Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.

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Catalytic activity of Co-åkermanite and Co-pyroxene in oxidation reactions

Canadian Journal of Chemistry ◽

10.1139/v11-061 ◽

2011 ◽

Vol 89 (8) ◽

pp. 939-947 ◽

Cited By ~ 5

Author(s):

Irena Mihailova ◽

Dimitar Mehandjiev

Keyword(s):

Catalytic Activity ◽

Solid Phase ◽

Sol Gel ◽

Cobalt Content ◽

Octahedral Coordination ◽

Tetrahedral Coordination ◽

Oxidation Reactions ◽

Oxidation Of Co ◽

Phase Synthesis ◽

Catalytically Active

Two calcium–cobalt silicates were synthesized in which cobalt occupies different structural positions. The crystal phases belong to two main structural silicate types. In the Co-åkermanite structure (Ca2CoSi2O7), cobalt cations take tetrahedral coordination toward oxygen atoms. In the Co-pyroxene structure of CaCoSi2O6, cobalt displays octahedral coordination. Ca2CoSi2O7 was prepared by solid-phase synthesis and CaCoSi2O6 was prepared by sol–gel method. The synthesis of the phases was confirmed by XRD, FTIR, and EPR data. On the basis of the XPS analysis, it can be concluded that Co2+ cations exist in the studied silicates. Thus, it is possible to study the catalytic activity of two silicate phases containing Co2+ cations in different coordinations: tetrahedral and octahedral. It was found that cobalt silicates with crystal structures corresponding to pyroxene and åkermanite possess catalytic activity in the reactions of complete oxidation of CO and toluene. Co-pyroxene exhibits higher catalytic activity than Co-åkermanite, but the higher cobalt content on the surface of Co-pyroxene should also be taken into account. Then, it turns out that catalytically active complexes with Со2+ ions in tetrahedral coordination are more efficient than those with such ions in octahedral coordination when equal concentrations of cobalt were used on the surface of the catalysts.

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Fabrication of Core-Shell Structural SiO2@H3[PM12O40] Material and Its Catalytic Activity

Journal of Nanomaterials ◽

10.1155/2014/835931 ◽

2014 ◽

Vol 2014 ◽

pp. 1-8

Author(s):

Xin Yang ◽

Junhai Wang ◽

Qi Zhang ◽

Xu Wang ◽

Linlin Xu ◽

...

Keyword(s):

Catalytic Activity ◽

Heterogeneous Catalysts ◽

Sol Gel ◽

Operating Conditions ◽

Core Shell ◽

Catalytic Wet Air Oxidation ◽

Air Oxidation ◽

Wet Air Oxidation ◽

Heterogeneous Catalytic ◽

Room Condition

Through a natural tree grain template and sol-gel technology, the heterogeneous catalytic materials based on polyoxometalate compounds H3[PM12O40] encapsulating SiO2: SiO2@H3[PM12O40] (SiO2@PM12, M = W, Mo) with core-shell structure had been prepared. The structure and morphology of the core-shell microspheres were characterized by the XRD, IR spectroscopy, UV-Vis absorbance, and SEM. These microsphere materials can be used as heterogeneous catalysts with high activity and stability for catalytic wet air oxidation of pollutant dyes safranine T (ST) at room condition. The results show that the catalysts have excellent catalytic activity in treatment of wastewater containing 10 mg/L ST, and 94% of color can be removed within 60 min. Under different cycling runs, it is shown that the catalysts are stable under such operating conditions and the leaching tests show negligible leaching effect owing to the lesser dissolution.

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Three-Dimensional Periodic Hematite Photocatalysts Fabricating by Direct Writing Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1025-1026.621 ◽

2014 ◽

Vol 1025-1026 ◽

pp. 621-627

Author(s):

Qin Mei Peng ◽

Bo Li ◽

Jin Wang ◽

Ji Jiao Li ◽

Ji Zhou

Keyword(s):

Methylene Blue ◽

Catalytic Activity ◽

Organic Contaminants ◽

Degradation Rate ◽

Sol Gel ◽

Three Dimensional ◽

High Catalytic Activity ◽

Direct Writing ◽

Catalytically Active ◽

Gel Technique

Three-dimensional (3-D) periodic hematite scaffold was successfully fabricated by direct writing method as a catalyst for degradation of organic contaminants. Photo-catalytically active α-Fe2O3 nanoparticles have been synthesized by sol-gel technique. Aqueous slurries of iron oxides were freeform fabricated to produce hematite scaffolds with a 3-D periodic architecture and multiscale porosity. The catalytic activity of the hematite scaffolds was evaluated in the degradation of Methylene Blue (MB). It was found that the degradation rate of MB dye was over 83%. The result strongly indicates that the hematite scaffolds exhibits a high catalytic activity. Moreover, this work provides an important step forward in the creation of suitable structures for photocatalyst.

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Spatial separation of protein domains is not necessary for catalytic activity or substrate binding in a xylanase

Biochemical Journal ◽

10.1042/bj2690261 ◽

1990 ◽

Vol 269 (1) ◽

pp. 261-264 ◽

Cited By ~ 55

Author(s):

L M A Ferreira ◽

A J Durrant ◽

J Hall ◽

G P Hazlewood ◽

H J Gilbert

Keyword(s):

Catalytic Activity ◽

Specific Activity ◽

Binding Capacity ◽

Spatial Separation ◽

Crystalline Cellulose ◽

Conserved Sequence ◽

Binding Domains ◽

Catalytically Active ◽

Cellulose Binding ◽

Derivatives Of

Xylanase A (XYLA) from Pseudomonas fluorescens subspecies cellulosa shows sequence conservation with two endoglucanases from the same organism. The conserved sequence in XYLA, consisting of the N-terminal 234 residues, is not essential for catalytic activity. Full-length XYLA and a fusion enzyme, consisting of the N-terminal 100 residues of XYLA linked to mature alkaline phosphatase, bound tightly to crystalline cellulose (Avicel), but not to xylan. The capacity of truncated derivatives of the xylanase to bind polysaccharides was investigated. XYLA lacking the first 13 N-terminal amino acids did not bind to cellulose. However, a catalytically active XYLA derivative (XYLA′), in which residues 100-234 were deleted, bound tightly to Avicel. Substrate specificity, cellulose-binding capacity, specific activity and Km for xylan hydrolysis were evaluated for each of the xylanases. No differences in any of these parameters were detected for the two enzymes. It is concluded that XYLA contains a cellulose-binding domain consisting of the N-terminal 100 residues which is distinct from the active site. Spatial separation of the catalytic and cellulose-binding domains is not essential for the enzyme to function normally.

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Effect of Lewis Acids on the Catalyst Activity for Alkene Metathesis, Z-/E- Selectivity and Stability of Tungsten Oxo Alkylidenes

Topics in Catalysis ◽

10.1007/s11244-021-01534-w ◽

2021 ◽

Author(s):

J. Haydée Merino ◽

Jesús Bernad ◽

Xavier Solans-Monfort

Keyword(s):

Catalytic Activity ◽

Lewis Acid ◽

Lewis Acids ◽

Heterogeneous Catalysts ◽

Catalyst Deactivation ◽

Catalyst Activity ◽

Electronic Effects ◽

Activity Increase ◽

Two Factors ◽

Hydride Elimination

AbstractLewis acids increase the catalytic activity of classical heterogeneous catalysts and molecular d0 tungsten oxo alkylidenes in a variety of olefin metathesis processes. The formation of labile adducts between the metal complex and the Lewis acid has been observed experimentally and suggested to be involved in the catalyst activity increase. In this contribution, DFT (M06) calculations have been performed to determine the role of Lewis acids on catalyst activity, Z-/E- selectivity and stability by comparing three W(E)(CHR)(2,5-dimethylpyrrolide)(O-2,6-dimesithylphenoxide) (E = oxo, imido or oxo-Lewis acid adduct) alkylidenes. Results show that the formation of the alkylidene—Lewis acid adducts influences the reactivity of tungsten oxo alkylidenes due to both steric and electronic effects. The addition of the Lewis acid on the E group increases its bulkiness and this decreases catalyst Z-selectivity. Moreover, the interaction between the oxo ligand and the Lewis acid decreases the donating ability of the former toward the metal. This is important when the oxo group has either a ligand in trans or in the same plane that is competing for the same metal d orbitals. Therefore, the weakening of oxo donating ability facilitates the cycloaddition and cycloreversion steps and it stabilizes the productive trigonal bipyramid metallacyclobutane isomer. The two factors increase the catalytic activity of the complex. The electron donating tuneability by the coordination of the Lewis acid also applies to catalyst deactivation and particularly the key β-hydride elimination step. In this process, the transition states show a ligand in pseudo trans to the oxo. Therefore, the presence of the Lewis acid decreases the Gibbs energy barrier significantly. Overall, the optimization of the E group donating ability in each step of the reaction makes tungsten oxo alkylidenes more reactive and this applies both for the catalytic activity and catalyst deactivation.

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Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

10.33774/chemrxiv-2021-d5ksj ◽

2021 ◽

Author(s):

Alexander Hill ◽

Adarsh Bhat ◽

Zachary Berquist ◽

Galen Fisher ◽

Andrej Lenert ◽

...

Keyword(s):

Catalytic Activity ◽

Catalyst Activity ◽

Core Shell ◽

Shell Nanoparticles ◽

Highly Dispersed ◽

Catalytically Active ◽

Metal Support ◽

The Stability ◽

Material Utilization ◽

Core Shell Nanoparticles

Stabilizing high dispersions of catalytically active metals is integral to improving the lifetime, activity, and material utilization of catalysts that are periodically exposed to high temperatures during operation or maintenance. We have found that annealing palladium-based core@shell catalysts in air at elevated temperature (800°C) promotes the redispersion of active metal into highly dispersed sites, which we refer to as halo sites. Here, we examine the restructuring of Pd@SiO2 and Pd@CeO2 core@shell catalysts over successive 800°C aging cycles to understand the formation, activity, nanoscale structure and stability of these palladium halo sites. While encapsulation generally improves metal utilization by providing a physical barrier that promotes redispersion over agglomeration, our cycled aging experiments demonstrate that halo sites are not stable in all catalysts. Halo sites continue to migrate in Pd@SiO2 due to poor metal-support bonding, which leads to palladium agglomeration. In contrast, halo sites formed in Pd@CeO2 remain stable. The dispersed palladium also synergistically stabilizes the ceria from agglomerating. We attribute this stability, in addition to an observed improvement in catalytic activity, to the coordination between palladium and reducible ceria that arises during the formation of halo sites. We probe the importance of ceria oxidation state on the stability of halo sites by aging Pd@CeO2 after it has been reduced. While some halo sites agglomerate, we find that returning to air aging mitigates the loss of these sites and catalytic activity. Our findings illustrate how nanoscale catalyst structures can be designed to promote the formation of highly stable and dispersed metal sites.

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Advanced sol–gel process for efficient heterogeneous ring-closing metathesis

Scientific Reports ◽

10.1038/s41598-021-92043-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Shiran Aharon ◽

Dan Meyerstein ◽

Eyal Tzur ◽

Dror Shamir ◽

Yael Albo ◽

...

Keyword(s):

Heterogeneous Catalysts ◽

Catalyst Activity ◽

Sol Gel ◽

Ring Closing Metathesis ◽

Practical Applications ◽

Sol Gel Process ◽

The Matrix ◽

Process System ◽

One Step ◽

Stage Process

AbstractOlefin metathesis, a powerful synthetic method with numerous practical applications, can be improved by developing heterogeneous catalysts that can be recycled. In this study, a single-stage process for the entrapment of ruthenium-based catalysts was developed by the sol–gel process. System effectiveness was quantified by measuring the conversion of the ring-closing metathesis reaction of the substrate diethyl diallylmalonate and the leakage of the catalysts from the matrix. The results indicate that the nature of the precursor affects pore size and catalyst activity. Moreover, matrices prepared with tetraethoxysilane at an alkaline pH exhibit a better reaction rate than in the homogenous system under certain reaction conditions. To the best of our knowledge, this is the first study to present a one-step process that is simpler and faster than the methods reported in the literature for catalyst entrapment by the sol–gel process under standard conditions.

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Precursor type affecting surface properties and catalytic activity of sulfated zirconia

Acta periodica technologica ◽

10.2298/apt0738105z ◽

2007 ◽

pp. 105-113 ◽

Cited By ~ 1

Author(s):

Aleksandra Zarubica ◽

Goran Boskovic

Keyword(s):

Catalytic Activity ◽

Beneficial Effect ◽

Surface Properties ◽

Sulfated Zirconia ◽

Tetragonal Phase ◽

Catalyst Activity ◽

Sol Gel ◽

Surface Characteristics ◽

Zirconium Hydroxide ◽

Catalytic Activities

Zirconium-hydroxide precursor samples are synthesized from Zr-hydroxide, Zr-nitrate, and Zr-alkoxide, by precipitation/impregnation, as well as by a modified sol-gel method. Precursor samples are further sulphated for the intended SO4 2- content of 4 wt.%, and calcined at 500-700oC. Differences in precursors? origin and calcination temperature induce the incorporation of SO4 2- groups into ZrO2 matrices by various mechanisms. As a result, different amounts of residual sulphates are coupled with other structural, as well as surface properties, resulting in various catalytic activities of sulphated zirconia samples. Catalyst activity and selectivity are a complex synergistic function of tetragonal phase fraction, sulphates contents, textural and surface characteristics. Superior activity of SZ of alkoxide origin can be explained by a beneficial effect of meso-pores owing to a better accommodation of coke deposits.

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Kinetic Probes of the Origin of Activity in MOF-Based C–H Oxidation Catalysts

10.26434/chemrxiv-2021-8nllf ◽

2021 ◽

Author(s):

Aishanee Sur ◽

Nicholas Jernigan ◽

David Powers

Keyword(s):

Catalytic Activity ◽

Homogeneous Catalysis ◽

Heterogeneous Catalysts ◽

Isotope Effects ◽

Catalyst Activity ◽

Oxidation Reactions ◽

Limiting Step ◽

Metal Organic ◽

Bona Fide ◽

Oxidation Chemistry

The development of homogeneous catalysis is enabled by the availability of a rich toolkit of kinetics experiments, such as the Hg-drop test, that differentiate catalytic activity at ligand-supported metal complexes from potential heterogeneous catalysts derived from decomposition of molecular species. Metal-organic frameworks (MOFs) have garnered significant attention as platforms for catalysis at site-isolated, interstitial catalyst sights. Unlike homogeneous catalysis, relatively few strategies have been advanced to evaluate the origin of catalytic activity in MOF-promoted reactions. Many of the MOFs that have been examined as potential catalysts are comprised of molecular constituents that represent viable catalysts in the absence of the extended MOF lattice, and thus interfacial sites and leached homogeneous species represent potential sources of catalyst activity. Here, we demonstrate that analysis of deuterium kinetic isotope effects (KIEs) and olefin epoxidation diastereoselectivity provides direct probes of the origin of catalytic activity in MOF-promoted oxidation reactions. These analyses support direct involvement of lattice-based Fe sites in the turnover-limiting step of C–H activation with Fe-MOF-74-based materials (i.e., the MOF functions as a bona fide catalyst) and evidence that Cu2-based MOF MIL-125-Cu2O2 functions as a solid-state initiator for solution-phase oxidation chemistry and is not involved in the turnover limiting step (i.e., the MOF does not function as a catalyst). We anticipate that the simple experiments described here will provide a valuable tool for clarifying the role of MOFs in C–H oxidation reactions.

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Nickel (II) and oxovanadium (IV) complexes supported on MCM-41 mesoporous and their application in catalytic selective sulfide and thiol oxidation

Combinatorial Chemistry & High Throughput Screening ◽

10.2174/1386207323999201111192649 ◽

2020 ◽

Vol 23 ◽

Author(s):

Mohsen Nikoorazm ◽

Maryam Khanmoradi ◽

Masoumeh Sayadian

Keyword(s):

Catalytic Activity ◽

Room Temperature ◽

Sol Gel ◽

Reaction Times ◽

Significant Loss ◽

Spectral Studies ◽

High Catalytic Activity ◽

Catalytic Systems ◽

Solvent Free Conditions ◽

Mcm 41

Introduction:: MCM-41 was synthesized using the sol-gel method. Then two new transition metal complexes of Nickel (II) and Vanadium (IV), were synthesized by immobilization of adenine (6-aminopurine) into MCM-41 mesoporous. The compounds have been characterized by XRD, TGA, SEM, AAS and FT-IR spectral studies. Using these catalysts provided an efficient and enantioselective procedure for oxidation of sulfides to sulfoxides and oxidative coupling of thiols to their corresponding disulfides using hydrogen peroxide at room temperature. Materials and Methods:: To a solution of sulfide or thiol (1 mmol) and H2O2 (5 mmol), a determined amount of the catalyst was added. The reaction mixture was stirred at room temperature for the specific time under solvent free conditions. The progress of the reaction was monitored by TLC using n-hexane: acetone (8:2). Afterwards, the catalyst was removed from the reaction mixture by centrifugation and, then, washed with dichloromethane in order to give the pure products. Results:: All the products were obtained in excellent yields and short reaction times indicating the high activity of the synthesized catalysts. Besides, the catalysts can be recovered and reused for several runs without significant loss in their catalytic activity. Conclusion:: These catalytic systems furnish the products very quickly with excellent yields and VO-6AP-MCM-41 shows high catalytic activity compared to Ni-6AP-MCM-41.

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