Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity, Recycling and Regeneration

Salinier, Valérie; Niccolaï, Gerald P.; Dufaud, Véronique; Basset, Jean‐Marie

doi:10.1002/adsc.200900274

Cited by 22 publications

(13 citation statements)

References 46 publications

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“…Careful recycling studies of the heterogeneous catalysts showed significant degradation of activity for the (highly active) catalysts that contained acac ligands, but little deactivation for the (less active) catalysts that did not contain any acac. Through use of detailed kinetic studies coupled with characterization of the catalysts before and after reaction, the authors identified two factors that contributed to the activity loss, loss of zirconium by cleavage of surface siloxide bonds and exchange reactions between acetylacetonate ligands and alcohols in the substrate/product solution [59]. Catalyst regeneration was carried out by addition of acac to the supported catalyst, with this addition leading to greatly enhanced activity.…”

Section: Deactivation and Stability In Surfacementioning

confidence: 99%

“…They developed silica supported zirconium complexes from a SOMC approach using Zr(acac) 4 as a reagent and applied the materials in the catalytic transesterification of acrylates [59]. The reactivity of the complexes was compared to similar molecular catalysts such as Zr(acac) 4 and Zr(O-n-Bu) 4 , with high activity found to be associated with the presence of acac ligands.…”

Section: Deactivation and Stability In Surfacementioning

confidence: 99%

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On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

2010

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Research on heterogenized metal complex catalysts has been carried out for 40 years. Despite thousands of published catalysts, there are only two significant commercial processes that utilize supported metal complex catalysts. Most academic papers are simply ''demonstration of concept'' studies reporting myriad ways to support various metal complex catalysts. Too few papers focus on rigorous studies of reaction kinetics, catalyst recycle, catalyst stability and deactivation pathways. Here, preliminary stability and deactivation studies of supported enantioselective Co-salen epoxide ring-opening catalysts and enantioselective Ru-salen olefin cyclopropanation catalysts are summarized. Insights with regard to catalyst deactivation suggest methodologies for catalyst stabilization, allowing for more effective catalyst recycle and enhanced catalyst turnover. Further examples where supported metal complex catalysts are applied in commercial processes will require the field to shift focus from ''demonstration of concept'' studies to more detailed investigations of catalyst stability and recyclability.

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Section: Deactivation and Stability In Surfacementioning

confidence: 99%

Section: Deactivation and Stability In Surfacementioning

confidence: 99%

On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

2010

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“…Compared with the spectrum of pure agarose gel, the spectrum of the composite shows a slightly decreased intensity of the spectral band centered around 70 ppm, which mainly corresponds to carbons bonded to OH, and accordingly increased intensity around 75 ppm. These spectral differences may be attributed to the conversion of C–O–H to C–O–Zr, which changes the involved 13 C chemical shifts from 70 to 75 ppm . The direct‐polarization (DP) 13 C spectra in Fig.…”

Section: Resultsmentioning

confidence: 99%

Aqueous Route Synthesis of Mesoporous ZrO₂ by Agarose Templation

Klosterman

et al. 2012

J. Am. Ceram. Soc.

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Mesoporous zirconia with high surface area has been synthesized using self‐assembling agarose gel as a template. Agarose gel was formed in the presence of aqueous zirconyl nitrate solutions followed by precipitation of zirconium (hydr)oxide in the gel framework. A porous zirconia structure is obtained by pyrolysis of agarose. Fourier transform infrared spectroscopy is employed to assess the agarose‐zirconia precursor interaction. Changes in the C–O absorption bands indicate zirconium association with the OH groups of the agarose. Solid state 13C NMR studies of the nanocomposite showed a shift in intensity from 70 to 75 ppm indicating conversion of ~7% of C–O–H to C–O–Zr. Scanning electron microscopy reveals that both agarose/zirconia nanocomposite and zirconia have similar morphological features as that of pure agarose gel confirming agarose templation. Phase transformation of zirconia from amorphous to tetragonal between 300°C and 500°C, and gradually into monoclinic phase up to 900°C is observed using X‐ray powder diffraction. Specific surface area and pore size distribution are determined using nitrogen adsorption, employing BET and Barrett–Joyner–Halenda methods, respectively. The specific surface area of porous zirconia after heat treatment at 500°C was determined to be 86 m2/g, which reduced with increasing temperature to 13 m2/g above 900°C. Transmission electron microscopy confirmed the hierarchical structure of porous zirconia.

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“…A report on the catalytic study is presented in the part 2 of this series. [25] Experimental Section…”

Section: Discussionmentioning

confidence: 99%

Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1. Synthesis and Characterization

et al. 2009

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Various silica-supported acetylacetonate and alkoxy zirconium(IV) complexes have been prepared and characterized by quantitative chemical measurements of the surface reaction products, quantitative surface microanalysis of the surface complexes, in situ infrared spectroscopy, CP-MAS 13 C NMR spectroscopy and EXAFS. The complex A C H T U N G T R E N N U N G ( SiO)ZrA C H T U N G T R E N N U N G (acac) 3 (acac = acetylacetonate ligand) (1) can be obtained by reaction of zirconium tetra- 4 ] with a silica surface previously dehydroxylated at 500 8C. The complexes 3 Zr À H with, respectively, acetylacetone and nbutanol at room temperature. The spectroscopic data, including EXAFS spectroscopy, confirm that in compound 1 the zirconium is linked to the surface by only one Si À O À Zr bond whereas in the case of compounds 2 and 3 the zirconium is linked to 3 surface oxygen atoms which are sigma bonded. EXAFS data indicate also that the acetylacetonate ligands behave as chelating ligands leading to a hepta-coordination around the zirconium atom in 1 and a penta-coordination in 2. In order to provide a molecular analogue of 1, the synthesis of the following polyoligosilsesquioxane derivative (c-C 5 H 9 ) 7 (1') was achieved. The compound 1' is obtained by reacting (c-C 5 H 9 ) 7 Si 8 O 11 A C H T U N G T R E N N U N G (CH 3 ) 2 (OH), 4, with an equimolecular amount of ZrA C H T U N G T R E N N U N G (acac) 4 . In the same manner, syntheses of complexes (c-C 5 H 9 ) 7 Si 7 O 12 ZrA C H T U N G T R E N N U N G (acac) (2') and of (c-C 5 H 9 ) 7 Si 7 O 12 ZrA C H T U N G T R E N N U N G (O-n-Bu) (3') were achieved by reaction of the unmodified trisilanol, (c-C 5 H 9 ) 7 Si 7 O 9 (OH) 3 , with respectively ZrA C H T U N G T R E N N U N G (acac) 4 and ZrA C H T U N G T R E N N U N G (O-n-Bu) 4 at 60 8C in tetrahydrofuran. Compounds 1', 2' and 3' can be considered as good models of 1, 2 and 3 since their spectroscopic properties are comparable with those of the surface complexes. The synthetic results obtained will permit us to study the catalytic properties of these surface complexes and of their molecular analogues with the ultimate goal of delineating clear structure-activity relationships.

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Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity, Recycling and Regeneration

Abstract: The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica-supported acetyl-

Cited by 22 publications

References 46 publications

On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

Aqueous Route Synthesis of Mesoporous ZrO₂ by Agarose Templation

Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1. Synthesis and Characterization

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Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2. Activity, Recycling and Regeneration

Abstract: The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica-supported acetyl-

Cited by 22 publications

References 46 publications

On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

On the Stability and Recyclability of Supported Metal–Ligand Complex Catalysts: Myths, Misconceptions and Critical Research Needs

Aqueous Route Synthesis of Mesoporous ZrO2 by Agarose Templation

Silica‐Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1. Synthesis and Characterization

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Aqueous Route Synthesis of Mesoporous ZrO₂ by Agarose Templation