Titanium Catalyst Research Articles

Facile synthesis of a nano titanium catalyst and its performance in selective oxidation of aromatic and pyridinic alcohols under visible light

The oxidation of alcohols to the corresponding carbonyl compounds is of great significance in chemical synthesis and fine chemical production.

Highly efficient and stable ordered mesoporous Ti-Al composite oxide catalyst for oxidative dehydrogenation of ethylbenzene to styrene with CO2

Ordered mesoporous Ti-Al composite oxides (OMTA-x) with variable Al/Ti atomic ratios have been prepared by a facile approach, and were evaluated as catalysts for oxidative dehydrogenation of ethylbenzene to styrene with CO2 (CO2-ODEB). Compared to Al2O3-supported titania catalyst, the resultant catalysts OMTA-x displayed inspiringly improved catalytic performance. For example, catalyst OMTA-2 demonstrated notable activity up to 20 h with maximum styrene yield of 69.4%, even after five times regeneration by calcination. The superior catalytic performance of OMTA-x can be attributed to the highly homogenous dispersion of Ti, the obviously improved surface acidity and redox properties, and the excellent textural and structural properties. The bridging oxygen in the surface Ti4+OAl3+ bonds with enhanced reactivity with H were concluded as the critical active sites for dehydrogenation of ethylbenzene, and new understanding for the development of TiO2-based catalysts with superior catalytic activity, stability, and reusability for CO2-ODEB was provided.

Synthesis of Thin Titania Coatings onto the Inner Surface of Quartz Tubes and Their Photoactivity in Decomposition of Methylene Blue and Rhodamine B

An evaporation-deposition coating method for coating the inner surface of long (>1 m) quartz tubes of small diameter has been studied by the introduction of two-phase (gas-liquid) flow with the gas core flowing in the middle and a thin liquid film of synthesis sol flowing near the hot tube wall. The operational window for the deposition of continuous titania coatings has been obtained. The temperature range for the deposition of continuous titania coatings is limited to 105–120 °C and the gas flow rate is limited to the range of 0.4–1.0 L min−1. The liquid flow rate in the annular flow regime allows to control the coating thickness between 3 and 10 micron and the coating porosity between 10% and 20%. By increasing the liquid flow rate, the coating porosity can be substantially reduced. The coatings were characterized by X-ray diffraction, N2 chemisorption, thermogravimetric analysis, and scanning electron microscopy. The coatings were tested in the photocatalytic decomposition of methylene blue and rhodamine B under UV-light and their activity was similar to that of a commercial P25 titania catalyst.

Photocatalytic ozonation in an immersion rotary body reactor for the removal of micro-pollutants from the effluent of wastewater treatment plants

Abstract Carrier-bound titanium dioxide catalysts were used in a photocatalytic ozonation reactor for the degradation of micro-pollutants in real wastewater. A photocatalytic immersion rotary body reactor with a 36-cm disk diameter was used, and was irradiated using UV-A light-emitting diodes. The rotating disks were covered with catalysts based on stainless steel grids coated with titanium dioxide. The dosing of ozone was carried out through the liquid phase via an external enrichment and a supply system transverse to the flow direction. The influence of irradiation power and ozone dose on the degradation rate for photocatalytic ozonation was investigated. In addition, the performance of the individual processes photocatalysis and ozonation were studied. The degradation kinetics of the parent compounds were determined using liquid chromatography tandem mass spectrometry. First-order kinetics were determined for photocatalysis and photocatalytic ozonation. A maximum reaction rate of the reactor was determined, which could be achieved by both photocatalysis and photocatalytic ozonation. At a dosage of 0.4 mg /mg DOC, the maximum reaction rate could be achieved using 75% of the irradiation power used for sole photocatalysis, allowing increases in the energetic efficiency of photocatalytic wastewater treatment processes. The process of photocatalytic ozonation is suitable to remove a wide spectrum of micro-pollutants from wastewater.

Hydrothermal catalysis of waste greases into green gasoline, jet, and diesel biofuels in continuous flow supercritical water

AbstractThe production of green gasoline, jet, and diesel biofuels from waste greases was achieved using a novel hydrothermal, continuous‐flow catalytic process operating under supercritical water conditions, with recycled water the only added chemical. Thermally and chemically stable catalysts were explored to optimize yields of liquid biofuels and to minimize production of gases and acidic compounds. A 50:50 mixture of brown and yellow waste greases converted into 76.6 wt% liquid biocrude (BC); the remainder converted to water and gases. Less than 0.2% of the feedstock (FS) formed carbon char (mainly amongst catalyst particles). Various tubular reactors (Inconel, Hastelloy, titanium, stainless) showed no interior defects, erosion, or mass loss after runs. The titanium catalyst was fully recovered and regenerated back to its original potency. The BC was further refined into 28%, 48%, 20%, and 4 wt%, respectively for green gasoline, jet, diesel, and bunker. Biofuels were analyzed for compound class compositions and reaction mechanisms were proposed. Hundreds of identified fuel products (C3‐C35) from processing oleic acid as a pure model compound were identified. The neat green gasoline and diesel biofuels, along with a 50% green jet blend (with petroleum Jet A), were tested in appropriate spark ignition, turbine, and diesel engines at the University of Minnesota Engine Labs. The biofuels achieved 107.7%, 97.2%, and 101.3% engine power performance levels relative to petroleum fuels (91‐Octane, Jet A, #2 Diesel) along with lower CO and pollutant emissions. The biofuels complied with American Society for Testing and Materials (ASTM) fuel specifications (D4814, D7566, D975) including mandated corrosion and low sulfur limits of all three biofuels. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Enhanced stability of Ti-containing silica catalysts for biodiesel epoxidation with hydrogen peroxide: Presence of strong metal–support interactions for alleviating permanent deactivation

The deactivation of titanium catalysts supported by well-ordered silica (SBA-15) and amorphous fumed silica synthesized by incipient wetness impregnation (IWI) and wet impregnation (WI) was comparatively investigated during epoxidation of methyl oleate with H2O2 at 50 °C. The formation of oxygen vacancies during epoxidation resulted in the loss of active species, leading to permanent catalyst deactivation. The WI-based catalysts exhibited superior stability to that of the IWI-based equivalents. Moreover, the use of SBA-15 as a support enabled higher stability than that of SiO2. The permanent deactivation rates for the 4Ti/SiO2-IWI, 4Ti/SBA-15-IWI, 4Ti/SiO2-WI, and 4Ti/SBA-15-WI catalysts were approximately 44.0%, 32.6%, 8.1%, and 0%, respectively. Various catalyst characterization data revealed that the configuration featuring stable surface Ti was present in the 4Ti/SBA-15-WI catalyst with strong metal–support interactions. This was attributed to the strong Ti4+ tetrahedral coordination achieved through Si–O–Ti bonds, the low degree of reducibility of the Ti catalyst, and the high dispersion and small particle size of Ti. Consequently, this modified surface can mitigate permanent catalyst deactivation caused by the surface oxygen vacancies.

Recycling of Waste V2O5–WO3/TiO2 Catalysts in the Iron Ore Sintering Process Via a Preballing Approach

Extensive use of selective catalytic reduction denitrogenation technology leads to the generation of a large amount of hazardous waste vanadium–tungsten–titanium catalysts. To valorize these waste ...

Hydroxylation of Arylboronic Acids to Phenols on a Vanadia–Titania Catalyst

Hydroxylation of Arylboronic Acids to Phenols on a Vanadia–Titania Catalyst

Ethylene/Myrcene Copolymers as New Bio-Based Elastomers Prepared by Coordination Polymerization Using Titanium Catalysts

The synthesis of ethylene/myrcene copolymers was performed using half-titanocene catalysts in the presence of a methylaluminoxane (MAO) cocatalyst. Cyclopentadienyl-phenoxide catalysts, Cp*TiCl2(O-...

Determination of photocatalytic properties of supported catalysts with low-cost NOx sensors and the Arduino platform

Carrier-bound titanium dioxide catalysts were used for the photocatalytic conversion of nitrogen dioxide. In this context, inexpensive metal oxide sensors were tested for their usefulness in the investigation and characterization of the photocatalysts. UV-A light emitting diodes of wavelength 365 nm stimulated the catalysts. By dimming the light emitting diodes, the influence of the energy flux density on the conversion kinetics could be investigated. The observed conversation followed first-order kinetics. The light intensity has shown a large influence at lower irradiances. At high irradiances an increase in recombination effects can be assumed, which makes irradiances greater than 40 W/m2 inefficient. From that point on no significant increase in the rate of conversation could be measured. The photon efficiency at low irradiances was determined to be 4.55% decreasing to 0.59% at higher irradiances. The flow rate of gas passing through the catalysts appears to have a linear effect on the overall rate of conversion. This is evidenced by a constant half-life within the reactor in relation to variable flow rate. The sensors have been shown to be calibratable and sufficiently stable, which raises the possibility of using the sensors for spatially resolved measurements within reaction systems.

Influence of Hydrogen Pressure on the Structure of Platinum–Titania Catalysts

Dependent on the application or characterization method catalysts are exposed to different gas pressures, which results in different structures. The quantitative determination of the structure and composition of a catalyst as a function of its gas environment allows the establishment of structure–performance relationships. Herein, we determine the structure of a platinum–titania catalyst under hydrogen during temperature-programmed reduction over 3 orders of magnitude in pressure, from 1 to 950 mbar. The pressure significantly influences the hydrogen uptake kinetics and the consecutive structural transformations of the platinum–titania catalyst. The reduction of the platinum precursor becomes pressure-independent above 30 mbar. Yet, the related spillover and stability of adsorbed hydrogen on the titania are a function of pressure. Higher pressures promote higher hydrogen uptake and prevent desorption of hydrogen from the catalyst. The hydrogen uptake triggers a phase transformation of anatase to rutile which is, as a result, pressure dependent. The presented systematic approach establishes a pressure–structure relation which can be applied for the catalyst treatment and to frame existing results on the catalytic system. Treating the same material at two different pressures will lead to different structures.

Selective tandem catalysis for the synthesis of 5-hydroxymethylfurfural from glucose over in-situ phosphated titania catalysts: Insights into structure, bi-functionality and performance in flow microreactors

5-Hydroxymethylfurfural (HMF) synthesis from glucose over in-situ phosphated titania catalysts is presented. Phosphates were incorporated into titania framework forming a titanium phosphate surface layer, where the coordinatively unsaturated tetrahedral TiO4 units act as water-tolerant Lewis acid site (LAS) and the adjacent protonated phosphate as Brønsted acid site (BAS), together forming Lewis-Brønsted acid pairs at molecular-level proximity. Glucose turnover and HMF selectivity were enhanced due to the rapid fructose transfer from LAS to the adjacent BAS for its dehydration to HMF, facilitating LAS liberation for another glucose turnover. Reactions in a water-2-methyltetrahydrofuran biphasic system in packed-bed microreactors gave 66% HMF yield (from 1 M glucose at 150 °C), where the HMF space time yield is about two orders of magnitude higher than that in batch and the literature work. Phosphate leaching from the catalyst is rather limited, whereas the catalyst deactivated mainly by humin deposition and could be regenerated by calcination.

Partial oxidation of isobutylene using Ni TiOx

We report an aerobic partial oxidation of isobutylene into isoprene, acetone, and para-xylene using a mesoporous Ni TiOx catalytic material. In this work, two catalysts were found to synthesize two of these three valuable products with high selectivity, with p-xylene being synthesized with a selectivity of 46.0% and isoprene being synthesized with a selectivity of 64.7%, with overall conversions of isobutylene being 34.0% and 11.9% respectively. These reactions were done at relatively low temperatures (300 °C or below) and are conducted at flow rates of 10 sccm oxygen and isobutylene. The nickel titania catalysts were studied extensively using various characterization methodologies such as TEM, Raman, XRD, and XRF.

Investigation on influence of manganese nanoparticles loading in electrochemical activity of anatase titania catalysts and its role in photocatalytic performance

Investigation on influence of manganese nanoparticles loading in electrochemical activity of anatase titania catalysts and its role in photocatalytic performance

Liquid-phase sulfur recovery within a eutectic solvent coupled with low temperature carbon disulfide hydrolysis

Liquid phase sulfur recovery was explored in a eutectic solvent to demonstrate proof-of-concept for an alternative Claus tail gas cleanup process. A simulated tail gas feed containing 3% H2S and 1.5% SO2 was converted to elemental sulfur within a biphenyl and diphenyl ether eutectic solvent. The formed sulfur accumulates at the bottom of the reactor upon solvent saturation, allowing for liquid–liquid separation if the temperature is maintained above 120 °C. Alternatively, crystallization of elemental sulfur could be performed with lower sulfur solubility in the solvent at room temperature. In the temperature range of 120 – 150 °C, a Claus equilibrium conversion of > 99% was achieved when care was taken to maintain the H2S/SO2 ratio at 2:1. While lower temperature favours Claus equilibrium, destruction of other sulfur containing species such as CS2 often suffers at these lower temperatures. Therefore, CS2 destruction was explored within the eutectic solvent over both alumina and titania catalysts, which are commonly used in commercial applications. Good conversions were observed for both alumina and titania when maintaining the H2S/SO2 ratio at 2:1. Better CS2 conversions of 95% (over alumina) and 98% (over titania) were observed at 150 °C when operating at an H2S/SO2 ratio at 2.3:1. The total sulfur conversions, when assuming theoretical equilibrium conversion in the sulfur recovery unit, combined with the liquid-phase tail gas cleanup process ranged from 99.3 to 99.9%. Addition of water to the feed negatively affected the CS2 destruction on titania but had little effect on alumina. At sulfur saturation conditions, CS2 destruction was not affected on titania, but was negatively affected on alumina at 150 °C.

Highly conductive titania supported iridium oxide nanoparticles with low overall iridium density as OER catalyst for large-scale PEM electrolysis

To enable future large-scale generation of hydrogen via proton exchange membrane (PEM) electrolysis, utilization of scarce iridium-based catalysts required for the oxygen evolution reaction (OER) has to be significantly lowered. To address this question, the facile synthesis of a highly active TiO2 supported iridium oxide based OER catalyst with reduced noble metal content and an Ir-density of the catalyst powder as low as 0.05–0.08 gIr cm-3 is described in this work. A high surface area corrosion-resistant titania catalyst support homogeneously coated with a 1-2 nm thin layer of amorphous IrOOHx is oxidized in molten NaNO3 between 350-375°C. This procedure allows for a controllable phase transformation and crystallization to form a layer of interconnected IrO2 nanoparticles of ≈2 nm on the surface of the TiO2 support. The increase in crystallinity is thereby accompanied by a significant increase in conductivity of up to 11 S cm-1 for a 30 wt% Ir loaded catalyst. Oxidized samples further display a significantly increased stability with less detectable Ir dissolution under OER conditions. With a mass-based activity of 59 A g-1 at an overpotential of 300 mV, the electrocatalytic activity is maintained at the level of the highly active amorphous IrOOHx phase used as precursor and outperforms it at higher current densities through the increased conductivity. MEA measurements with catalyst loadings of 0.2-0.3 mg cm-2 further confirm the high catalytic activity and initial stability at industrially relevant current densities. The introduced synthesis approach therefore shows a path for the fabrication of novel highly active and atom-efficient oxide supported catalysts with complex nanostructures and thin homogenous nanoparticle coatings that allows a future large-scale application of PEM electrolysis technology without restrictions by the natural abundance of iridium.

Bulk defect-dependent initial steps of acetone oxidation on rutile TiO2(110)

Systematic model investigations revealed that defects, particularly bulk Ti3+ interstitials, play a crucial role in directing reactions of alcohols and aldehydes at rutile Titania (TiO2), a cheap, nontoxic and earth abundant catalyst. Coadsorption with oxygen may enhance the population of certain reaction paths. As systematic studies on the reactivity of ketones are rare, we studied the interaction of acetone with slightly (∼5%) and highly (∼20%) reduced rutile TiO2(110) surfaces by Temperature Programmed Desorption (TPD) and polarised Fourier-Transform Infrared Reflexion Absorption Spectroscopy (FT-IRRAS) to elucidate surface intermediates and reaction products. For low defect densities the only reaction observed occurs at high temperatures resulting in the formation of propane and propene of less than 1%. At high Ti3+ defect densities a stabilisation of acetone on the surface by the formation of a diolate was observed. In the presence of oxygen, the partial formation of a tilted acetone species is apparent in FT-IRRAS. A concomitant activation of the CH-bond can be attributed to the interaction with Oad atoms and can relate to thermally induced low temperature decomposition to water and carbon dioxide. However, in contrast to alcohols and aldehydes, both intermediates do not react to other more valuable products.

KINETIC HETEROGENEITY OF POLYMER PRODUCTS OBTAINED IN THE PRESENCE OF MICROHETEROGENIC CATALYTIC SYSTEMS BASED ON GEL CHROMATOGRAMS

Background: the polymer product obtained in the presence of microheterogeneous catalytic systems is characterized by fairly molecular weight distribution (MWD), resulted from kinetically nonequivalent active centers (ACs) in the system that initiate the polymerization process. The nature and composition of ACs are determined by setting and solving an inverse problem on the formation of MWD. This problem is acute because revealing the nature of the kinetic heterogeneity explains changes in the molecular and consumer parameters of the product for different catalyst compositions and propagation modes in polymerizations. Aim: This study aimed to develop methods and algorithms for interpreting gel chromatograms to analyze the kinetic heterogeneity of a polymer product obtained industrially in microheterogeneous catalytic systems. Methods: the solution method is based on the assumption that the formed MWD is a superposition of distributions inherent in each type of ACs. Since the problem in the final formulation refers to the Fredholm integral equations of the first kind, the regularization method of A. N. Tikhonov is used for its numerical solution, with the original problem being preliminary discretized. This methodology and the developed software algorithms were used to determine the kinetic heterogeneity of titanium- and neodymium-containing catalytic systems. Results and discussion: The MWD analysis revealed two types of ACs with an average molecular weight of ATi-lnM = 11.3 and BTi-lnM = 13.2 in the titanium catalyst and three types of ACs ANd-lnM = 11.1, BNd-lnM = 12.7 and CNd-lnM = 14 for the neodymium catalyst, respectively. Conclusions: repeated computational experiments under different polymerization conditions and requirements for the preparation of a catalytic system make it possible to reveal a relationship with the resulting heterogeneity of ACs. It allows us to set and solve problems of controlling the molecular characteristics of the resulting polymer product.

Influence of Anatase-Rutile Ratio on Band Edge Position and Defect States of TiO2 Homojunction Catalyst

Removal of toxic air and water dissociation in the environment has become a major challenging issue throughout the world. Mixed phase rutile-anatase titanium dioxide catalysts are very effective in photocatalysis and have been studied extensively. However, the mechanism causing this effect and band alignment of the two phases are not fully understood. Pointing to the issue, we have designed one-dimensional mixed-phase TiO2 and introduced defects near the valence band. Experimental results showed that band alignment between two phases, up-shift of the band edge, and optimum anatase percentage play a key role in the enhancement of the photocatalytic activity. We predicted shifts in band edge originating from surface electric dipole layer induced by defects.

Trans-1,4-polybutadiene: Influences of Lewis bases on polymerization of butadiene with supported titanium catalyst systems

Three MgCl2 supported TiCl4 pro-catalysts; Cat-A, Cat-B and Cat-C were synthesized. Cat-A was synthesized without any internal Lewis base (ILB); while Cat-B and Cat-C were synthesized using diisobutyl phthalate and ethyl benzoate as ILBs respectively. The effect of ILBs on stereoregularity and the microstructure of polybutadiene (PBD) was investigated. The vast differences in the amount of trans-1,4-structure of PBD by Cat-A, Cat-B and Cat-C systems were correlated with the nature of ILBs used by studying their polymerization kinetics. The energy barriers for polymerization reactions were calculated for all three catalysts systems using Arrhenius equation. Cat-B, has shown the highest energy barrier (23 kJ/mol) due to DIBP as ILB in its structure. Cat-A has given the lowest trans-1,4-PBD as it does not contain any ILB and has the minimum energy barrier (12 kJ/mol) while Cat-C has shown medium energy barrier (17 kJ/mol). We have also studied the effect of suitable external Lewis bases during polymerization. The effect of polymerization parameters like Al/Ti molar ratio, Al/LB molar ratios and the temperatures on PBD microstructure were studied. Based on the polymerization kinetics studies and the effect of LBs on PBD microstructure, a possible reaction mechanism has been proposed.