Ti Mixed Oxide Research Articles

Improvement in the hydrodesulfurization of dibenzothiophene over supported NiMoW catalysts

Various supported NiMoW sulfided catalysts were synthetized and tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The influence of cetyl trimethyl ammonium bromide (CTAB) on the properties of titania, silica and Si–Ti mixed oxide, prepared by sol–gel and used as supports, was evaluated. The active metals were then sequentially co-impregnated on the carrier. For all catalysts, the Ni/[Ni(MoW)] and Mo/W atomic ratios were kept constant and equal to 0.5 and 1, respectively. In addition, the total metal content was 18 wt% for each sample. All catalysts were characterized by BET, TEM, XRD and UV–Vis. The use of CTAB as a surfactant influences the textural properties of the supports. Among the studied samples, the best catalyst was NiMoW/Si–Ti, which showed a DBT conversion of 94% after 5 h of reaction at 320 °C and 5.3 MPa. For comparison, a commercial NiMo/Al2O3 catalyst was used as a reference.

Effect of low-temperature underwater plasma produced of new properties of Mo–Ti mixed oxide composites for electron transport layer in the dye-sensitized solar cells

TiO2-based composites are potential materials for dye solar cells. Here we report a new method for synthesizing a new composite material based on molybdenum and titanium oxides. Low-temperature underwater direct current plasma is used as a synthesis method, and Mo and Ti wires were as electrodes. The polarity of the electrode affects the nature of the array. It was found that with the positive polarity of the molybdenum electrode (anode), MoO3 decorated with rutile is formed. The mixed-phase TiO2 decorated MoOx (x = 2.75–2.85) is formed by the negative polarity Mo of the electrode (cathode). The synthesized composites show improved characteristics in the photocurrent response and photovoltaics.

Photocatalytic Degradation of Mixed Dyes in Aqueous Phase by MgAlTi and ZnAlTi Mixed Oxides

This study reported the synthesis and evaluation of mixed metal oxides MgO/Al2O3–TiO2 and ZnO/Al2O3–TiO2 as heterogeneous photocatalysts for the potential degradation of a mixture of organic dyes such as methylene blue and methyl orange. First, hydrotalcites were synthesized by two different methods (conventional and microwave); then they were treated at 500 °C to obtain the corresponding Mg/Al–Ti and Zn/Al–Ti mixed metal oxides. The Layered Double Hydroxide (LDH) and the Mixed Metal Oxides were characterized by N2 adsorption–desorption, X-ray Diffraction, Fourier transform infrared, X-Ray photoelectron Spectrometry and Scanning Electron Microscopy. The degradation processes of the dyes were carried out under ultraviolet light irradiation and absorbance readings were compared using a UV–vis spectrometer. The ensuing degradation of products was corroborated through a mass spectrometry analysis. According to the photodegradation efficiency of dyes under UV irradiation, the activity of the samples showed the following order: ZnAlTiM > ZnAlTiC > MgAlTiC > MgAlTiM. The improvement in the activity of ZnAlTiM may be attributed to its lowest reflectance and highest degree of UV light absorbance, its smallest valence band and its ZnO-support interaction. Degradations of 25% and 68% were achieved for methyl orange and methylene blue, respectively, after 120 min of reaction. The degradation process conforms to the Langmuir–Hinshelwood type kinetic model.

Highly Selective Catalytic Dechlorination of Dichloromethane to Chloromethane over Al−Ti Mixed Oxide Catalysts

AbstractIn this paper, a series of Al−Ti mixed oxides with different Al/Ti ratios are prepared by a simple sol‐gel method and they are used as active catalysts for selective dechlorination of dichloromethane to chloromethane. The Al−Ti mixed oxide catalyst with the same molar ratio of Al and Ti shows the highest activity in dechlorination of dichloromethane. The strong and abundant Lewis acid sites in the Al−Ti mixed oxides formed along with Al−O−Ti bondings are responsible for the high catalytic activity toward the selective dechlorination reaction in this work. From a kinetic study, the activation energy of this reaction over the optimum Al−Ti mixed oxide catalyst appears to be 59.4 kJ mol−1 based on Langmuir‐Hinshelwood model. The improved catalytic performance suggests that the Al−Ti mixed oxide could be used as the effective catalyst for the highly selective dechlorination of dichloromethane to chloromethane.

A novel single-step hydrogenation of 2-imidazolecarboxaldehyde to 2-methylimidazole over Pd-impregnated Al–Ti mixed oxide and kinetics

A novel and clean route for the hydrogenation of 2-imidazolecarboxaldehyde to 2-methylimidazole with high yield and selectivity over a Pd/ATMO catalyst.

Nitrogen oxides reduction by liquid petroleum gas over Co–Ce–Ti catalysts in a simulated rotary reactor

Hydrocarbons could be used as the reductant for elimination of NOx emissions. Liquid petroleum gas, with higher carbon hydrocarbons and cheaper costs, may be of practical value as reducing agents. Due to the consumption of hydrocarbons by oxygen, the NOx reduction efficiency is significantly inhibited by oxygen in the flue gas. In this research, a novel rotary reactor, realizing the alternating cycle of adsorption zone and reduction zone, was proposed to overcome this negative effect. Co–Ce–Ti mixed oxide catalysts synthesized by a sol–gel method were tested in a simulated rotary reactor for NOx removal by liquid petroleum gas and characterized by SEM, BET, XRD and XPS. The results showed that catalysts exhibited better NO conversion efficiency at higher temperature but were highly susceptible to oxygen. Catalysts achieved nearly full removal of NOx from flue gas at 300 °C in a simulated rotary reactor, and 300 °C is considered to be the most optimum temperature with lower energy consumption and excellent flue gas purification performance.

Comparative study on transition element doped Mn–Zr–Ti-oxides catalysts for the low-temperature selective catalytic reduction of NO with NH3

The effect of Cu, Fe, Co, Ni, Cr and Zn on Mn–Zr–Ti mixed oxides catalysts introduced by co-precipitation was investigated. The Mn–Co catalyst showed the highest NO conversion near 100% and a good N2 selectivity > 90% at 200–300 °C. Comparing with the Mn–non catalyst, the Mn–Co catalyst presented a higher reaction rate constant at 120 °C with 23.3 ml s−1 g−1. The Mn–Co catalyst possesses a high concentration of Mn4+ and surface labile oxygen, which should improve the redox property and increase catalytic activity. Additionally, the Mn–Co showed the highest ratio of Lewis acid sites. The resistance to SO2 was improved by incorporation of Co. In summary, the Mn–Zr–Ti mixed oxides catalyst have a better N2 selectivity than other Mn-based catalysts and could be improved by doping with Co.

Enhanced selective catalytic reduction of NO with NH3 via porous micro-spherical aggregates of Mn–Ce–Fe–Ti mixed oxide nanoparticles

We rationally designed a high performance denitration (De-NOx) catalyst based on a micrometer-sized spherical Mn–Ce–Fe–Ti (CP-SD) catalyst for selective catalytic reduction (SCR). This was prepared by a co-precipitation and spray drying (CP-SD) method. The catalyst was systematically characterized, and its morphological structure and surface properties were identified. Compare with conventional Mn–Ce–Fe–Ti (CP) catalysts, the Mn–Ce–Fe–Ti (CP-SD) catalyst had superior surface-adsorbed oxygen leading to enhanced “fast NH3-SCR” reaction. The as-obtained Mn–Ce–Fe–Ti (CP-SD) catalyst offered excellent NO conversion and N2 selectivity of 100.0% and 84.8% at 250 °C, respectively, with a gas hourly space velocity (GHSV) of 40,000 h−1. The porous micro-spherical structure provides a larger surface area and more active sites to adsorb and activate the reaction gases. In addition, the uniform distribution and strong interaction of manganese, iron, cerium, and titanium oxide species improved H2O and SO2 resistance. The results showed that the Mn–Ce–Fe–Ti (CP-SD) catalyst could be used prospectively as a denitration (De-NOx) catalyst.

Selective catalytic reduction of NOx with NH3 over Mn–Zr–Ti mixed oxide catalysts

Mixed oxide catalysts yMn–Zr–Ti (y/10/10 with y = 1, 3, 5, 7 and 9) for the selective catalytic reduction (SCR) of NOx with NH3 in the presence of oxygen were synthesized by co-precipitation. The catalyst 5Mn–Zr–Ti exhibited a catalytic activity higher than 87% above 160 °C and N2 selectivity above 92% at 100–300 °C. The SCR performance was quite stable at 180 and 200 °C for 15 h. Mn species are shown to improve the catalytic activity by providing more surface labile oxygen, while a synergistic effect among Mn, Zr and Ti species suppressed the generation of N2O. According to in situ DRIFT analysis, NOx was primarily reduced by the reaction of bidentate nitrate and monodentate nitrito species with adsorbed NH3. Subsequently, a comprehensive reaction mechanism was proposed. Accordingly, the formation of NH species was inhibited, and hence, the N2O formation by the reaction of NH and bidentate nitrate was suppressed. Furthermore, the investigation of the deactivation mechanism by SO2 indicated that both the deposition of ammonium sulfates and the sulfation of Mn active sites resulted in the deactivation of the catalyst 5Mn–Zr–Ti. The deposition of ammonium sulfates at 180 °C was more pronounced than that at 220 °C.

TOC and COD removal from instant coffee and coffee products production wastewater by chemical coagulation assisted electrooxidation

This paper describes and discusses an investigation into the treatment performance of Boron-Doped Diamond (BDD), Pt coated Ti (Pt) and various Mixed Metal Oxide (MMO) anodes after pre-treatment chemical coagulation for total organic carbon (TOC) and chemical oxygen demand (COD) removal from instant coffee and coffee products production wastewater. Firstly, the performance of coagulants, AlCl3, Al2(SO4)3, FeCl3 and FeSO4 were investigated. Secondly, the treatment performance of BDD, Pt and various MMO anodes, the influence of the applied current density and the effect of flow rate for the best-performed electrode were investigated. Also, specific energy consumptions and anode performances were calculated and evaluated for electrooxidation process. At the pre-treatment, among the four coagulants, AlCl3 showed the best performance removing 29% TOC and COD 55%. At the electrooxidation process, BDD electrode achieved the best performance. At the end of the 6 h run period, BDD electrode achieved 95% TOC and 97% COD removal. On the other hand, Pt and MMO electrodes just removed 13–22% TOC and 25–50% COD respectively. In this study, the BDD electrode performed much better than Pt and MMO electrodes.

Efficient removal of bisphenol A from wastewaters: Catalytic wet air oxidation with Pt catalysts supported on Ce and Ce–Ti mixed oxides

Catalytic wet air oxidation (CWAO) of an aqueous solution of bisphenol A (BPA) was investigated at 160 ℃ and 2.0 MPa of air in a batch reactor. Activity of supported platinum catalysts (2.5 wt%), prepared by wet impregnation, was compared with pure cerium and cerium–titanium oxide catalysts. Supported platinum catalysts showed higher activities in the removal of BPA than pure CeO2, Ce0.8Ti0.2O2 and Ce0.2Ti0.8O2. The oxidation reaction was followed the pseudo-first order rate law and the highest BPA removal, 97% and 95%, was achieved with Pt/CeO2 and Pt/Ce0.8Ti0.2O2 catalysts respectively. The CWAO of BPA aqueous solution was not a surface area specific reaction but the more important factor affecting the activity of studied catalysts was the amount of chemisorbed oxygen of these samples.

W-Modified Mn–Ti Mixed Oxide Catalyst for the Selective Catalytic Reduction of NO with NH3

A W-modified Mn–Ti mixed oxide catalyst was prepared by the homogeneous precipitation method, which was applied to the selective catalytic reduction of NO with NH3 (NH3-SCR). The introduction of W could broaden the operation temperature window of Mn0.5TiOx, and the Mn0.5W0.1TiOx showed good SCR activity at 150–350 °C (NOx conversion above 80%). The results of characterization demonstrated that W introduction improved the redox ability, inhibited the separated NO/NH3 oxidation abilities, and provided additional Brønsted and Lewis acid sites. When W was added, less NO oxidation to NO2 possibly led to the inhibition of SCR activity at low temperatures, while the increase of NH3 adsorption and inhibition of NH3 oxidation could contribute to the enhancement of high-temperature SCR activity. Meanwhile, the N2O formation in the NH3-SCR over both Mn0.5TiOx and Mn0.5W0.1TiOx mainly follow the Eley–Rideal mechanism, and the introduction of W inhibited the N2O formation.

Activity and characterization of Ce–Mo–Ti mixed oxide catalysts prepared by a homogeneous precipitation method for selective catalytic reduction of NO with NH 3

Abstract A series of Ce–Mo–Ti mixed oxide catalysts prepared by a homogeneous precipitation method were evaluated for selective catalytic reduction (SCR) of NO with NH3. These catalysts were characterized by BET, XRD, XPS, SEM, TEM and H2-TPR. The experimental results indicated that the optimal Ce–Mo–Ti mixed oxide catalyst (Ce40Mo10Ti) exhibited excellent SCR activity in a wide temperature range of 250–450 °C as well as strong resistance to high gas hourly space velocity, 10% H2O or/and 1000 ppm SO2. The introduction of Mo could enhance redox property and increase the amount of Ce3+, accompanied by the increment of oxygen vacancies and adsorbed oxygen species on the catalyst surface, which were advantageous to the SCR reaction over Ce–Mo–Ti oxide catalyst. In addition, good dispersion of Ce and Mo species on TiO2 and their synergetic interaction also contributed to its remarkable NH3–SCR performance.

Hydrogen production by crude glycerol steam reforming over Ni–La–Ti mixed oxide catalysts

The production of H2-rich gaseous mixtures from steam reforming of crude glycerol was investigated on ternary Ni–La–Ti catalysts. Ni–La–Ti mixed oxides containing 15 wt% of Ni and a La/Ti atomic ratio of 1 were prepared by a coprecipitation method and characterized by a variety of physical and spectroscopic techniques. Samples were calcined in air at 700 °C or 850 °C for 2 h. Ni–La–Ti samples calcined at 700 °C (NiLaTi700) showed a well-defined NiO phase and an amorphous La–Ti mixed oxide, while those calcined at 850 °C (NiLaTi850), exhibited two well defined phases of NiO and LaTiO3 perovskite, respectively. NiO was completely reduced to metallic Ni on both solids under pure H2 at 650 °C and the resulting Ni0 phase remained as a separate phase under the steam reforming conditions. Standard catalytic tests for the steam reforming of glycerol were performed at 500 °C or 650 °C by feeding the fixed-bed tubular reactor with a crude glycerol:water solution containing 30 wt% glycerol. The best results were achieved on NiLaTi700 at 650 °C, obtaining H2 yields and H2/CO2 molar ratios close to the theoretical values predicted by the steam reforming reaction stoichiometry. A slight activity decay was observed on NiLaTi700 with the progress of the reaction, probably reflecting the formation of small amounts of coke.

Supported metal sulfates on Ce–TiOx as catalysts for NH3–SCR of NO: High resistances to SO2 and potassium

Cu and Fe sulfates were loaded on a Ce–Ti mixed oxide and tested for the reduction of NO with NH3. The loading of metal sulfate greatly enhances the resistance to SO2 of the Ce–Ti oxide. The prepared catalysts also show better performances after doping with K2O if compared to the V–W–TiOx catalyst. Surface characterizations reveal that better resistance to potassium oxide can be attributed to better acidity and reducibility. The catalyst with iron sulfate supported on Ce–TiOx was found to be a promising catalyst for NO removal in the flue gas with high alkali metal content.

Enhanced photo-degradation of bisphenol a under simulated solar light irradiation by Zn–Ti mixed metal oxides loaded on graphene from aqueous media

In the present study, the mixed metal oxides (rGO-ZnTi-MMO-x, x presents weight percentage of GO) were obtained by thermal treatment of a Zn–Ti layered double hydroxides-graphene oxide (GO-ZnTi-LDHs) composite.

Effect of W–Ti target composition on the surface chemistry and electronic structure of WO3–TiO2 films made by reactive sputtering

Tungsten–titanium (W–Ti) mixed oxide thin films were fabricated using reactive sputtering of W–Ti alloy targets with Ti content ranging from 0 to 30wt%. The effect of target composition on film structure, surface/interface chemistry and chemical valence state of the W and Ti cations was investigated in detail. All films were amorphous in nature as confirmed by X-ray diffraction analyses. For growth times of 1h, the thicknesses of the W–Ti–O films decreased significantly from 150 to 35nm with increasing Ti content in the target, confirming that the oxide film growth behavior is dependent on the sputter-target composition. The chemistry and composition of the films probed using X-ray photoelectron spectroscopy (XPS) confirms the existence of W and Ti in their highest oxidation states of 6+ and 4+, respectively. Quantification of binding energy shifts for W and Ti core-level transitions confirms the formation of WO3–TiO2 composite oxide films. Depth profiles confirm and validate film uniformity, as well as film thickness differences and variable oxidation behavior of W and Ti in the films.

Surface Ba species effective for photoassisted NOx storage over Ba-modified TiO2 photocatalysts

Surface modification of a TiO2 photocatalyst with Ba species was investigated in photoassisted nitrogen oxide (NOx) storage under UV-light irradiation. The NOx storage capacity in the Ba-modified TiO2 photocatalyst was 1.4 times higher than that of the non-modified TiO2 photocatalyst. Structure and role of the surface Ba species on a TiO2 surface were characterized using temperature programmed reaction (TPR), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). The characterization results suggested that Ba–Ti mixed oxides with a two-dimensional layer and amorphous structure on a TiO2 surface were generated via decomposition of Ba(NO3)2 precursors by O2 pretreatment at 773K. Based on the results of the characterizations and the reactions, the generated Ba–Ti mixed oxides on a TiO2 surface stored NOx more densely than the TiO2 surface; therefore, the generation improved the activity in the photoassisted NOx storage under UV-light irradiation.

The selective catalytic reduction of NO with NH3 over a novel Ce–Sn–Ti mixed oxides catalyst: Promotional effect of SnO2

A series of novel catalysts (CexSny) for the selective catalytic reduction of NO by NH3 were prepared by the inverse co-precipitation method. The aim of this novel design was to improve the NO removal efficiency of CeTi by the introduction of SnO2. It was found that the Ce–Sn–Ti catalyst was much more active than Ce–Ti and the best Ce:Sn molar ratio was 2:1. Ce2Sn1 possessed a satisfied NO removal efficiency at low temperature (160–280°C), while over 90% NO removal efficiency maintained in the temperature range of 280–400°C at the gas hourly space velocity (GHSV) of 50,000h−1. Besides, Ce2Sn1 kept a stable NO removal efficiency within a wide range of GHSV and a long period of reacting time. Meanwhile, Ce2Sn1 exhibited remarkable resistance to both respectively and simultaneously H2O and SO2 poisoning due to the introduction of SnO2. The promotional effect of SnO2 was studied by N2 adsorption–desorption, X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR) for detail information. The characterization results revealed that the excellent catalytic performance of Ce2Sn1 was associated with the higher specific surface area, larger pore volume and poorer crystallization. Besides, the introduction of SnO2 could result in not only greater conversion of Ce4+ to Ce3+ but also the increase amount of chemisorbed oxygen, which are beneficial to improve the SCR activity. More importantly, a novel peak appearing at lower temperatures through the new redox equilibrium of 2Ce4++Sn2+↔2Ce3++Sn4+ and higher total H2 consumption can be obtained by the addition of SnO2. Finally, the possible reaction mechanism of the selective catalytic reduction over Ce2Sn1 was also proposed.

Activity and characterization of a Ce–W–Ti oxide catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A Ce–W–Ti mixed oxide catalyst prepared by a single step sol–gel method exhibited excellent SCR activity and high resistance to H2O and SO2. The excellent catalytic performance might be attributed to the improved dispersion of Ce species on TiO2, the increase in the amount of Ce3+ and chemisorbed oxygen and the strong interaction among ceria, tungsten and titania owing to the addition of WO3.