Large pore ti-beta zeolite with very low aluminium content: An active and selective catalyst for oxidations using hydrogen peroxide

Camblor, Miguel Á.; Costantini, M.; Corma, Avelino; Esteve, Patricia; Gilbert, L.; Martı́nez, Agustı́n; Valencia, Susana

doi:10.1016/s0926-9614(96)80029-3

Cited by 5 publications

(6 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Experimental details of the synthesis procedures have been already described elsewhere, ,− except for the Al-containing Beta(F) series. In this case, the same experimental procedure as in the Al-free syntheses 9 was followed, but metal Al was dissolved in TEAOH and then added to the synthesis gel at the end of the preparation.…”

Section: Methodsmentioning

confidence: 99%

“…One of the challenges in this field is to understand why different Ti-zeolites seem to have different catalytic properties, beyond those that can be explained by mere shape selectivity constraints imposed by the size and shape of their channels, even if isolated Ti species were incorporated in all cases into the framework. Notably, the most interesting Ti-zeolites, TS-1 and Ti−Beta, exhibit a markedly different behavior, exemplified by their different activity and selectivity dependence on the solvent. , Differences between the “intrinsic” activity and selectivity of both materials were early attributed to the presence of Al in Ti−Beta, but once the synthesis of Ti−Beta was made possible in the absence of Al, , the differences between the catalytic behavior of these zeolites persisted. We have very recently developed new methods to synthesize Ti−Beta zeolites with a wide range of chemical compositions and physical properties. − Here we report on the state of Ti in Al-free Ti−Beta zeolite prepared by different routes, the different physicochemical properties of these materials, and the implications of these differences on their catalytic behavior for alkenes epoxidation.…”

Section: Introductionmentioning

confidence: 99%

“…Notably, the most interesting Ti-zeolites, TS-1 and Ti−Beta, exhibit a markedly different behavior, exemplified by their different activity and selectivity dependence on the solvent. , Differences between the “intrinsic” activity and selectivity of both materials were early attributed to the presence of Al in Ti−Beta, but once the synthesis of Ti−Beta was made possible in the absence of Al, , the differences between the catalytic behavior of these zeolites persisted. We have very recently developed new methods to synthesize Ti−Beta zeolites with a wide range of chemical compositions and physical properties. − Here we report on the state of Ti in Al-free Ti−Beta zeolite prepared by different routes, the different physicochemical properties of these materials, and the implications of these differences on their catalytic behavior for alkenes epoxidation. We conclude that the main differences observed in the activity and selectivity of TS-1 and Ti−Beta in the epoxidation of alkenes are essentially related to their different crystalline structures and cannot be solely attributed to other parameters as previously suggested (presence of Al, presence of defects, hydrophilicity).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite

et al. 1998

View full text Add to dashboard Cite

Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F- medium and has produced hydrophobic selective oxidation catalysts. The Ti−Beta(F) materials have been characterized by X ray diffraction, infrared, Raman, ultraviolet, XANES, EXAFS, 29Si MAS NMR, and 1H→29Si CP MAS NMR spectroscopies, adsorption microcalorimetry, and catalytic testing. At near neutral pH the incorporation of Ti into the framework appears to present an upper limit of ca. 2.3 Ti/uc, beyond which anatase is detected in the calcined materials. However, at higher pH (ca. 11) larger amounts of Ti can be incorporated without anatase formation. After calcination, Ti incorporation in the framework is characterized by an increase in the unit cell volume, the appearance of one Raman band and three infrared bands in the region near 960 cm-1 and the presence of a strong absorption band in the 205−220 nm ultraviolet spectrum. By 29Si MAS NMR, 1H→29Si CP MAS NMR, and infrared spectroscopies it is concluded that upon contact with ambient humidity there is no hydrolysis of Si−O−Ti bonds in Ti−Beta zeolites prepared by the fluoride route, while it is probably a major feature of those synthesized in OH- medium. XANES and EXAFS spectroscopies of calcined dehydrated Ti−Beta zeolites unambiguously demonstrate the tetrahedral coordination of Ti with a Ti−O bond length of ca. 1.80 Å. Upon hydration, the changes in the XANES and EXAFS spectra are consistent with a change in the coordination of Ti to reach a state which depends on the composition and synthesis route and which ranges from a 5-fold coordination for Al-free Ti−Beta synthesized by the F- method to a highly distorted 6-fold coordination in Ti,Al−Beta synthesized in OH- medium. Adsorption microcalorimetry experiments show the strict hydrophobic nature of pure SiO2 zeolite Beta synthesized in F- medium while evidencing a slight increase in the hydrophilicity of the material upon incorporation of Ti to the framework. This is due to the relatively strong adsorption of precisely one H2O molecule per Ti site. On the contrary, the materials synthesized in OH- medium show an enhanced hydrophilicity. Finally, Ti−Beta(F) is an active and selective catalyst for oxidation of organic substrates with H2O2. A comparison of the activities and selectivities of Ti−Beta(F), Ti−Beta(OH) and TS-1 in the epoxidation of 1-hexene using acetonitrile and methanol as solvents demonstrates that the major differences between Ti−Beta and TS-1 catalysts are intrinsic to each zeolitic structure. Because of its high hydrophobicity, Ti−Beta(F) catalyst can advantageously replace Ti−Beta(OH) in the epoxidation of substrates, like unsaturated fatty acids or esters, which contain a polar moiety.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite

et al. 1998

View full text Add to dashboard Cite

show abstract

“…However, controlling the synthesis conditions, for instance, with F - medium instead of the most usual OH - , it is possible to reduce the content of framework defects in Ti-zeolite samples. − Applying this technique in the synthesis of Ti-β, it has been observed in a recent study that most of the Ti centers in the dehydrated sample are fully connected to the framework, and this structure is stable even after rehydration and subsequent calcination. In addition, these nondefective materials show a good catalytic activity.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Ti-Zeolites with Water. A Periodic ab Initio Study

1999

View full text Add to dashboard Cite

The interaction of water molecules with Ti sites in Ti-containing zeolites has been studied by means of the ab initio periodic Hartree-Fock program CRYSTAL. The zeolitic part of the system has been represented by a perfect crystalline chabazite framework. The Ti content and distribution within the model structure have been designed so as to keep the maximum symmetry. Water physisorption has been accomplished by adding one (two) water molecule to each symmetry equivalent Ti-site; the geometry has been fully optimized; the calculated adsorption energy is -34.4 ( -43.6) kJ mol -1 . The stability and electronic structure of the hydrated sites are shown to be largely dependent on the framework flexibility. The hydrolysis of the Ti-O-Si bridge to yield Ti-OH and Si-OH has also been studied. This reaction is endothermic within the present model (∆E ) 35.3 kJ mol -1 ). The activation energy was estimated in about 84 kJ mol -1 .

show abstract

“…Some reaction parameters such as solvent effects, catalyst properties (external surface, pore size, and crystal size), and different metal incorporation have been identified for TS-1. [3][4][5][6][7][8][9][10][11] Recently, UOP LLC's scientists investigated the redoxsilicalites, incorporated with both titanium and tin into the framework structure (Ti-Sn-S-1) for epoxidation of olefins. 12 Ti-Sn-S-1 shows excellent improved catalytic activity and stability.…”

mentioning

confidence: 99%