TS-1 Catalyst Research Articles

Vanadium-Modified TS-1 Catalysts with Enhanced Lewis Acid and Charge Density for Efficient Hydroxylation of Benzene to Phenol

Vanadium-Modified TS-1 Catalysts with Enhanced Lewis Acid and Charge Density for Efficient Hydroxylation of Benzene to Phenol

Intracrystalline diffusion regulation of Au/hierarchical TS-1 for simultaneously enhanced stability and selectivity in propene epoxidation with H2 and O2

Regulation of intracrystalline diffusion plays a pivotal role in ensuring the catalytic stability of metal-supported zeolite catalysts. Herein, we successfully achieved precise modulation of intracrystalline diffusion in Au-loaded hierarchical TS-1 catalysts by two-step recrystallization approach. This modulation was achieved by manipulating the length of mesoporogens, characterized by the hierarchical factor (HF). The HF could be used as the descriptor to reveal the reaction stability and deactivation process including blocking degree (VAu: gold volume / Vna: volume not accessible for N2) by the Au nanoparticles and coke formation in fresh and used catalysts, respectively. In addition, the enhanced selectivity was attributed to the improved hydrophobicity of Au/hierarchical TS-1 with gradually decreased terminal silanols by two-step recrystallization approach. This work not only provides the new strategy for the regulation of zeolite intracrystalline diffusion, but also could shed new lights on the industrial process of direct propene epoxidation with H2 and O2.

3D printed cross-scale structured TS-1 catalysts for continuous scale-up reactions

Structured catalysts and reactors have great application prospects in gas-liquid conversion engineering due to excellent process intensification. However, the conventional fabrication process limits the designability of the hierarchical structure of monolithic catalysts, the establishment of structure-activity relationships, and slows down the speed of catalyst development. Here, we establish a structure-activity mechanism for cross-scale structures of a 3D-printed functionally gradient modular monolithic TS-1 catalyst (FGMMC) and catalytic performance by adjusting hierarchical structure distribution based on catalytic reaction simulations. The effects of uniform and gradient structures with different TS-1 contents and unit cell sizes on the catalytic properties of modular monolithic TS-1 catalyst (MMC) were investigated. In one-step scale-up reactions of ethylene to high-value-added ethylene glycol (EG), FGMMC exhibits superior catalytic efficiency than traditional powder, extrusion-dripping beads, and uniform catalysts. After a 27-h continuous scale-up catalytic test, FGMMCs exhibit excellent wear resistance (only 1.39% mass loss) and an outstanding EG yield of 82.5%. 3D-printed FGMMCs act as self-activators with a 37% reaction rate increase after rapid post-activation treatments. This work provides a low-cost and recyclable manufacturing method for achieving the functional and structural integration of catalysts and reactors by 3D printing while predicting and rapidly validating scale-up reactions.

Epoxidation of Light Olefin Mixtures with Hydrogen Peroxide on TS-1 Catalyst

The direct epoxidation of mixed ethene and propene feedstocks using hydrogen peroxide over a titanium silicalite (TS-1) catalyst was investigated within a continuous trickle bed reactor operating in laboratory scale. Methanol was employed as the reaction solvent. This study aimed to streamline the epoxidation process by obviating the need for prior separation of alkenes, thereby enhancing process efficiency. An extensive array of operational parameters was explored in a trickle bed reactor, encompassing experimental parameters such as temperature, total pressure, hydrogen peroxide concentration, liquid flow rate, and gas composition. In contrast to prior investigations involving separate ethene and propene epoxidation, this study revealed a reduction in epoxide selectivity. The principal by-products observed were methoxy species, formed through the interaction between the epoxide and methanol, resulting in a ring-opening reaction. The influence of water on this ring-opening process was negligible. Notably, the tunability of the system was demonstrated, highlighting low temperature and elevated partial ethene pressure as pivotal factors for augmentingthe epoxide selectivity. The findings suggest that binary olefin mixtures exhibit diminished selectivity but improved stability. This behavior is potentially linked to the olefin solubility in methanol, or alterations in the surface species concentrations, typically associated with catalyst activity variations. These insights offer a valuable foundation for understanding and optimizing the direct epoxidation of mixed ethene and propene feedstock.Graphical

Approaching High-Performance TS-1 Zeolites in the Presence of Alkali Metal Ions via Combination of Adjusting pH Value and Modulating Crystal Size.

Lewis acid zeolites play an important role in industrially important green reactions closely related to fine chemical and biomass conversion. Titanium-doped TS-1 zeolite is a milestone Lewis acid zeolite widely used in industrially significant green oxidation processes with hydrogen peroxide as an oxidant under mild conditions. TS-1 zeolites are normally synthesized in basic conditions under hydrothermal treatment. Up to now, there has still been no success in synthesizing active TS-1 Lewis acid zeolites by using inorganic alkali, e.g., NaOH or KOH as base, which is cheaper and more stable compared to the quaternary ammonium hydroxide or organic amines used in traditional synthesis. Here, an inorganic base of NaOH was employed in synthesizing active TS-1 zeolites for the first time. The crucial factor was the control of adverse effects of sodium cations on the incorporation of active titanium cations. Higher catalytic activity was achieved by further reducing the size of the TS-1 crystal by using the seed-added strategy, which uses the catalytic activity of a commercial catalyst, the production cost being much lower than commercial TS-1 catalysts, indicating great commercial potential and the possibility of preparing other cheap Lewis acid catalysts by using inorganic alkali.

Optimization of MOFs-induced strategy for preparing anatase-free hierarchical TS-1 towards 1-hexene epoxidation: TPAOH dosage regulation, silanization and stabilizing acidic sites

Metal organic frameworks (MOFs)-induced synthetic strategy has been proven a convenient and efficient way for preparing anatase-free hierarchical TS-1 zeolite in our previous study. Here, to further enhance the catalytic performance on 1-hexene, the MOFs-induced hydrothermal synthesis route is optimized by adjusting the amount of tetrapropylammonium hydroxide (TPAOH) and performing different degrees of silanization treatment. A low TPAOH dosage can ensure the synthesized samples have abundant and dense active framework Ti at the expense of partial hierarchical structure. Further deep silanization treatment created mesoporous structure ranging between 20 and 30 nm without affecting the content or distribution of active titanium. The obtained anatase-free hierarchical TS-1 sample Sil-0.150 possesses excellent 1-hexene conversion of >38%. Based on detailed NH3-TPD and Py-IR tests, the presence of high-density Lewis acid sites (LAS) leads to a decreased epoxy product selectivity of 91.5%, and the optimized MOFs-induced synthesis strategy may open up new perspectives for the design and application of high-performance TS-1 catalysts in selective epoxidation reactions of various alkenes.

TS-1 Synthesis via Subcrystal Aggregation: Construction of Highly Active Hydrogen-Bonded Titanium Species for Alkene Epoxidation.

The construction and determination of highly active Ti sites comprise one of the most significant challenges in the rational design and synthesis of Ti-containing porous catalysts. The pathway to efficiently build highly catalytically active titanium species remains to be proposed in spite of deliberate post treatments or ambiguous batch composition adjustments. In this study, we developed a bottom-up strategy to construct a TS-1 catalyst with highly active hydrogen-bonded Ti species via subcrystal aggregation crystallization. The microstructure of the hydrogen-bonded Ti species was verified by vacuum FT-IR and 1H MAS SSNMR spectroscopies. Noteworthy features of the hydrogen-bonded Ti species were also revealed, including a pentahedral coordination state and Brønsted acidity, as identified by the UV-Raman, XPS, XAFS, and FT-IR spectra of adsorbed pyridine. Significantly, the hydrogen-bonded Ti species exhibits extraordinary activity in allyl chloride epoxidation (nearly 70% higher than that of traditional Ti species). This study provides a new approach to building highly active Ti sites, which may provide new insights into the design and synthesis of high-performance titanosilicate catalysts.

Ti-MWW Catalysts for Propylene Oxide Production: Influence of Si/Ti Ratio and Calcination Conditions

Titanium silicates of MWW structures with different Si/Ti ratios were prepared via hydrothermal synthesis using piperidine as the structure directing agent and boric acid as the crystallization agent. All the syntheses resulted in highly crystalline materials independent of the Si/Ti ratio. The observed morphology showed MWW-like well-defined thin hexagonal platelets. The synthesized Ti-MWW materials exhibited higher surface areas and partial meso-porosity compared to the commercial TS-1 catalyst. The coordination of the Ti-species was investigated by UV–vis- and IR-spectroscopy. The MWW titanium silicates were tested for the catalytic performance in the epoxidation of propylene in a laboratory-scale trickle bed reactor to compare their clear different physico-chemical properties with the commercial TS-1. The synthesized Ti-MWW materials showed significantly higher catalytic activities, up to 3.5 times, using acetonitrile as the solvent and enhanced epoxide selectivities partially up to 100% in methanol unlike TS-1. The effect of the Ti content in the MWW and the calcination conditions were investigated in propylene epoxidation, revealing the beneficial effect of a lower calcination temperature and an increased Ti content on the activity. The catalytic results were correlated with the physico-chemical properties of the synthesized materials.Graphical

Effect of the bipodal Ti species on activity and selectivity of propylene epoxidation with H2O2 over TS-1: A theoretical study

In order to probe into the effect of bipodal Ti species on the catalytic performance, the propylene epoxidation with H2O2 over TS-1 catalyst with bipodal Ti site has been studied using an embedded quantum mechanical/molecular mechanics (QM/MM) approach, and the results shown that the bipodal Ti site has strong Brønsted and Lewis acidity, which not only greatly facilitates the epoxidation reaction but also lower selectivity toward the epoxy products. The excellent epoxidation activity is attributed to the Lewis acidity, in which, H2O2 easily activated to generate active intermediates (i.e., Ti-η1-OOH and Ti-η2-OOH) that is facile to transfer O atom to oxidize the propylene. The poor selectivity toward PO is also due to the Lewis acidity, which leads to the stronger adsorption ability of PO and excellent ring-opening ability of Ti-OH nucleophile to PO. The introduction of methoxy (CH3O) group is beneficial for the enhancement of the selectivity of PO, although it enhances the activation free energy for epoxidation to generate PO. The identifications about the relationship of the intrinsic selectivity and activity with bipodal Ti site would provide a clue for designing highly-efficient TS-1 catalysts in propylene epoxidation to PO from the theoretical point of view.

Controllable synthesis of a large TS-1 catalyst for clean epoxidation of a C=C double bond under mild conditions

Controllable synthesis of a large TS-1 catalyst for clean epoxidation of a C=C double bond under mild conditions

Insights into the mechanism of the solvolysis of propylene oxide over titanium silicalite-1: a theoretical study.

In order to probe into the mechanism of solvolysis (alcoholysis/hydrolysis) of propylene oxide (PO), the formation of propylene glycol (PG), 1-methoxy-2-propanol (PPM) and 2-methoxy-1-propanol (SPM) over the TS-1 catalyst with tetrahedral Ti and Ti/defect sites was systematically discussed using an embedded quantum mechanical/molecular mechanics (QM/MM) approach. The results showed that the activity of PO solvolysis is closely related to the ring-opening ability of active substances, and the ring-opening ability is in the following order: Si-O(H)-Ti > Ti-OH > 5MR Ti-OOH > Ti-OCH3 (tetrahedral Ti site); 3MR Ti-OOH > Ti-OH > 5MR Ti-OOH > Ti-OCH3 (Ti/defect site). At the tetrahedral site, the concerted mechanism is the dominant pathway for PO ring opening to form PPM, while a competitive relationship exists between stepwise and concerted mechanisms to form PG and SPM. Si-O(H)-Ti exhibits excellent PO ring-opening activity because of its strong Brønsted acidity, but it is difficult to form. At the Ti/defect site, the stepwise mechanism via PO ring opening with 3MR Ti-OOH and then successive hydrolysis/alcoholysis to form product is the dominant pathway. The overall energy barrier of the optimal route is relatively lower as compared to the tetrahedral Ti site. This work opens up a new path for providing more information on the detailed mechanism in the solvolysis of PO over the TS-1 catalyst from a theoretical point of view.

Synthesis of ultra-fine TS-1 catalyst with high titanium content and its performance in phenol hydroxylation

The study of simultaneous control over framework Ti and particle size was achieved using the incorporation of NH4HCO3 and PVA into the synthesis medium of the TS-1 catalyst.

The selective hydrodeoxygenation of guaiacol to cyclohexanol over cobalt-modified TS-1 catalysts

A Co-modified zeolite (Co/TS-1) catalyst is prepared and evaluated for the catalytic hydrodeoxygenation (HDO) of the lignin-derived model compound guaiacol under mild conditions at 1 MPa H2 and 200 °C. According to the systemic experimental investigations including reduction temperatures, metal loading and reaction time, it is found that the guaiacol conversion and cyclohexanol selectivity over guaiacol HDO are significantly improved by regulating the Ti content, Co content and reduction temperature, in which 5.0%Co/TS-1 (Si/Ti = 110) reduced in 600 °C shows the superior HDO performance with 94.3% guaiacol conversion and 88.7% cyclohexanol selectivity. Combined with XRD, TEM, BET, NH3-TPD, Py-IR, H2-TPR, UV–Vis and XPS characterizations, it is confirmed that the introduction of appropriate Ti could modulate the catalyst Lewis acid sites and the interaction between Co and support to affect the metal reduction degree, to realize the improvement of the substrate adsorption and exposing more metallic Co0 active sites, resulting in higher HDO performance. In addition, the reaction pathway of guaiacol HDO to cyclohexanol over Co/TS-1 is proposed via demethoxylation of guaiacol to generate reaction intermediate phenol.

Recent advances in the synthesis of TS-1 zeolite.

Heteroatomic zeolites as an important class of zeolites, have been widely applied in industrially catalytic processes due to their unique properties. As one of the most representative heteroatomic zeolites, titanosilicate zeolites have been extensively used in the selective oxidations of organic substrates with H2O2 such as cyclohexanone ammoximation, epoxidation of alkenes, and phenol hydroxylation. In this review, recent advances in the synthesis of TS-1 zeolite are briefly summarized, including use of low-cost raw materials (organic templates, silicon, and titanium sources), development of new synthesis routes (post-treatment synthesis, dry-gel conversion synthesis, solvent-free synthesis, and microwave-assisted synthesis), and new strategy for enhanced mass transfer in TS-1 crystals (synthesis of hierarchical and nanosized TS-1 zeolite). This review might help researchers to have a deep understanding on the synthesis of TS-1 zeolite and provide a new opportunity for the design and preparation of highly efficient TS-1 catalysts in the future.

Using ammonia solution to fabricate highly active Au/ uncalcined TS‑1 catalyst for gas-phase epoxidation of propylene

Reducing the Au particle size and increasing the number of defective Ti4+ species have been considered effective strategies to boost the catalytic performance of Au–Ti bifunctional catalysts used for propylene epoxidation utilizing H2 and O2. Consequently, the development of an effective method that can simultaneously achieve these goals is of significant scientific and industrial importance. Herein, we demonstrate, for the first time, that the simultaneous immobilization of small Au particles (approximately 1.6 nm) onto uncalcined titanium silicate-1 (i.e., TS-1-B) and facilitation of the formation of defective Ti4+ species can be achieved using a modified deposition–precipitation (DP) method utilizing ammonia solution as the precipitant. The as-synthesized catalyst exhibits a significantly enhanced propylene oxide (PO) formation rate combined with fascinating PO selectivity and hydrogen efficiency, which were better than the reference catalyst prepared via the DP urea (DPU) method and other reported Au/uncalcined TS-1 catalysts. The catalyst structure–performance relationship was established using multiple characterization studies. the ammonia treatment facilitates the hydrolysis of some of the ≡Ti-O-Si≡ bonds into defective Ti4+ species (i.e., Ti(OSi)3OH), which not only provides more active Ti4+ sites but also favors the uniform deposition of Au. This methodology and the insights stated herein may also be applicable for enhancing the dispersion of Au in a variety of zeolite-supported catalysts.

Facile synthesis of nanostructured TiO2-SiO2 powder for selective photocatalytic oxidation of alcohols to carbonyl compounds

In this work, TiO2-SiO2 nanostructured powders with different ratios of 80:20, 60:40, and 40:60 were synthesized via the hydrothermal method. A study of the physicochemical properties of materials was conducted using various characterizations. X-ray diffraction (XRD) method confirms polycrystalline to amorphous nature on increasing Si content which was further confirmed with TEM. The photocatalytic activity and selectivity of as-prepared materials were investigated for the oxidation of benzyl alcohol (BzA) to benzaldehyde (BzAD) with a 99% selectivity under visible light (385–740 nm). Remarkably, TS1 catalyst (TiO2:SiO2 in 80:20 ratio) displays high selectivity for the oxidation of benzyl alcohols and their derivatives to corresponding aldehydes compared to other prepared materials.

3D printing of hierarchically porous monolithic TS‐1 catalyst for one-pot synthesis of ethylene glycol

Structured monolithic catalysts have attracted increasing attention in the petrochemical industry due to their advantages of high heat and mass transfer rate, easy scale-up, and reusability. Herein, we put forward a strategy for one-step preparation of SiO2-based monolithic TS-1 catalysts with optimal hierarchical scaffolds by combining the flow field simulation of the reactor and 3D printing technology. Tunable hierarchical porosity from nano to micro scales, suitable pore characteristics, and numerous active sites have been obtained by innovatively combining the spherical porous structure of TS-1/SiO2 material, direct ink writing (DIW) and post-sintering processes. Combined with computational fluid dynamics (CFD) analysis, the effects of different channel offset angles, axial and radial channel sizes on the 3D printed monolithic TS-1 in the catalytic reaction of one-step oxidation of ethylene to ethylene glycol (EG) were verified. 3D-printed monolithic TS-1 catalysts exhibited superior crush strengths (135.11 N/cm) and extraordinary catalytic efficiency, in which the yield of EG reached 82.7%, and the utilization of hydrogen peroxide reached 85.3%. Moreover, the 3D printed TS-1 monolith maintained high catalytic performance over 5 reusable cycles, which solved the problem that traditional catalysts are difficult to be manufactured, separated, and recycled, and presented considerable prospects in reactions requiring fluid agitation.

Effective Synthesis of m-Xylylene Dicarbamate via Carbonylation of m-Xylylene Diamine with Ethyl Carbamate over Hierarchical TS-1 Catalysts.

Carbonylation of m-xylylene diamine (XDA) with ethyl carbamate to produce m-xylylene dicarbamate (XDC), which is the crucial intermediate for the production of m-xylylene diisocyanate (XDI), over the hierarchical TS-1 (HTS-1) zeolite catalyst was studied. The catalysts were characterized by Brunauer–Emmett–Teller, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and temperature-programed desorption of ammonia techniques systematically. The results showed that the high performance of HTS-1 could be attributed to the weak acidity and high Vmeso/Vtotal ratio of the catalyst. Impacts of reaction time and reusage on the HTS-1 catalyst were also investigated. Under 6 h and 200 °C, XDA conversion could reach 100% with 88.5% XDC yield. Furthermore, partial loss of Ti active sites with Lewis acidity on the catalyst surface led to the decrease of XDC yield during recycling. Moreover, a possible reaction mechanism for the title reaction was primarily proposed.

Microwave-Assisted Lignin Wet Peroxide Oxidation to C4 Dicarboxylic Acids.

Innovative methodologies, such as microwave-assisted reaction, can help to valorize lignin with higher productivity and better energy efficiency. In this work, microwave heating was tested in the wet peroxide oxidation of three lignins (Indulin AT, Lignol, and Eucalyptus globulus lignins) as a novel methodology to obtain C4 dicarboxylic acids. The effect of temperature, time, and catalyst type (TS-1 or Fe-TS1) was evaluated in the production of these acids. The TS-1 catalyst improved succinic acid yield, achieving up to 9.4 wt % for Lignol lignin. Moreover, the microwave heating specifically enhanced Lignol conversion to malic acid (34 wt %), even without catalyst, showing to be an attractive path for the future valorization of organosolv lignins. Overall, compared to conventional heating, microwave heating originated a rapid lignin conversion. Nevertheless, for prolonged times, conventional heating led to better results for some target products, e.g., malic and succinic acids.

Insight into the effect of mass transfer channels and intrinsic reactivity in titanium silicalite catalyst for one-step epoxidation of propylene

One-step epoxidation of propylene to propylene oxide (PO) in TS-1/H2O2 system is a promising green and sustainable formation route. However, the TS-1 catalyst is limited by the small pore channels and inadequate intrinsic reactivity. Herein, tetrapropylammonium hydroxide (TPAOH) is used to modify the TS-1 skeleton structures to improve the mass transfer and intrinsic reactivity. Comparative catalytic performance tests indicate that the optimized temperature for TPAOH treatment to modify TS-1 was 90 °C, and the achieved H2O2 utilization efficiency and the PO selectivity can be over 80%. Different TPAOH treatment temperatures significantly influenced the dissolution and recrystallization behavior of TS-1, which altered the composition and microstructure in terms of the pore volume and size, surface properties, and active sites. Our findings indicated that the enlarged pore channels for favorable mass transfer, improved hydrophobic surfaces, enriched framework titanium, and reduced acid strength of titanium silicalite zeolite should be the primary reasons for the enhanced conversion and yields.