Surface Organometallic Chemistry of Titanium on Silica−Alumina and Catalytic Hydrogenolysis of Waxes at Low Temperature

Abstract

Ti(CH2 tBu)4 (1) reacts selectively with the surface silanols of a silica−alumina partially dehydroxylated at 500 °C to provide the monosiloxy species [(SiO)Ti(CH2 tBu)3]SA (2a) and the bisiloxy species [(SiO)2Ti(CH2 tBu)2]SA (2b) in a ca. 40:60 ratio, with concomitant evolution of 1.6 ± 0.2 equiv of neopentane per Ti. These surface complexes were characterized via the combined use of several techniques such as IR spectroscopy, 1H MAS, 13C-CP/MAS, 2D 1H−13C HETCOR, and J-resolved solid-state NMR, as well as mass balance analysis. By treatment under hydrogen at 150 °C the neopentyl ligands in complexes 2a,b undergo hydrogenolysis and a mixture of supported titanium species is obtained. IR, ESR, 1H MAS, and DQ solid-state NMR spectroscopies show the presence of ca. 3% [(SiO)(MsO)TiH2]SA (3a; Ms = Si, Al), 5% [(SiO)(MsO)Ti(Me)−H]SA (3b), 75−80% [(SiO)(MsO)2Ti−H]SA (3c), and 14% [(SiO)(MsO)2TiIII]SA (3d), along with (SiH x ) and (AlH x ) fragments whose formation arise from the opening of adjacent Si−O−M bridges (M = Si, Al). Species 3a−d are efficient catalysts for the hydrogenolysis of waxes with a diesel selectivity higher than 60%. Comparison with the silica-based system shows a beneficial role of the silica−alumina support on the activity of the Ti centers, attributed to a direct interaction of the surface with the active site, which possibly facilitates the β-alkyl transfer, the key C−C bond cleavage step in the proposed mechanism.

Regioselectivity and Reaction Mechanism of Ru‐Catalyzed Hydrogenolysis of Squalane and Model Alkanes

“…[3] Although many microalga strains produce oxygenates such as triglycerides, some strains produce hydrocarbons such as C34 botryococcene from some strains of Botryococcus braunii [4] and C30 squalene (2,6,10,14,18,22-hexaen-2,6,10,15,19,23-hexamethyltetracosane) from Aurantiochytrium, [5,6] both of which are heavy-oil-range hydrocarbons. [8,9] Therefore, conversion of heavier hydrocarbons to lighter ones is an essential process. [7] The F-T process produces am ixture of straight-chain hydrocar-bons with aw ide range of chain lengths including wax (e.g., up to C120).…”

“…[7] The F-T process produces am ixture of straight-chain hydrocar-bons with aw ide range of chain lengths including wax (e.g., up to C120). [8,9] Therefore, conversion of heavier hydrocarbons to lighter ones is an essential process. Conventional methods used for decreasingt he molecular weight of hydrocarbonsa re thermalcracking,c atalytic cracking, and hydrogenolysis (hydrocracking).…”

Synthesis of Zn-MOF incorporating titanium-hydrides as active sites binding H2 molecules

“…This may be ascribed to the nature of Ti-H bond site-isolated to porous scaffold materials. In their FT-IR spectra, aside from showing that the intensity of Ti-H peak was low, its location was reported to be widely shifted from 900 to 1700 cm -1 , depending on its coordination environment and geometry [35][36][37][38]. Furthermore, due to intrinsic instability of this intermediate under an O 2 and H 2 O, we could not use X-ray photoelectron spectroscopy (XPS) to investigate the oxidation state of surface Ti species innate to this material.…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…[424] (SiO) 3 ZrH and (SiO) 2 ZrH 2 react with ethylene with consumption of ZrÀHb ands,a ccording to IR spectroscopy.T he scenario is very similar in the case of Ti [425] and Hf, [426] although asignificant number of Ti III sites are also formed under these conditions. [212] Surface hydrides can also be generated on silica-alumina and alumina (Ti, [431] Zr, [432,433] Hf, [426,434] Ta [435] ). [212] Surface hydrides can also be generated on silica-alumina and alumina (Ti, [431] Zr, [432,433] Hf, [426,434] Ta [435] ).…”

“…[24,[427][428][429][430] With Ta,amixture of the monohydride ( SiO) 2 Ta À Ha nd trishydride ( SiO) 2 TaH 3 has been reported. It has been proposed that the electrophilicity of the Zr and Ti hydrides can be exacerbated by using silica-alumina in place of silica, [431,432] and the formation of cationic zirconium hydrides has been postulated on alumina (Scheme 32 b). It has been proposed that the electrophilicity of the Zr and Ti hydrides can be exacerbated by using silica-alumina in place of silica, [431,432] and the formation of cationic zirconium hydrides has been postulated on alumina (Scheme 32 b).…”