Preparation of Cr–Ti Binary Oxide Anchored Mesoporous Silica by CVD Method and Their Photocatalytic Activities

Kamegawa, Takashi; Shudo, Takehiro; Yamashita, Hiromi

doi:10.1007/s11244-010-9486-8

Cited by 14 publications

(8 citation statements)

References 24 publications

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“…Since it is widely accepted that the active sites of redox catalytic processes are tetrahedral transition metal ions [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], we have looked for the method that allow removing the Al atoms from the zeolite and then incorporating the transition metal ions in its framework to obtain isolated metal single-site catalyst. However, there is the problem to obtain single-site catalyst with identical and well separated active sites related to two types of complexity, one arising from the oxide support and the other from the precursor aqueous solution.…”

Section: Introductionmentioning

confidence: 99%

Preparation of two series of VxSiBeta zeolite catalysts with V centres in framework and extra-framework positions and their application in selective oxidation of methanol

Trejda

Millot

Chałupka

et al. 2019

Applied Catalysis A: General

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A B S T R A C TTwo series of V-containing Beta zeolites have been prepared by contacting of the aqueous NH 4 VO 3 solution with two SiBeta zeolites at pH = 2.5 and 6, respectively. Because of the presence in NH 4 VO 3 solution at pH = 2.5 mainly monomeric VO 2 + ions, vanadium have been easily incorporated into framework of SiBeta zeolite as pseudo-tetrahedral non hydroxylated (SiO) 3 V = O and hydroxylated (SiO) 2 (OH)V = O species. The moderate nucleophilicity of the basic vanadyl oxygen of the latter species play important role in methanol oxidation toward formaldehyde. The selectivity toward formaldehyde on this series of V x SiBeta(I) increases with the amount of pseudo-tetrahedral hydroxylated (SiO) 2 (HO)V = O species, which act as either redox or acidic and basic centres. In contrast at pH = 6, the aqueous NH 4 VO 3 solution is expected to contain both mononuclear and polynuclear V ions, thus it is more difficult to incorporate V species in SiBeta at this condition as shown by FT-IR and NMR data. The absence of pseudo-tetrahedral V species in framework position of V 0.6 SiBeta(II) is probably responsible for lack of activity of this catalyst in methanol oxidation. The appearance of this species in the series of V x SiBeta(II) zeolites for high V content leads to their activity in methanol oxidation toward formaldehyde.

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Section: Introductionmentioning

confidence: 99%

Preparation of two series of VxSiBeta zeolite catalysts with V centres in framework and extra-framework positions and their application in selective oxidation of methanol

Trejda

Millot

Chałupka

et al. 2019

Applied Catalysis A: General

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“…The purpose of the present work is to improve the rate of CHA oxidation while maintaining high oxidation selectivity. Some literature reports that Ti species, when incorporated into Cr-containing materials, enhances the photocatalytic activity under visible-light irradiation, even though Ti species does not absorb visible light. − Rodrigues et al reported that MCM-48 containing Cr and nanosized TiO 2 , prepared by a hydrolysis of TEOS, Cr(NO 3 ) 3 , and titanium tetraisopropoxide (TTIP), shows higher activity for degradation of acetaldehyde in the gas phase than MCM-48 containing Cr alone. Shen et al reported that MCM-41 containing Cr and Ti species, prepared by a hydrolysis of TEOS, Cr(NO 3 ) 3 , and tetrabutyl titanate, promotes water splitting with higher activity than MCM-41 containing Cr alone.…”

Section: Introductionmentioning

confidence: 99%

“…Shen et al reported that MCM-41 containing Cr and Ti species, prepared by a hydrolysis of TEOS, Cr(NO 3 ) 3 , and tetrabutyl titanate, promotes water splitting with higher activity than MCM-41 containing Cr alone. Kamegawa et al reported that MCM-41 containing Cr and Ti species, prepared by a chemical vapor deposition with TiCl 4 and CrO 2 Cl 2 , promotes photopolymerization of ethylene with higher activity than MCM-41 containing Cr alone. All these reports suggest that the incorporation of Ti to Cr-containing materials probably produces an oxo-bridged Cr–O–Ti species and shows enhanced activity, although the direct evidence for the formation of Cr–O–Ti species and the mechanism for activity enhancement are not provided.…”

Section: Introductionmentioning

confidence: 99%

Visible-Light-Induced Partial Oxidation of Cyclohexane by Cr/Ti/Si Ternary Mixed Oxides with Molecular Oxygen

et al. 2011

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Cr/Ti/Si ternary mixed oxides (CrTiSi) were prepared by a hydrolysis of tetraethyl orthosilicate (TEOS), Cr(NO3)3, and titanium tetraisopropoxide (TTIP) followed by calcination. These oxides were used as catalysts for partial oxidation of cyclohexane with molecular oxygen under irradiation of visible light (λ > 400 nm). The CrTiSi catalysts produce cyclohexanol and cyclohexanone with high selectivity (>91%) and show much higher activity than the CrSi binary oxides. Among them, the catalyst with equimolar amounts of Cr and Ti shows the highest activity. Visible-light irradiation of the CrSi catalyst promotes a reduction of tetrahedrally coordinated Cr oxide species (T d 6+) and produces the excited state (T d 4+*), which behaves as an active site for oxidation. In contrast, the CrTiSi catalyst contains tetrahedrally coordinated Cr and Ti oxide species that are connected through the Cr–O–Ti bond. The photoformed T d 4+* species is strongly stabilized due to delocalization of excited electrons on the Cr–O–Ti species. This suppresses rapid deactivation of T d 4+* and results in enhanced photocatalytic activity.

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“…In this study, we focused on a grafted titanium complex having a tunable coordination state. Generally, such isolated transition-metal species can be realized in porous silica networks, where they have specific tetrahedral coordination states exhibiting highly selective redox properties in the presence of oxidants and/or under photoirradiation. , In addition, because their catalytic activities are strongly dependent on the local environment around the isolated active species, their coordination design has been investigated using both bottom-up ,, and postmodification techniques. ,− However, as such species are presented in rigid three-dimensional (sometimes nonordered) silica networks, molecular-level design of their chemical environments is not typically possible. Furthermore, because of the formation of unusual tetrahedrally coordinated species due to the isolation of the transition metals within the silica matrix, it is difficult to obtain the respective isolated sites with high surface densities.…”

Section: Introductionmentioning

confidence: 93%

Photocatalytic Activation of C–H Bonds by Spatially Controlled Chlorine and Titanium on the Silicate Layer

et al. 2019

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Owing to the economic and environmental benefits, photocatalytic organic transformation via C–H activation is a crucially important, while still challenging area. We report a photocatalytic process for partial cyclohexane oxidation with enhanced catalytic activity that exploits chlorine and titanium atoms spatially arranged on a silica substrate. Silica-based catalysts bearing grafted titanium that effectively interacts with photochemically adsorbed chlorine were prepared. The catalysts were synthesized by reacting a layered silicate with titanium(IV) acetylacetonate and subsequent chlorination treatment. Characterization by a variety of techniques revealed that the organic ligand of the titanium species that is grafted onto the silicate layer surface is converted into chlorine while maintaining its coordination state. However, upon subsequent hydration, the chlorine existed as HCl. We investigated the performance of the catalyst for the production of cyclohexanol and cyclohexanone from cyclohexane with molecular oxygen under solar light irradiation. The chlorinated layered silicate photocatalyst exhibited a remarkably high production rate (0.7 mmol g–1 h–1) and large amount of product formed (0.8 mmol), while the overoxidation of cyclohexane was inhibited. The enhanced catalytic ability could be explained by the presence of a radical mediator (chlorine) located at a position neighboring an isolated titanium atom. The high surface density of these active species (both titanium and chlorine) on the silicate layer provided suitable electron transfer to form chlorine radicals.

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Preparation of Cr–Ti Binary Oxide Anchored Mesoporous Silica by CVD Method and Their Photocatalytic Activities

Cited by 14 publications

References 24 publications

Preparation of two series of VxSiBeta zeolite catalysts with V centres in framework and extra-framework positions and their application in selective oxidation of methanol

Preparation of two series of VxSiBeta zeolite catalysts with V centres in framework and extra-framework positions and their application in selective oxidation of methanol

Visible-Light-Induced Partial Oxidation of Cyclohexane by Cr/Ti/Si Ternary Mixed Oxides with Molecular Oxygen

Photocatalytic Activation of C–H Bonds by Spatially Controlled Chlorine and Titanium on the Silicate Layer

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