Titanium Catalyst Research Articles

Titanium-Catalyzed Intermolecular Hydroaminoalkylation of Terminal Alkynes

AbstractTerminal alkynes undergo intermolecular hydroaminoalkylation reactions with secondary amines in the presence of titanium catalysts and depending on the catalyst and the structure of the substrates, allylic amines and/or imines are formed as products in moderate yields. In addition, the desired allylamines can also be obtained from a convenient reaction sequence consisting of an initial hydroaminoalkylation of trimethylsilyl-protected alkynes and a subsequent protodesilylation that selectively delivers γ-unsubstituted allylamines.

Visible-Light-Mediated TiO2-Catalyzed Aerobic Dehydrogenation of N-Heterocycles in Batch and Flow.

We report a simple and environmentally friendly method for synthesizing N-containing heterocycles via a visible-light-mediated aerobic dehydrogenation reaction. Using a nontoxic, stable, and inexpensive titanium dioxide catalyst, a variety of substituted quinoline, indole, quinoxaline, and 3,4-dihydroisoquinoline derivatives could be synthesized using the green oxidant molecular oxygen. Improved reactivity and scalability of this reaction were demonstrated by adapting the photochemical multiphasic reaction to a continuous flow system. To gain insight into the mechanism, we also conducted several mechanistic studies, including absorption analysis, light on-off testing, and NMR analysis. Especially, oxygen is reduced to hydrogen peroxide, and dimethyl sulfoxide is a critical scavenger of the oxidant byproduct for ensuring high yields.

Biodiesel production from Sisymbrium irio as a potential novel biomass waste feedstock using homemade titania catalyst

Biomass waste streams are a possible feedstock for a range of eco-friendly products and a crucial alternative energy source for achieving carbon neutrality; therefore, the efficient management of biomass waste has taken on a greater significance in recent years. Due to its well-comparable physic-chemical properties with fossil diesel, biodiesel is a potential substitute for fossil fuel. This study aimed to synthesize biodiesel from the widely available non-edible seed oil of Sisymbrium irio L. (a member of the Brassicaceae family) via a transesterification procedure over a homemade TiO2 catalyst. At 1:16 oil to methanol ratio, 93% biodiesel yield was obtained over 20 mg catalyst at 60 °C and 60 min. The ASTM methods were used to analyze the fuel properties. The quantitative and qualitative analysis was performed by FT-IR, GC-MS, and NMR spectroscopy. GC-MS study confirms 16 different types of fatty acids of methyl esters. FT-IR analysis showed important peaks that confirm the successful occurrence of biodiesel. 1H-NMR and 13C-NMR showed important peaks for converting triglycerides into corresponding FAMEs. The acid value (0.42 mg KOH/mg/kg), flash point (106 °C), and water content (0.034) of biodiesel are below the specified limit of ASTM D6751 whereas kinetic viscosity (3.72 mm2/s), density (0.874 kg/L), cloud point (− 4.3 °C) and pour point (− 9.6 °C) and high heating value (41.62 MJ/kg) fall within the specified range of ASTM D6751 test limit. The Unsaturation degree and oxidative stability of biodiesel are above ASTM D6751 test limit. The physic-chemical properties of the SIB confirm that it is eco-friendly fuel and a competitive source for manufacturing biodiesel on a commercial scale. Furthermore, the SIB is engine friendly and has good fuel efficacy.

Titania Nanoparticle Catalysed N‐Alkylation of Amines by Hydrogen Auto‐Transfer Mechanisms

AbstractUnlike well‐defined homogenous metal complex catalysts, no distinct heterogeneous catalysts are available for hydrogen auto‐transfer or borrowing hydrogen methodologies. Alternatively, a variety of noble metals, base metals, and bimetallic systems supported on various metal oxides are scrutinized for this purpose, mainly by modulating the ability of metals and supports in a multistep reaction. Herein, we demonstrate that pristine defect‐induced titania nanoparticle catalyst is an efficient and recyclable heterogeneous catalyst for the preparation of N‐alkylated products (>90 %) in the absence of expensive hydrogen source, costly ligands, additives, or costly metals under greener conditions. Furthermore, the nano‐sized titania catalyst tolerates functional groups with high yields. In addition, the ‐alkylation of aniline affords the corresponding alkylated products in d yields with long aliphatic alcohols. Finally, the results of the control tests show that a process of Hydrogen Auto transfer is responsible for carrying out the reaction.

The titania-catalyzed oxidative dehydrogenation of methanol to formaldehyde

Formaldehyde is one of the most important intermediates in today’s chemical industry and mainly produced via the silver or Formox process. In this study, we introduce titania as a new catalyst for the oxidative dehydrogenation (ODH) of methanol to formaldehyde. Bulk titania catalysts were tested under methanol ODH conditions and the influence of reaction temperature, residence time and feed composition was investigated. The highest formaldehyde yield exhibited in the titania-catalyzed methanol ODH was around 70 % at 600 °C, 1.6 gCatalyst h molMethanol−1 and 2.0 molMethanol molOxygen−1. Long-term experiments were performed to get insights on the catalyst stability. While catalyst deactivation was observed at 600 °C (90–60 % methanol conversion after 72 h) and 550 °C (90–85 % methanol conversion after 72 h), methanol conversion (85 %) was stable and no deactivation occurred at 500 °C. Characterization of the used catalysts by nitrogen physisorption, powder X-ray diffraction and thermogravimetric analysis revealed deposition of carbon species as the main cause of catalyst deactivation. By alternating reaction and regeneration with oxygen, constant methanol conversions (90 %) and formaldehyde yields (70 %) were achieved at 600 °C.

Promotion of B(C6F5)3 as Ligand for Titanium (or Vanadium) Catalysts in the Copolymerization of Ethylene and 1-Hexene: A Computational Study.

Density functional theory (DFT) is employed to investigate the promotion of B(C6F5)3 as a ligand for titanium (or vanadium) catalysts in ethylene/1-hexene copolymerization reactions. The results reveal that (I) Ethylene insertion into TiB (with B(C6F5)3 as a ligand ) is preferred over TiH, both thermodynamically and kinetically. (II) In TiH and TiB catalysts, the 2,1 insertion reaction (TiH21 and TiB21) is the primary pathway for 1-hexene insertion. Furthermore, the 1-hexene insertion reaction for TiB21 is favored over TiH21 and is easier to perform. Consequently, the entire ethylene and 1-hexene insertion reaction proceeds smoothly using the TiB catalyst to yield the final product. (III) Analogous to the Ti catalyst case, VB (with B(C6F5)3 as a ligand) is preferred over VH for the entire ethylene/1-hexene copolymerization reaction. Moreover, VB exhibits higher reaction activity than TiB, thus agreeing with experimental results. Additionally, the electron localization function and global reactivity index analysis indicate that titanium (or vanadium) catalysts with B(C6F5)3 as a ligand exhibit higher reactivity. Investigating the promotion of B(C6F5)3 as a ligand for titanium (or vanadium) catalysts in ethylene/1-hexene copolymerization reactions will aid in designing novel catalysts and lead to more cost-effective polymerization production methods.

The Advantages of Double Catalytic Layers for Carbon Nanotube Growth at Low Temperatures (<400 °C) in 3D Stacking and Power Applications

A double catalytic layer scheme is proposed and investigated for the low temperature growth of carbon nanotubes (CNTs) over Co (Cobalt), Al (Aluminum), and Ti (Titanium) catalysts on a silicon substrate. In this work, we demonstrate the growth of CNTs by a thermal chemical vapor deposition (TCVD) process at both 350 °C and 400 °C. Based on scanning electron microscopy (SEM) and Raman spectroscopy analyses, the good quality of the CNTs is demonstrated. This study contributes to the on-going research on integrating semiconductors into packaging and power-related applications, as demonstrated with the low resistance (~128 Ω) and high thermal conductivity (~29.8 Wm−1 K−1) of our developed CNTs.

Comparison of Eco-friendly Ti-M Bimetallic Coordination Catalysts and Commercial Monometallic Sb- or Ti-Based Catalysts for the Synthesis of Poly(ethylene-co-isosorbide terephthalate).

Sustainable development greatly benefits from the effective synthesis of bio-based copolymers that are environmentally friendly. To enhance the polymerization reactivity for the production of poly(ethylene-co-isosorbide terephthalate) (PEIT), five highly active Ti-M (M = Mg, Zn, Al, Fe, and Cu) bimetallic coordination catalysts were designed. The catalytic activity of Ti-M bimetallic coordination catalysts and single Sb- or Ti-based catalysts was compared, and the effects of catalysts with a different type of coordination metal (Mg, Zn, Al, Fe, and Cu) on the thermodynamic and crystallization properties of copolyesters were explored. In polymerization, it was found that Ti-M bimetallic catalysts with 5 ppm (Ti) had higher catalytic activity than traditional antimony-based catalysts or Ti-based catalysts with 200 ppm (Sb) or 5 ppm (Ti). The Ti-Al coordination catalyst showed the best-improved reaction rate of isosorbide among the five transition metals used. Utilizing Ti-M bimetallic catalysts, a high-quality PEIT was successfully synthesized with the highest number-average molecular weight of 2.82 × 104 g/mol and the narrowest molecular weight distribution index of 1.43. The glass-transition temperature of PEIT reached 88.3 °C, allowing the copolyesters to be used in applications requiring a higher Tg, like hot filling. The crystallization kinetics of copolyesters prepared by some Ti-M catalysts was faster than that of copolyesters prepared by conventional titanium catalysts.

Reductive Deoxygenative Functionalization of Alcohols by First‐Row Transition Metal Catalysis

Comprehensive SummaryAlcohols are among the most accessible functionalities. Catalytic deoxygenative functionalization of alcohols is highly synthetically appealing. While significant progress has been made on the reactions with nucleophiles, the reactions with electrophilic coupling partners remain a real challenge. This manuscript highlights the advance in this direction, which is mainly achieved by the first‐row transition metals. The low‐valent titanium catalyst has shown the unique reactivity to homolytically cleave the C—OH bonds. The formed carbon radicals could either undergo reduction to give protonation products or couple with carbon fragments to form C—C bonds. This chemistry is initially realized using a stoichiometric amount of titanium reagents and later extended to catalytic variants. Nickel features a variety of oxidation states ranging from Ni0 to NiIV, and both two‐electron oxidative addition and single‐electron process are involved in their activation of an electrophile. These properties enable nickel to catalyze reductive C—C coupling of alcohols with R–X electrophiles. The reaction is first reported on the reactions of allylic alcohols, then extended to benzylic alcohols and, very recently non‐activated alcohols. Recent effort has resulted in many invaluable methodologies that highly improve the reaction efficiency for the construction of aliphatic C—C bonds. The use of cobalt and copper catalysts not only expands the substrate scope of these reactions but also shows the new reactivity and selectivity issues.

Defects Tune the Strong Metal-Support Interactions in Copper Supported on Defected Titanium Dioxide Catalysts for CO2 Reduction.

A highly active and stable Cu-based catalyst for CO2 to CO conversion was demonstrated by creating a strong metal-support interaction (SMSI) between Cu active sites and the TiO2-coated dendritic fibrous nano-silica (DFNS/TiO2) support. The DFNS/TiO2-Cu10 catalyst showed excellent catalytic performance with a CO productivity of 5350 mmol g-1 h-1 (i.e., 53,506 mmol gCu-1 h-1), surpassing that of almost all copper-based thermal catalysts, with 99.8% selectivity toward CO. Even after 200 h of reaction, the catalyst remained active. Moderate initial agglomeration and high dispersion of nanoparticles (NPs) due to SMSI made the catalysts stable. Electron energy loss spectroscopy confirmed the strong interactions between copper NPs and the TiO2 surface, supported by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy. The H2-temperature programmed reduction (TPR) study showed α, β, and γ H2-TPR signals, further confirming the presence of SMSI between Cu and TiO2. In situ Raman and UV-vis diffuse reflectance spectroscopy studies provided insights into the role of oxygen vacancies and Ti3+ centers, which were produced by hydrogen, then consumed by CO2, and then again regenerated by hydrogen. These continuous defect generation-regeneration processes during the progress of the reaction allowed long-term high catalytic activity and stability. The in situ studies and oxygen storage complete capacity indicated the key role of oxygen vacancies during catalysis. The in situ time-resolved Fourier transform infrared study provided an understanding of the formation of various reaction intermediates and their conversion to products with reaction time. Based on these observations, we have proposed a CO2 reduction mechanism, which follows a redox pathway assisted by hydrogen.

Well-dispersed titanium dioxide and silver nanoparticles on external and internal surfaces of asymmetric alumina hollow fibers for enhanced chromium (VI) photoreductions

Heterogenous photocatalysis is a suitable alternative for wastewater treatment. The supporting of the solid catalyst in a porous material is suggested to facilitate catalyst recovery and reuse. Here we propose for the first time the evaluation of supporting silver (Ag)-decorated titanium dioxide (TiO2) catalysts on internal and external surfaces of alumina hollow fibers with asymmetric pore size distribution. The produced catalysts were considered for Cr(VI) photoreductions. The ultrasound-assisted process potentialized the distribution of Ag nanoparticles on the TiO2 surface. The loading of Ag nanoparticles at concentrations greater than 5 wt% was necessary to improve the TiO2 activity for Cr(VI) photoreduction. The loading of Ag nanoparticles at 30 wt% improved the Cr(VI) photoreduction of the single TiO2 catalyst from 40.49 ± 0.98 to 55.00 ± 0.83% after 180min of reaction. Suspended and supported Ag-decorated TiO2 catalysts achieved total Cr(VI) photoreduction after 21h of reaction. The adjusted reaction rate constant with the externally supported Ag-TiO2 catalyst was 3.57 × 10-3 ± 0.18 × 10-3min-1. Similar reaction rate constants were achieved with suspended and internally supported catalysts (approximately 2.70 × 10-3min-1). After 10 sequential reuses, all catalysts presented similar Cr(VI) photoreductions of approximately 66%. Nevertheless, the use of the externally supported catalyst is suggested for Cr(VI) photoreductions due to its superior catalyst activity at least in the first reuse cycles.

Effect of yttrium on catalytic performance of Y-doped TiO2 catalysts for propane dehydrogenation

Defective bulk catalysts based on TiO2 have superior catalytic performance for propane dehydrogenation (PDH). The oxygen vacancy concentration and the number of active sites on the catalyst surface can be effectively tuned by doping metal in TiO2. Herein, yttrium (Y)-doped titanium dioxide (nY/TiOx) catalysts were in-situ synthesized via the coprecipitation method to study the effect of rare earth metal Y doping on the structure of TiO2 and the catalytic performance for PDH. Experimental results demonstrate that Y-doped TiO2 exhibits higher catalytic activity, propylene selectivity and stability than bare TiO2. Full characterizations with X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy of pyridine adsorption (Py-IR), temperature-programmed desorption of ammonia (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), and Raman techniques on these catalysts reveal that Y3+ can enter TiO2 lattice, and the lattice stability of the catalyst can be enhanced by replacing Ti4+ to form Y–O–Ti structure. Meanwhile, the introduction of an appropriate amount of Y can obviously promote the PDH reaction by adjusting the acidity of the catalyst, improving the release capacity of TiO2 lattice oxygen and increasing the formation of active centers. Nevertheless, excessive Y doping will lead to pore clogging, and the exposure of active sites will be reduced, resulting in the degradation of catalytic performance.

Floating immobilized TiO2 catalyst for the solar photocatalytic treatment of micro-pollutants within the secondary effluent of wastewater treatment plants

Floating immobilized spherical titanium dioxide catalysts were used to degrade micro-pollutants by solar photocatalysis. The degradation of the micro-pollutants was performed in the secondary effluent of a wastewater treatment plant. During the experimental period, the continuous measurement of the solar ultraviolet (UV) radiation intensity was performed. The micro-pollutants were degraded to an average of 55% after 9 h of irradiation. A substance-specific degradation affinity was found, whereby degradation rates varied by a factor of up to 3.5. The substance-specific adsorption behavior was identified as a major limitation of the reaction performance. With an increasing influence of adsorption limitation, the degradation kinetics changed from the pseudo-first order to pseudo-zero order. A correlation between degradation rate and solar irradiance could only be found for substances with high degradation/adsorption affinity. For diclofenac, a 95% degradation rate could be achieved at a radiation dose of approximately 190 mWh/m². The investigated technology represents a promising possibility for a minimally invasive extension of wastewater treatment plants. Possibilities of implication were estimated and discussed within this work, whereby possibilities arise for large-scale as well as decentral treatment plants.

CH3COOH.TiO2: An excellent catalyst for the green nitration of toluene by N2O4

The solvent-free nitration of toluene with N2O4 gas over solid acid catalysts is a green reaction for preparing the mono-nitrotoluene (NT) isomers. The acid-modified catalysts are more efficient than common catalysts for this type of reaction. For this purpose, a titanium dioxide (TiO2) catalyst is synthesized with a sol-gel method and modified by acetic acid to increase catalytic properties. The acid-modified TiO2 (CH3COOH·TiO2) is characterized by different analyses. To optimization of toluene nitration conditions, reaction temperature (X1) (30 < X1 < 60 °C), N2O4/toluene molar ratio (X2) (0.5 < X2 < 2), and the amount of catalyst (X3) (0.05 < X3 < 0.3 g) factors were investigated by Minitab software with the CCD-RSM. Three responses including the selectivity of meta-NT isomer (Sm), the ratio of para-NT to ortho-NT selectivity (Sp/o), and the selectivity of by-products (Sbp) were considered for the optimization. Statistical parameters were applied to evaluate the goodness of fitting for the models. Optimum values for X1, X2, and X3 parameters are 57.9 °C, 1.91, and 0.25 g, respectively. The conversion of toluene under these conditions is 93.2%. The comparison of Sm, Sp/o, and Sbp in CH3COOH.TiO2 (1.51%, 0.8, and 5.48%, respectively) with Fe2O3 (8.5%, 0.43, and 20.57%, respectively), SiO2 (8.43%, 0.48, and 16.24%, respectively), TiO2 (5.9%, 0.57, and 13.87%, respectively), TiO2–Fe2O3 (4.72%, 0.64, and 9.18%, respectively), and TiO2–SiO2 (4.42%, 0.67, and 5.73%, respectively) catalysts show that this catalyst has a low Sm and Sbp as well as a higher Sp/o than other mentioned catalysts. The mechanism of the mentioned reaction is reviewed in the presence of CH3COOH·TiO2 catalyst. The high stability of the CH3COOH·TiO2 is proved by the reusability test, and it is found that its stability against inactivation is more than the TiO2 catalyst.

2-hydroxyethylammoniumsulfate ionic liquid performance as simultaneous fuel and sulfating agent in tablet-like manganese and iron incorporated titania synthesis: Biodiesel production from waste oil

The efficient tablet-like manganese and iron incorporated titania catalyst was synthesized in the presence of 2-hydroxyethylammonium sulfate (ILS) as both fuel and sulfating agent via microwave for biodiesel production. Catalyst characterizations were conducted by XRD, FESEM, EDX, BET-BJH, and TPD-NH3 analyses. The catalyst was also synthesized via other fuels including urea, 2-hydroxyethylammonium acetate (ILA), and 2-hydroxyethylammonium formate (ILF). The nature of fuels affected the catalyst’s physicochemical properties and performance. Urea created a large portion of wide pores in the catalyst. ILS led to the creation of a highly acidic catalyst with an acid density of 0.804 mmol/m2. Oleic acid conversion for catalysts synthesized by urea, ILA, ILF, and ILS in the condition of 110 °C, 1.5 h, 9 wt% catalyst, alcohol to oil mole ratio of 20 was 63.5, 39.36, 48.56, and 93.11 %. MnFeTi(ILS) showed a good capability for producing biodiesel from sunflower (92.12 %) and waste oil (91.43 %). The catalyst was reused 5 times, and only a 6 % conversion loss was detected.

Synthesis of camphene by α-pinene isomerization using acid nano titanium dioxide catalysts

In this study, we investigated the application of an acidic titanium dioxide catalyst in fixed bed reactors for the isomerization of α-pinenes.

Fully tuneable ethylene-propylene elastomers using a supported permethylindenyl-phenoxy (PHENI*) catalyst.

Using a highly active supported permethylindenyl-phenoxy (PHENI*) titanium catalyst, high molecular weight ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomers are prepared using slurry-phase catalysis. Final copolymer composition was found to reflect the monomer feed ratio in a linear fashion, to access a continuum of material properties with a single catalyst. Post-polymerisation crosslinking of EPDM was also demonstrated in a model sulfur vulcanisation system.

Photochemical conversion of nitrate to ammonium ions by a newly developed photo-reductive titanium dioxide catalyst: implications on nitrogen recovery

Global nitrate contamination in source water poses a threat to both natural ecosystems and public health. Application of diethylene glycol (DEG) ligand-doped titanium dioxide nanoparticles serves to photo-reductively convert nitrate to ammonium.

Synergetic role of copper-modified phosphotungstic acid supported on titania catalysts for the conversion of bio-glycerol to glycerol carbonate

An efficent heterogeneous bi-functional Cu-tuned phostotunstic acid reusable catalyst is developed for the selctive carbonylation of biomass-derived glycerol for boosted stable activity and higher selectivity of glycerol carbonate.

Reductive Umpolung and Defunctionalization Reactions through Higher-Order Titanium(III) Catalysis

AbstractThe single-electron transfer from an in situ formed titanium(III) catalyst to ketones, imines, nitriles, Michael acceptors, and many other functions has enabled a large number of intra- and intermolecular reductive umpolung reactions. Likewise, it allows the homolytic cleavage of functional groups for selective defunctionalizations. These reactions often take place with the participation of two titanium(III) species, avoiding free-radical pathways and enabling high catalyst control of the reaction selectivity. This account discusses the development of the individual reactions together with the fundamental mechanistic discoveries that led to a better understanding of such titanium(III)-catalyzed processes in general.1 Introduction2 Active Titanium(III) Species and Additives3 Ketone-Nitrile Couplings4 Further Reductive Umpolung Reactions5 Catalytic Homolytic C–CN and C–SO2R Cleavage6 Conclusion