Porous Silica Catalyst Research Articles

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling

AbstractCatalytic upcycling of polyolefins into high‐value chemicals represents the direction in end‐of‐life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM‐5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre‐cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1‐C7) are produced with a yield of 443 mmol gZSM‐5−1, where 74.3 % of them are C3‐C6 olefins, much superior to ZSM‐5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling.

Catalytic upcycling of polyolefins into high-value chemicals represents the direction in end-of-life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM-5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre-cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1-C7) are produced with a yield of 443 mmol gZSM-5 -1, where 74.3 % of them are C3-C6 olefins, much superior to ZSM-5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Evolution of Surface Catalytic Sites on Bimetal Silica-Based Fenton-Like Catalysts for Degradation of Dyes with Different Molecular Charges.

We present here important new findings on the direct synthesis of bimetal Cu-Mn containing porous silica catalyst and the effects of structure-directing agent removal from the prepared nanomaterial on the evolution of surface catalytic sites. The extraction-calcination procedure of the structure-directing agent removal led to the formation of Cu and Mn oxo-clusters and Cu and Mn oxide nanoparticles smaller than 5 nm, while the solely calcination procedure led to the mentioned species and in addition to the appearance of CuO nanoparticles 20 nm in size. Catalysts were tested in the Fenton-like catalytic degradation of dyes with different molecular charge (cationic, anionic, and zwitterionic) as model organic pollutants in wastewater at neutral pH. Significantly faster degradation of cationic and anionic dyes in the first 60 min was observed with the catalyst containing larger CuO nanoparticles (>20 nm) due to the less hindered generation of •OH radicals and slower obstructing of the active sites on the catalysts surface by intermediates. However, this was not found beneficial for zwitterionic dye with no adsorption on the catalysts surface, where the catalyst with smaller Cu species performed better.

One-pot direct conversion of levulinic acid into high-yield valeric acid over a highly stable bimetallic Nb-Cu/Zr-doped porous silica catalyst

The direct conversion of levulinic acid (LA) to valeric biofuel over highly-stable, non-noble metal catalyst is highly promising for the development of biorefineries.

Influence of Structure-modifying Agents in the Synthesis of Zr-doped SBA-15 Silica and Their Use as Catalysts in the Furfural Hydrogenation to Obtain High Value-added Products through the Meerwein-Ponndorf-Verley Reduction.

Zr-doped mesoporous silicas with different textural parameters have been synthesized in the presence of structure-modifying agents, and then characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at −196 °C, NH3 thermoprogrammed desorption (NH3–TPD), CO2 thermoprogrammed desorption (CO2–TPD), and X-ray photoelectron spectroscopy (XPS). These porous materials were evaluated in the furfural hydrogenation through the Meerwein-Ponndorf-Verley (MPV) reaction. The catalytic results indicate that the catalyst synthesized under hydrothermal conditions and adding a pore expander agent is more active and selective to furfuryl alcohol. However, the Zr-doped porous silica catalysts that were synthesized at room temperature, which possess narrow pore sizes, tend to form i-propyl furfuryl and difurfuryl ethers, coming from etherification between furfuryl alcohol (FOL) and isopropanol molecules (used as H-donor) by a SN2 mechanism.

Hydrogen and carbon allotrope production through methane cracking over Ni/bimodal porous silica catalyst: Effect of nickel precursor

Nickel-based catalyst is highly active for hydrogen production through methane cracking reaction at moderate reaction temperature. However, Ni catalyst is easily deactivated by carbon encapsulation. In order to solve this problem, this research studies the effect of nickel precursors—nickel acetate (NA), nickel carbonate (NC) and nickel nitrate (NN)—on the activity and stability of nickel/bimodal porous silica (Ni/BPS) catalyst in methane cracking reaction. It was found that these nickel precursor solutions had different pH values, resulting in different interactions between surface silanol groups of BPS supports and Ni. Among these catalysts, Ni(NC)/BPS catalyst exhibited high nickel dispersion and weak interaction between Ni and BPS support; it then gave the highest CH4 conversion and better stability compared to the other catalysts. In addition, H2 yield of Ni(NC)/BPS catalyst was 2.90 and 1.40 times higher than those of Ni(NA)/BPS and Ni(NN)/BPS catalysts, respectively. Moreover, carbon nanofibers were grown in Ni(NC)/BPS and Ni(NN)/BPS catalysts, whereas carbon nanotubes were formed on Ni(NA)/BPS catalyst, due to the different nickel particle sizes, dispersions, and Ni—BPS support interactions.

Highly active and selective Ti-incorporated porous silica catalysts derived from grafting of titanium(iv)acetylacetonate

Ti(iv)acetylacetonate-grafted porous silicas showed high catalytic activities for the epoxidations of cyclohexene and limonene with tert-butyl hydroperoxide as an oxidant.

Biodiesel production from transesterification of palm oil with methanol over CaO supported on bimodal meso-macroporous silica catalyst

Calcium oxide-loaded porous materials have shown promise as catalysts in transesterification. However, the slow diffusion of bulky triglycerides through the pores limited the activity of calcium oxide (CaO). In this work, bimodal meso-macroporous silica was used as a support to enhance the accessibility of the CaO dispersed inside the pores. Unimodal porous silica having the identical mesopore diameter was employed for the purpose of comparison. Effects of CaO content and catalyst pellet size on the yield of fatty acid methyl esters (FAME) were investigated. The basic strength was found to increase with increasing the CaO content. The CaO-loaded bimodal porous silica catalyst with the pellet size of 325μm achieved a high %FAME of 94.15 in the first cycle, and retained an excellent %FAME of 88.87 after five consecutive cycles.

Synthesis of hierarchically porous silicas with mesophase transformations in a four-component microemulsion-type system and the catalytic performance for dibenzothiophene hydrodesulfurization

Hierarchical porous materials especially the silica-based ones are undergoing rapid development due to potential applications in the fields of catalysis, adsorption, separation, and biomedical processes. Although various synthesis methods involving emulsions, colloids, and surfactants have been reported, synthesis of hierarchical porous silicas (HPS) with complex mesophase transformations by using a four-component microemulsion (surfactant/cosurfactant/oil/water) templating approach is still challenging. Herein, we have successfully synthesized porous silica materials by introducing n-butanol (Bu) as the cosurfactant and 1,3,5-trimethylbenzene (TMB) as the oil component in a four-component P123–n-butanol–1,3,5-trimethylbenzene–water system. By simply increasing the molar ratio of Bu to TMB continuously while keeping a fixed mass of TMB in the mean time, mesophase transformations, progressing from mesocellular foam (MCF) via a vesicle-like structure to an ordered 2D hexagonal structure (SBA-15), can be observed. Moreover, an opposite phase transformation process was also proved by gradually increasing the molar ratio of TMB to Bu by maintaining a certain value for the Bu content in the initial system. All the mixed phase silica materials including hexagonal–vesicle, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type show hierarchically porous structures. The mechanism for the mesophase transformation was proposed and a micelle/microemulsion method with bimodal templates was put forward to form hierarchical porous silicas with a mixed phase of the MCF–disordered-SBA-15-type structure. Furthermore, a series of Al-containing mesoporous silicas with different structures (hexagonal, vesicle, MCF, MCF–vesicle–hexagonal, and MCF–disordered-SBA-15-type) were used as catalyst supports for dibenzothiophene hydrodesulfurization. The NiMo/Al-hierarchical porous silica catalyst with pore structures of MCF–disordered-SBA-15-type displayed the best hydrodesulfurization performance among all the studied catalysts.

Highly accessible catalytic sites on recyclable organosilane-functionalized magnetic nanoparticles: An alternative to functionalized porous silica catalysts

Diaminosilane-functionalized cobalt spinel ferrite (CoFe 2O 4) magnetic nanoparticles are synthesized and used as efficient heterogeneous base catalysts for the Knoevenagel condensation of aromatic and heteroaromatic aldehydes with malononitrile. The magnetic nanoparticle catalyst is characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and nitrogen physisorption measurements. Quantitative conversion of the reactants is achieved under mild conditions. Recovery of the catalyst is easily achieved by magnetic decantation. The supported catalyst is reused five times without significant degradation in catalytic activity. No contribution from homogeneous catalysis due to active amine species leaching into reaction solution is detected. The performance of the magnetic base catalyst in the Knoevenagel reaction is directly compared with diamine-functionalized SBA-15 and MCM-48. Reaction rates over the non-porous, magnetic nanoparticle catalyst are comparable to the large pore mesoporous silica materials and faster than the small pore MCM-48 material with ∼22 Å diameter pores. A significant effect of the acidity of the magnetic nanoparticle support on catalyst activity in the Knoevenagel condensation is also observed.

Preparation of Functionalized Porous Silica by Ultrasonic Technique for the Methylation Reaction of Phenol with Dimethyl Carbonate

AbstractPorous silica modified with (CH2)3NH2 (primary amine), (CH2)3NHCH2CH2NH2 (secondary/primary amine) and (CH2)3N‐cycl‐(CH2)4 (tertiary amine) were synthesized by ultrasonic technique under mild conditions. The samples were characterized by BET, elemental analysis and TG, showing that the organosilane moieties were grafted onto the surface of porous silica by covalent bond. The structure of the organosilane moieties and ultrasonic treatment time were all significant for the quantities of grafted amino groups. The samples exhibited promising catalytic properties towards the methylation reaction of phenol with dimethyl carbonate (DMC). The methylation reaction with the modified samples featured high selectivity at high conversion. The samples were subjected to utilization for a few recycles without obvious loss of activity to indicate that ultrasonic technique was effective for the preparation of organically modified porous silica catalysts.

Nickel supported on porous silica as catalysts for the gas-phase hydrogenation of acetonitrile

A series of nickel supported on different porous silica catalysts (5 wt% Ni) were prepared by incipient wetness impregnation. The catalysts were characterized by XRD, H 2-TPR, N 2 adsorption at 77 K, chemisorption of H 2, and IR spectroscopy after CO and CH 3CN adsorption. Preliminary experiments have shown that the choice of nickel citrate instead of nickel nitrate as impregnation salt allows high degrees of nickel dispersion to be obtained. The catalytic behavior of this family of nickel-based catalysts reveals that the acid–basic properties of support seem to be more crucial than the extent of specific surface area and the metal particle size in determining the catalytic behavior. Thus, when nickel is supported on less acidic supports, the formation of higher amines (diethylamine and triethylamine) by condensation reactions is negligible, and full acetonitrile conversion and yields of ethylamine higher than 80 mol% at 408 K are reached.

High temperature effects on the dense phase properties of gas fluidized beds

This paper reports some of the results obtained from an extensive experimental campaign aimed to study the influence of temperature on the fluidization behaviour of solid materials. The fluidization behaviour of a wide range of materials was investigated from ambient conditions up to 650°C. The aim of this work was to highlight the conditions under which the role of the hydrodynamic forces (HDFs) or interparticle forces (IPFs) were dominant, in order to make predictable the fluidization behaviour at elevated temperatures. To this end, the fluidization behaviour of three fresh FCC catalysts was studied. An E-cat FCC catalyst, which contained process residuals, was examined without performing pre-treatments prior to fluidization tests. Furthermore, a highly porous silica catalyst was doped with increasing amount of potassium acetate (KOAc), 1.7, 7 and 10 wt.%, and a sample of glass ballotini was doped with 0.1 wt.% of KOAc. This was done in the attempt of modifying their surface characteristics, thus triggering changes in their fluidization behaviour with increasing temperature. The measured pressure drop across the bed and deaeration tests was used to highlight changes in the fluidization behaviour as a function of temperature. The standardized collapse time (SCT) was obtained from the collapse profiles and was used to distinguish between systems of powders dominated by HDFs and IPFs. Results obtained from analytical techniques such as thermomechanical analysis (TMA), Gas Chromatography Mass Spectrometry analysis (GCMS) and scanning electron microscope (SEM) are also discussed, these techniques were used to investigate physical changes in the particles with increasing temperature.

Leaching of amorphous V- and Ti-containing porous silica catalysts in liquid phase oxidation reactions

The extent and effects of leaching of amorphous microporous and mesoporous V- and Ti-containing silica catalysts during selective oxidation reactions with t-butyl hydroperoxide and hydrogen peroxide have been investigated under aqueous and water free reaction conditions. Nanoparticles of catalyst were found to obscure the analysis of the nature of the reactions. These particles, present in all experiments, cannot be removed by filtration or centrifuging and falsely contribute to apparent leaching. With the V-containing materials leaching leads to homogeneous V-species, which at least contribute, in all cases studied, to the overall reactivity. True leaching contributions are dependent on solvent, substrate and oxidant, and therefore, cannot be generalized. With the Ti-containing catalysts leaching is strongly dependent on reaction conditions.

ChemInform Abstract: A New Method for Evaluating the Inner Pore Structure of Porous Catalysts‐Resin Replication of Silica.

In this note, the authors present SEM images of the shapes of a porous silica catalyst support observed by a new resin replication which had been successfully adopted for the visualization of pore structures of porous aluminum electrodes

A new method for evaluating the inner pore structure of porous catalysts—Resin replication of silica

In this note, the authors present SEM images of the shapes of a porous silica catalyst support observed by a new resin replication which had been successfully adopted for the visualization of pore structures of porous aluminum electrodes