Nanostructured catalytic films for multiphase microstructured reactors

The application of microstructured catalytic reactors for gas-liquid reactions requires the development of new techniques for the incorporation of highly active catalytic thin films onto their microstructured surfaces. These catalytic thin films may have open porosities even up to 50%. Their application limits the pressure drop over the microreactor in comparison to micro packed beds, it enhances the catalyst accessibility, and it may significantly reduce mass transfer limitations. In this PhD thesis, ordered mesoporous silica and titania films with a thickness of 100 to 400 nm were developed via an evaporation induced self assembly method on different substrates (glass, silicon, titanium). These polymer templated meso¬porous silica films have a narrow pore size distribution and were synthesized with a wide range of pore sizes (2 to 8 nm). A new calcination protocol was developed which allows the complete removal of the surfactant at mild conditions. The thermal and hydro¬thermal stability of the films that were obtained with an ionic surfactant was improved by pH adjust¬ment during hydrolysis and by Al incorporation. Microwave assisted hydro¬thermal synthesis of these ordered microporous films was also investigated in an attempt to reduce the synthesis time from several days to less than 10 hours. The obtained thin films have been loaded with polymetallic nanoparticles with a size of 1 to 3 nm to specifically activate a selected functionality of complex organic molecules. Methods for the deposition and the stabilization of bi-metallic and tri-metallic clusters by adsorption onto the mesoporous thin films have been investigated. A "one pot" sol-gel synthesis of the mesoporous films with embedded colloidal nano¬particles was developed which eliminates an additional impregnation step and produces a uniform distribution of the active components throughout the mesoporous films. Various experimental techniques such as ellipsometric porosimetry, XRD, 2D SAXS, XPS, SEM, and TEM have been applied to obtain insight in the physical and chemical phenomena that determine the performance as well as the stability of the thin films. The activity and the selectivity of the resulting catalytic thin films have been investigated in the batch and in the continuous mode in the hydrogenation of citral and phenylacetylene. The latter was done in a 10 m long micro capillary (i.d. 250 µm) with a catalytic thin film deposited onto its inner channel wall surface. It was shown that the selectivity towards the target product can be changed by varying the metal ratio in the bimetallic nanoparticles. The high stability of these catalytic thin films allows their further implementation in fine chemicals synthesis using microstructured reactors

Glycerol to solketal for fuel additive: Recent progress in heterogeneous catalysts

© 2019 by the authors. Biodiesel has been successfully commercialized in numerous countries. Glycerol, as a byproduct in biodiesel production plant, has been explored recently for fuel additive production. One of the most prospective fuel additives is solketal, which is produced from glycerol and acetone via an acetalization reaction. This manuscript reviewed recent progress on heterogeneous catalysts used in the exploratory stage of glycerol conversion to solketal. The effects of acidity strength, hydrophobicity, confinement effect, and others are discussed to find the most critical parameters to design better catalysts for solketal production. Among the heterogeneous catalysts, resins, hierarchical zeolites, mesoporous silica materials, and clays have been explored as effective catalysts for acetalization of glycerol. Challenges with each popular catalytic material are elaborated. Future works on glycerol to solketal will be improved by considering the stability of the catalysts in the presence of water as a byproduct. The presence of water and salt in the feed is certainly destructive to the activity and the stability of the catalysts

Film properties and in-situ optical analysis of TiO2 layers synthesized by remote plasma ALD

TiO2 is a widely studied material due to its optical and photocatalytic properties and its hydrophilic nature after prolonged UV exposure. When synthesized by atomic layer deposition (ALD) the TiO2 can be deposited with ultimate growth control with a high conformality on demanding topologies and even at room temperature when e.g. using a plasma based process. We report on the deposition of TiO2 films using remote plasma ALD with titanium (IV) isopropoxide as precursor and O2 plasma as oxidant. Stochiometric TiO2 films with carbon and hydrogen levels below the detection limit of Rutherford backscattering/elastic recoil detection (<2 at.%) have been deposited within the temperature range of 25°C to 300°C. Depending on the ALD conditions and film thickness amorphous films turn anatase for temperatures higher than 200°C as revealed by X-ray diffraction. It is demonstrated that this change in crystal phase can also be observed by spectroscopic ellipsometry revealing an increase in growth rate per cycle (from typically 0.45 Å/cycle to 0.7 Å/cycle) and change in bandgap (from 3.4 eV to 3.7 eV) when the TiO2 becomes anatase. An accompanying change in surface topology is clearly observed by atomic force microscopy. The hydrophilicity of low temperature TiO2 films is studied by contact angle measurements for adhesion purposes revealing that the amorphous films are super-hydrophilic after UV exposure

Citral hydrogenation over Pt loaded micro- and mesoporous supports : the interplay between steric limitations and acidity

The effect of pore morphology and acidity on the selectivity in the hydrogenation of citral was investigated on a series of bifunctional catalysts: Pt-H-SAPO-5, Pt-H-Y zeolite, and Pt-H-MCM-41. The reaction was studied in a batch reactor at 70oC with 10 bar total pressure. The highest selectivity to the unsaturated alcohols of 57% was obtained on the Pt-H-SAPO-5 catalyst at a conversion of 46%. The interplay among a monodimensional pore channel of the H-SAPO-5 support, weak Br?nsted acidity of this silicoaluminophosphate, and large platinum nanoparticles contributed to a high selectivity. The corresponding turn over frequency was 0.036 s-1. Pt-H-MCM-41 showed the highest selectivity to menthol as by product, while Pt-H-Y zeolite demonstrated the highest dehydration rate

Stability Assessment of Regenerated Hierarchical ZSM-48 Zeolite Designed by Post-Synthesis Treatment for Catalytic Cracking of Light Naphtha

Hierarchical ZSM-48, a one-dimensional pore system zeolite with the presence of mesopores, was obtained by post-synthesis alkaline and acid treatments. Hierarchical ZSM-48 exhibited excellent hexane cracking activity compared to parent ZSM-48, which can be attributed to better diffusion as a result of the created mesoporosity. Moreover, the post-synthesis treatment allowed for manipulation of the distribution of active sites. Consequently, better stability and higher propylene selectivity were accomplished. The spent catalyst was regenerated by removing the deposited coke from the pores, and the regenerated catalyst was characterized again to investigate the recyclability of the hierarchical structure achieved. Parent ZSM-48 showed the same textural and acidic properties after regeneration, while the structure of the post-treated sample suffered from serious defects. The defects severely decreased the number of active sites as measured by pyridine Fourier transform infrared spectroscopy and caused major structural collapse as observed by scanning electron microscopy and transmission electron microscopy

Recent Progress in Low-Cost Catalysts for Pyrolysis of Plastic Waste to Fuels

The catalytic and thermal decomposition of plastic waste to fuels over low-cost catalysts like zeolite, clay, and bimetallic material is highlighted. In this paper, several relevant studies are examined, specifically the effects of each type of catalyst used on the characteristics and product distribution of the produced products. The type of catalyst plays an important role in the decomposition of plastic waste and the characteristics of the oil yields and quality. In addition, the quality and yield of the oil products depend on several factors such as (i) the operating temperature, (ii) the ratio of plastic waste and catalyst, and (iii) the type of reactor. The development of low-cost catalysts is revisited for designing better and effective materials for plastic solid waste (PSW) conversion to oil/bio-oil products

Opportunities for less-explored zeolitic materials in the syngas-to-olefins pathway over nanoarchitectured catalysts: a mini review

The continuous demand for olefins has stimulated recent research to develop appropriate technology to produce olefins from alternative resources. Syngas-to-olefins (STO) is considered to be a promising pathway due to the availability of numerous technologies to produce syngas from municipal solid waste and biomass. The development of catalysts to obtain high CO conversion and high selectivity to olefins is still in progress. The first route is based on iron and cobalt catalysts via Fischer Tropsch synthesis to olefins (FTO) with a range of promising supports and promoters. The second approach is based on metal oxide-zeolite (OX-ZEO) composites, with a focus on combined metal oxides to increase the CO conversion. Finally, the potency of less-explored zeolite frameworks such as FER, KFI and Rho zeolites is highlighted. We propose that researchers should focus on FER, KFI and Rho zeolites. However, further reaction mechanism studies should be elaborated to obtain their optimum conditions for STO

Enhancement of the stability of micro porous silica films in non-aqueous solvents at elevated temperatures

The long-order structure of micro porous silica thin films, deposited on Si substrates was improved by pH adjustment of the synthesis mixture to 2.0 during the hydrolysis of TEOS. It was further improved by incorporation of Al at an Al/Si ratio of 0.005. After exposure to non-polar solvents, the long-order structure was still present after 48 hours. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was tested in the hydrogenation of phenyl acetylene perfonued over 1 wt% Pd/Si(Al)02/Si (A1/Si=0.007) films at 30 ‘C and 10 bar H2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs

Enhancement of the stability of microporous silica films in non-aqueous solvents at elevated temperature

The effect of Al incorporation and pH adjustment during hydrolysis of the silica precursor on the thermal and structural stability of ordered microporous silica films with a 2D structure is presented. The structural stability of the films was determined from a combination of LA XRD/TEM data with porosity data obtained from ethanol adsorption isotherms. Thermogravimetric analysis and FTIR data were used to determine the template removal and the thermal stability. Stability of aluminium incorporated silica films has further been examined in several organic solvents with different polarity. A solvent with a higher polarity interacts more strongly with the films; the long-order structure disappeared after exposure to polar solvents. After exposure to non-polar solvents, the pore size uniformity was retained after 48 h. The samples with an Al/Si ratio of 0.007 showed the smallest d-spacing shift after exposure to hexane. The stability was further tested in the hydrogenation of phenylacetylene performed in a batch reactor over 1 wt.% Pd/Si(Al)O2/Si (Al/Si = 0.007) films at 30 °C and 10 bar H2 with hexane as solvent. No deactivation was observed in two subsequent hydrogenation runs. © 2009 Elsevier Inc. All rights reserved