important roles in the activity of ethylbenzene dehydrogenation to styrene with CO₂.     

Role of CeO2–ZrO2 in diesel soot oxidation and thermal stability of potassium catalyst

Potassium nitrate catalysts supported on different oxides (CeO₂, Ce_0.5Zr_0.5O₂ and ZrO₂) were prepared for diesel soot combustion. The ageing treatment was performed at 800 °C for 24 h and the catalytic activity was evaluated by a temperature-programmed oxidation technique. The results demonstrated that, compared with CeO₂ and ZrO₂, Ce_0.5Zr_0.5O₂ presented good redox properties, a high surface area and available potassium-holding capacity at an elevated temperature. For aged K/Ce_0.5Zr_0.5O₂, the combustion temperature of soot particle was 359 °C under tight contact conditions and 455 °C under loose contact conditions. Thus, ceria–zirconia mixed oxides were considered as good candidate supports for diesel soot oxidation catalysis.     

Monolithic acidic catalysts for the dehydration of xylose into furfural

We report the application of hierarchically porous zirconium phosphate monoliths with high surface area as acidic heterogeneous catalysts for the dehydration of xylose into furfural. Analyses by NH₃-temperature programmed desorption and ³¹P solid state NMR reveal the presence of both Lewis and Brønsted acid sites in the as-synthesized zirconium phosphate monolith and that calcined at 600 °C. High accessibility and availability of the acidic sites and easy separation of the monolith from the liquid medium result in good catalytic activity (initial reaction rate for furfural production as 8.7 mmol g_cat^− 1 h^− 1) with easy handling of the catalyst.     

Preparation of Fe-BEA zeolites by isomorphous substitution for oxidehydration of glycerol to acrylic acid

The preparation by post-synthesis isomorphous substitution of Fe_X-BEA-Y in one step was investigated for the oxidehydration of pure glycerol. TPR and DR UV–vis highlighted the presence of Fe^(+ III) species in the framework of zeolites. Iron allows the activation of the catalyst by the reduction by glycerol of part of Fe^(+ III) into Fe^(+ II) species, which stabilizes the glycerol conversion. Total glycerol conversion is obtained with 4 wt% of iron and acrylic acid yield reaches 23% over this catalyst. The Fe^(+ III) tetrahedral species are thought to be the main active redox sites for the formation of acrylic acid.     

Texturing of 3Y-TZP zirconia by electrophoretic deposition in a high magnetic field of 17.4 T

Ceramics can be textured during colloidal processing by aligning the suspended particles in a strong magnetic field and retaining this alignment in the green body. Attempts to align tetragonal zirconia particles however were not successful, not even in 12 T magnetic fields. In the current work, monoclinic zirconia was successfully aligned with its (1 0 0) plane perpendicular to the magnetic field direction by electrophoretic deposition (EPD) in a 17.4 T field. Moreover, textured tetragonal zirconia was developed by reactive sintering of undoped pure monoclinic zirconia and co-precipitated 8 mol% yttria-stabilized zirconia. The sintered tetragonal zirconia inherited the alignment of the monoclinic zirconia particle precursor and aligned with its (0 0 1) plane perpendicular to the magnetic field direction. The toughness of the (0 0 1)-oriented 3Y-TZP along the [0 0 1] direction of the textured zirconia was 65% higher than normal to it and 48% higher than the randomly oriented material.     

Novel method for synthesis of Fe core and C shell magnetic nanoparticles

Using a newly developed method, carbon-encapsulated iron (Fe) nanoparticles were synthesized by plasma due to ultrasonication in toluene. Fe core with carbon shell nanoparticles were characterized using Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM). Fe nanoparticles of diameter 7–115 nm are encapsulated by 7–8 nm thick carbon layers. There was no iron carbide formation observed between the Fe core and the carbon shell. The Fe nanoparticles have body centered cubic (bcc) crystal structure. Synthesized nanoparticles showed a saturation magnetization of 9 A m²/kg at room temperature. After thermal treatment crystalline order of the nanoparticles improved and saturation magnetization increased to 24 A m²/kg. We foresee that the carbon-encapsulated Fe nanoparticles are biologically friendly and could have potential applications in Magnetic Resonance Imaging (MRI) and photothermal cancer therapy.     

The effect of the surface nanostructure and composition on the antiwear properties of zirconia–titania coatings

This study describes the preparation, surface imaging and tribological properties of titania coatings modified by zirconia nanoparticles agglomerated in the form of island-like structures on the titania surface. Titania coatings and titania coatings with embedded zirconia nanoparticles were prepared by the sol–gel spin coating process on silicon wafers. After deposition the coatings were heat-treated at 500 °C or 1000 °C. The natural tendency of nanoparticles to form agglomerates was used to build separated island-like structures unevenly distributed over the titania surface having the size of 1.0–1.2 μm. Surface characterization of coatings before and after frictional tests was performed by atomic force microscopy (AFM) and optical microscopy. Zirconia nanoparticles were imaged with the use of transmission electron microscopy (TEM). The tribological properties were evaluated with the use of microtribometer operating in ambient air at technical dry friction conditions under normal load of 80 mN. It was found that nanocomposite coatings exhibit lower coefficient of friction (CoF) and considerably lower wear compared to titania coating without nanoparticles. The lowering of CoF is about 40% for coatings heated at 500 °C and 33% for the coatings heated at 1000 °C. For nanocomposites the wear stability was enhanced by a factor of 100 as compared to pure titania coatings. We claim that enhanced tribological properties are closely related to the reduction of the real contact area, lowering of the adhesive forces in frictional contacts and increasing of the composite hardness. The changes in materials composition in frictional contact has secondary effect.     

Preparation and UV-shielding property of Zr0.7Ce0.3O2–kaolinite nanocomposites

Nanocomposites of Zr_0.7Ce_0.3O₂–kaolinite were prepared by two different methods. The first method was by solid mixing of kaolinite and Zr_0.7Ce_0.3O₂ (ZrCeO), the latter being prepared by a citric acid complexion method, using an agate pestle and mortar as the mixing medium. The second method was by adding kaolinite during the synthesis of Zr_0.7Ce_0.3O₂ (ZrCeO) itself. Kaolinite was obtained by the elutriation of tin tailing, which was then exfoliated by planetary ball milling with 40 mass% of urea for 1–5 h. The resulting nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), and specific surface area (SSA) determination using the BET (Brunauer–Emmett–Teller) method. The characterization results proved that kaolinite was successfully exfoliated by urea treatment after 5 h. It was also found that ZrCeO–exfoliated kaolinite nanocomposite, synthesized by the citric acid complexion method, without adding NH₃, showed the highest UV-shielding property of > 80% absorption ability for wavelength < 400 nm. This is better than pure ZrCeO, even at the lower content of ZrCeO in the nanocomposite (i.e. at 70 mass% content).     

Iron-doped TiO2 nanotubes with high photocatalytic activity under visible light synthesized by an ultrasonic-assisted sol-hydrothermal method

A series of iron-doped anatase TiO₂ nanotubes (Fe/TiO₂ NTs) catalysts with iron concentrations ranging from 0.88 to 7.00 wt% were prepared by an ultrasonic-assisted sol-hydrothermal process. The structures and the properties of the fabricated Fe/TiO₂ NTs were characterized in detail and photocatalytic activity was examined using a reactive brilliant red X-3B aqueous solution as pollutant under visible light. The lengths of the NTs were determined to range from 20 nm to 100 nm. The incorporation of the iron ions (Fe³⁺) into the TiO₂ nanotubes shifted the photon absorbing zone from the ultraviolet (UV) to the visible wavelengths, reducing the band gap energy from 3.2 to 2.75 eV. The photocatalytic activity of the Fe/TiO₂ NTs was 2–4 times higher than the values measured for the pure TiO₂ nanotubes.     

Methane decomposition over ceria modified iron catalysts

The catalytic behaviour of ceria supported iron catalysts (Fe–CeO₂) was investigated for methane decomposition. The Fe–CeO₂ catalysts were found to be more active than catalysts based on iron alone. A catalyst composed of 60 wt.% Fe₂O₃ and 40 wt.% CeO₂ gave optimal catalytic activity, and the highest iron metal surface area. The well-dispersed Fe state helped to maintain the active surface area for the reaction. Methane conversion increased when the reaction temperature was increased from 600 to 650 °C. Continuous formation of trace amounts of carbon monoxide was observed during the reaction due to the oxidation of carbonaceous species by high mobility lattice oxygen in the solid solution formed within the catalyst. This could minimise catalyst deactivation caused by carbon deposits and maintain catalyst activity over a longer period of time. The catalyst also produced filamentous carbon that helped to extend the catalyst life.