Ti Catalyst Research Articles

Recycling of Poly(L-Lactic acid) based 3D Printed Objects Using Sn, Ti and Triazabicyclodecene-Based Catalysts in Film Or Microfiber Form

Recycling of Poly(L-Lactic acid) based 3D Printed Objects Using Sn, Ti and Triazabicyclodecene-Based Catalysts in Film Or Microfiber Form

Designing of imine thiophene-ligated metal-complexes and implication in ethylene polymerization

Polyethylene is the single largest volume polymer produced globally using Ziegler-type catalysts. Numerous modifications have been reported in search of a better catalyst that can control molecular weight, polydispersity, and branching. In our attempts to identify a suitable imine thiophene-ligated chromium complex, we examined 9 different titanium complexes computationally. The DFT investigations considered barriers for insertion, propagation, and termination by β-H elimination or chain transfer, and identified N-(4-methoxyphenyl)-2-phenyl-1-(thiophen-2-yl)ethan-1-imine(L9) as the most suitable ligand. Subsequently, L9 was prepared in good yield (70%) by condensing 2-phenyl-1-(thiophen-2-yl)ethan-1-one with 4-methoxyaniline. Ligand L9 was treated with early transition metal precursors (Ti, Cr, Zr) to generate a homogenous catalyst. The identity of these catalysts was unambiguously ascertained using a combination of NMR, ICP, FT-IR, UV-Vis spectroscopy, and ESI-MS. The performance of L9-ligated titanium complex [Cat.1] was examined in ethylene polymerization using MMAO as a co-catalyst. Insertion of ethylene was tracked using high-pressure NMR experiments and Cat.1 was found to be active in the polymerization. Ethylene polymerization conditions were optimized to obtain high activity and molecular weight polyethylene. The chromium complex [Cat.2] outperformed the Ti and Zr-derived catalysts with the highest TOF of 6294 mol of PE/mol of Cr/h. Cat.2 produced high molecular weight, high-density polyethylene.

The Role of L‐Ligands in Silica‐Supported Ti Oxo/Imido Heterometathesis Catalysts

ABSTRACTWe report here the preparation and characterization of new well‐defined silica‐supported Ti imido complexes that present an L‐ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron‐donating 4‐(N,N‐dimethylamino)pyridine (2s) or bidentate 2,2′‐bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid‐state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L‐ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development.

A Green and Efficient Electrocatalytic Route for the Highly‐Selective Oxidation of C–H Bonds in Aromatics over 1D Co3O4‐Based Nanoarrays

Electrocatalytic oxidation of C‐H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value‐added chemicals. Herein, a highly selective and continuous‐flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4‐based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D‐Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with selectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm‐2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, and continuous‐flow process for precise control over production selectivity of value‐added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90 % at a toluene conversion of 47.6 % using 1D Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1 % at a conversion of 32.1 % after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained with a selectivity of 92 % at a conversion of 58.5 % at high current density (>1.5 mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable, efficient, and continuous-flow process for precise control over the production selectivity of value-added oxygenated derivatives in the electrochemical oxidation of aromatic hydrocarbons.

Rational design of titanium-doped Y zeolite for hydrodenitrogenation of aromatic N-heterocyclic compounds

Ti modified Y zeolites with different Ti content were synthesized by in-situ hydrothermal crystallization method and used as the support of hydrodenitrogenation (HDN) catalyst. The forms of Ti species in the zeolites and the effect of Ti incorporation on the active metal states of the corresponding catalysts were investigated by XRD, UV–Vis DRS, XPS, HAADF-STEM, ICP-OES, Py-FTIR, H2-TPR, HRTEM, and DFT calculation. The results show that the incorporation of in-situ Ti species into Y zeolite led to a decrease in the Brønsted acid sites (BAS) /Lewis acid sites (LAS) value of the corresponding catalyst, but effectively enhanced the stacking layer number of the WS2 active phase by weakening the interaction between the active metals and the supports, which is manifested in the improvement of the hydrogenolysis activity and the decrease of the hydrogenation activity of the catalyst. When the hydrogenolysis activity and hydrogenation activity in the catalyst match to a certain extent, that is, the BAS/LAS value and the stacking layer number of the active phase reach an appropriate value, the HDN catalyst exhibited the highest catalytic activity. The NiW/Y-0.1Ti catalyst with suitable amount of BAS and stacking layer number of active phase showed the maximum kHDN values (11.7 × 10-4 mol·g−1·h−1 and 3.9 × 10-4 mol·g−1·h−1) and TOFs (1.91 h−1 and 1.04 h−1) of quinoline and indole HDN.

Conversion of limonene to limonene diol over activated carbon supported Ti catalyst

AbstractA series of activated carbon supported Ti-3,3′-ethylen bis(3,4-dihydro-2H-1,3-benzoxazine) complex catalysts (denoted Ti-Bz (0.25)/AC, Ti-Bz(0.37)/AC, and Ti-Bz (0.5)/AC) was evaluated in the conversion of limonene to limonene diol using H2O2 as oxidant. The opening of oxazine ring as a step to the titanium complex formation was highlighted, as far as we are aware, for the first time, by NMR analysis. A range of characterization methods, including SEM–EDS, nitrogen physisorption, ATR-FTIR, and XRD, showed that the procedure used in the preparation of these materials was reproducible. Parameters affecting the catalytic performances in the production of limonene diol, such as reaction temperature, amount of catalyst tested, and its catalytic stability, were studied. Ti-Bz (0.5)/AC was the most performant catalyst leading to limonene diol yield of 36.7%. The recyclability of the catalyst was evaluated along three catalytic consecutive tests that showed no significant difference of performance compared with that of fresh catalyst.

Efficient synthesis of 1,6-Hexanediol via the hydrogenation of dimethyl adipate on CuZn nanoparticles with balanced Cu+-Cu0 sites

In this paper, Cu-based catalyst was prepared by co-precipitation method with DMA hydrogenation as a probe reaction. Compared to the binary Cu-ZnO catalyst, the Cu-ZnO-MxOy (M=Ce, Ti, Zr and Al) catalyst modified with the addition of a third component showed a significant increase in 1,6-Hexanediol (HDO) selectivity. Especially, the dimethyl adipate (DMA) conversion, HDO selectivity and yield of the CZZ catalyst were up to 75.7 %, 53.6 % and 40.6 %, respectively, higher than others. Combining the results of XPS and N2O titration, HDO selectivity was adjusted by varying the Cu+/(Cu0+Cu+) ratio via the third component. The addition of ZrO2 prevented further reduction of Cu+ due to the formation of Cu/ZrO2 or Cu/ZnO species, thus maintaining a constant Cu+/(Cu0+Cu+) ratio and realizing the efficient selectivity of HDO. Furthermore, higher alkaline site density on the CZZ catalyst facilitated CO bond activation further favored the formation of 1,6-hexanediol. In addition, CZZ catalyst had better hydrogen dissociation capacity and smaller catalyst particle size, which will further promote the hydrogen dissociation and thus the hydrogenation process of DMA.

Effect of Lactic Acid on the SCR Performance of Plate-type Ce-Mo /Ti Catalyst

Effect of Lactic Acid on the SCR Performance of Plate-type Ce-Mo /Ti Catalyst

Copolymerization of norbornene with 1-hexene catalyzed by sulfur-containing Schiff base titanium complex and density functional theory analysis

Sulfur-containing salicylaldimine ligand and corresponding titanium complex were synthesized and characterized this work, indicating structural conformity with the design. By using diethylaluminum chloride (EADC) as a cocatalyst, the titanium complex exhibited high activity (∼106 g·mol−1·h−1) in the copolymerization of norbornene (NB) and 1-hexene (1-C6), producing oligomer with a molecular weight of approximately 500. The catalytic copolymerization results were interpreted by combining experimental analysis and density functional theory (DFT). The results indicated that the insertion of norbornene and 1-hexene into Ti catalysts was thermodynamically feasible. Although the reaction barrier for norbornene monomer insertion into the metal active center was lower than that of 1-hexene, the strong steric hindrance between NBE monomer and NBE units in the oligomer chain hindered continuous NBE insertion. By comparing the reaction rates in equimolar systems, the initial insertion step of 1-hexene monomer into the Ti-Et structure was found to be much easier than norbornene insertion, resulting in a lower quantity of norbornene groups in the copolymerization product than 1-hexene groups.

Mechanism of the Sharpless Epoxidation Reaction: A DFT Study.

The Sharpless reaction is an enantioselective epoxidation of prochiral allylic alcohols that employs a Ti(IV) catalyst formed from titanium tetra(isopropoxide), Ti(O-i-Pr)4, diethyl tartrate (DET), and the oxidizing agent tert-butyl hydroperoxide. The M06-2X DFT functional with the 6-311+G(d,p) basis set has been employed to model the structures and energetics of the Sharpless epoxidation reaction. The monomeric tetracoordinate titanium(IV) diethyltartrate is thermodynamically strongly favored to dimerize, producing a pentacoordinate catalyst, [Ti(DET)(O-i-Pr)2]2, that is a more reactive chiral epoxidation catalyst. The rapid ligand exchange reactions needed to generate the "loaded" catalyst and to repeat the overall catalytic cycle have been examined and are found to have activation energies that are much lower than the epoxidation barriers. The transition structures and activation energies for the enantioselective epoxidation of allyl alcohol, trans-methyl-allyl alcohol and trans-tert-butyl-allyl alcohol with the "loaded" Sharpless catalyst, [Ti2(DET)2(O-i-Pr)2-(OAllyl)-(OOt-Bu)], are presented. The effect of the C═O···Ti interactions on the activation energies and the significance of the O-C-C═C dihedral angle on the enantioselectivity of the epoxidation reaction are discussed.

Ti(III)-Catalyzed Anti-Markovnikov Reduction of Epoxides with Borohydride.

We have developed a Ti catalyst that carries out the anti-Markovnikov reduction of a wide range of epoxides; [BH4]- is used as both the electron and the hydrogen atom source. It requires only mild conditions and accommodates a broad range of epoxide substrates. The Ti catalyst is readily available and is environmentally friendly.

Low-temperature methanation of fermentation gas with Ni-based catalysts in a multicomponent system

A large amount of greenhouse gases, such as carbon dioxide and methane, are released during the production process of bioethanol and biogas. Converting CO2 into methane is a promising way of capturing CO2 and generating high-value gas. At present, CO2 methanation technology is still in the early stage. It requires high temperature (300–400 ℃) and pressure (> 1 MPa), leading to high cost and energy consumption. In this study, a new catalyst, Ni–Fe/Al–Ti, was developed. Compared with the activity of the common Ni/Al2O3 catalyst, that of the new catalyst was increased by 1/3, and its activation temperature was reduced by 100℃. The selectivity of methane was increased to 99%. In the experiment using simulated fermentation gas, the catalyst showed good catalytic activity and durability at a low temperature and atmospheric pressure. Based on the characterization of catalysts and the study of reaction mechanisms, this article innovatively proposed a Ni–Fe/Al–Ti quaternary catalytic system. Catalytic process was realized through the synergism of Al–Ti composite support and Ni–Fe promotion. The oxygen vacancies on the surface of the composite carrier and the higher activity metals and alloys promoted by Fe accelerate the capture and reduction of CO2. Compared with the existing catalysts, the new Ni–Fe/Al–Ti catalyst can significantly improve the methanation efficiency and has great practical application potential.

Preparation of N-B doped composite electrode for iron-chromium redox flow battery

Iron-chromium redox flow battery (ICRFB) is an electrochemical energy storage technology that plays a vital role in dealing with the problems of discontinuity and instability of massive new energy generation and improving the acceptance capacity of the power grid. Carbon cloth electrode (CC) is the main site where the electrochemical reaction occurs, which always suffers from the disadvantages of poor electrochemical reactivity. A new N-B co-doped co-regulation Ti composite CC electrode (T-B-CC) is firstly generated and applied to ICRFB, where the REDOX reaction can be promoted significantly owing to the plentiful active sites generated on the modified electrode. As contrasted with ICRFB with normal CC electrode, after 50 battery charge/discharge cycles, the discharge capacity (1,990.3 ​mAh vs 1,155.8 ​mAh) and electrolyte utilization (61.88% vs 35.94%) of ICRFB with CC electrode (T-B-CC) are significantly improved. Furthermore, the energy efficiency (EE) is maintained at about 82.7% under 50 cycles, which is 9.3% higher than that of the pristine electrically assembled cells. The co-modulation of heteroatom doping and the introduction of Ti catalysts is a simple and easy method to improve the dynamics of the Cr3+/Cr2+ and Fe3+/Fe2+ reactions, enhancing the performance of ICRFBs.

Preparation and catalytic behaviors of an iron-based V–W–Ti catalyst: a novel strategy for low-temperature denitrification and synergistic toluene removal

Fe-doped vanadium tungsten titanium (V–W–Ti) catalysts were fabricated via an impregnation method.

Mechanism of ammonium bisulfate deposition on V1M5/Ti catalysts with synergistic effects of V and M (M = Ce, Co, Fe, and Mn) in low-temperature NH3-SCR

Two pathways of ammonium sulfate deposition on V1M5/Ti are elucidated in detail. The synergistic effect of V sites and transitional metal sites reflects in the selective adsorption and competitive oxidation of SO2.

Impact of catalyst support on water-assisted CO oxidation over PdO/MO2 (M = Sn, Ti, and Si) catalysts: experimental and theoretical investigation.

This study examines the impact of different supports, SnO2, TiO2, and SiO2, on the catalytic performance and water resistance of PdO-based catalysts for CO oxidation. By merging experimental data with DFT calculations, we reveal the distinct characteristics exhibited by each catalyst. Specifically, PdO/TiO2 stands out with exceptional CO oxidation activity, attributed to its minute Pd grain size, robust CO adsorption capacity, and optimal Pd dispersion on the TiO2 surface. In stark contrast, PdO/SnO2 demonstrates heightened activity in the presence of water vapor, whereas PdO/SiO2 experiences minimal effects, as evidenced by quantitative H2O-TPD analysis and DFT simulations of surface interactions. Water vapor exerts differential impacts on the catalytic performance of these catalysts by modulating the energy barriers associated with the CO oxidation mechanisms. On PdO/TiO2, the presence of H2O or H-OH elevates the energy barrier for CO to abstract surface oxygen, thereby diminishing catalyst activity under humid conditions and gradually leading to deactivation due to accumulated surface H2O and OH species. Conversely, on PdO/SnO2, when H2O is present in the form of OH, the energy barrier diminishes, augmenting CO oxidation activity owing to the beneficial effects of surface OH groups.

A facile strategy of “laser-direct-writing” to develop self-supported Ni30B70–Ti catalysts for boosted and durable alkaline oxygen evolution

A Ni30B70–Ti catalyst for seawater splitting was designed via ball milling and laser direct writing technology. The OER overpotential of Ni30B70–Ti was 370 mV at a current density of 50 mA cm−2, 260 mV lower than that of the commercial Ni mesh.

Effect of surface modification on silica supported Ti catalysts for cyclohexene oxidation with vapor-phase hydrogen peroxide.

Surface modification via grafting of organic moieties on a Lewis acid catalyst (silica supported Ti catalyst, Ti-SiO2) alters the activation of H2O2 in vapor-phase cyclohexene epoxidation. Grafting a fluorous group (1H,1H-perfluoro-octyl) suppresses activity of Ti-SiO2. Conversely, grafting either a nonpolar group (octyl) or a polar aprotic group (triethylene glycol monomethyl ether) enhances rates and shifts selectivity toward trans-1,2-cyclohexanediol.

Simultaneously accomplishing selective catalytic reduction of NO and catalytic oxidation of CO in a catalyst coupling system

Considering that nitrogen oxides (NOx) and carbon monoxide (CO) usually meantime exist in industrial flue gas, it is meaningful to develop a collaborative control technology for the simultaneous purification of NOx and CO. In this work, the catalysts xCu-1V-5W/Ti were evaluated in the simultaneously selective catalytic reduction by NH3 (NH3-SCR) and CO oxidation. The introduction of CuO provided the active sites for the oxidation of CO, while inhibited the NH3-SCR process and facilitated the generation of N2O by-product at high temperature. Accordingly, a catalyst coupling system was designed by employing 1V-5W/Ti and 2Cu-1V-5W/Ti catalysts in one reactor, and high NO conversion (>90 %) and CO removal efficiency (>80 %) could be simultaneously realized within 350–500 °C. This work would provide valuable insights for achieving simultaneous removal of NOx and CO using the catalyst coupling method.