David Kubička

Application of Molecular Sieves in Transformations of Biomass and Biomass-Derived Feedstocks

Molecular sieves (zeolites, mesoporous materials, hierarchic systems, two-dimensional zeolites) are important acid catalysts for transformations of biomass into required products. This article covers the upgrading potential of different types of biomass based on their source and discusses the reaction pathways of their transformations emphasizing the role of molecular sieve catalysts. As typical examples, catalytic pyrolysis, deoxygenation, transesterification, dehydration, isomerization, and condensation reactions were chosen. Properties and chemical/textural characteristics of the most important molecular sieve catalysts are briefly discussed and related to their catalytic behavior in biomass transformations. Finally, potential of novel molecular sieve catalysts towards biomass upgrading is highlighted and some examples of novel zeolitic materials are addressed.

Recent Advances in Reactions of Alkylbenzenes Over Novel Zeolites: The Effects of Zeolite Structure and Morphology

Alkylbenzenes form an important segment of petrochemical industry for the manufacture of widely used commodities and specialty products. Since the last review on this topic (8), numerous new zeolite-based catalysts have been synthesized, characterized and evaluated in various transformations of aromatic hydrocarbons. This comprehensive review covers major reactions of mono-, di-, and tri-alkylbenzenes such as disproportionation, alkylation, transalkylation, isomerization, etc., over different zeolite-based acid catalysts. During the last decade, significant progress was made in the synthesis and structure determination of novel zeolites, mesoporous single crystals, hierarchic zeolites and two-dimensional zeolites. These developments have enhanced the understanding of the role of zeolites (effects of structural type, morphology, acid sites, accessibility of acid sites, shape selectivity factors) in transformations of aromatics. In this review, the emphasis is on the influence of the type of acid sites, zeolite topology, and reaction conditions on the activity, selectivity and pathways of these reactions. Thermodynamics and reaction kinetics of transformations of aromatic hydrocarbons are also discussed. This article covers mostly literature published during the period of 2002–2013.

Catalytic pyrolysis of low density polyethylene over H-β, H-Y, H-Mordenite, and H-Ferrierite zeolite catalysts: Influence of acidity and structures

Low-density polyethylene (LDPE) catalytic pyrolysis was investigated over H-β-25, H-β-150, H-β-300, H-Y-12, H-Mordenite-20, and H-Ferrierite-20 zeolite catalysts. The numbers denote the SiO2/Al2O3 molar ratios. The influence of the zeolite’s acidity on the transformation of LDPE was studied by varying the SiO2/Al2O3 molar ratios of the β zeolite. The influence of the zeolite structure was investigated by using the proton forms of Y, β, Mordenite, and Ferrierite zeolites. The catalysts were characterized using X-ray powder diffraction patterns, nitrogen adsorption, and FTIR spectroscopy with pyridine as the probe molecule. The large pore and least acidic H-β-300 catalyst showed the lowest activity in the catalytic pyrolysis of LDPE. The H-β-25 catalyst, with higher acidity than H-β-300, showed higher activity for LDPE pyrolysis than H-β-300, indicating the importance of strong acid sites for this reaction. The H-Ferrierite and H-Mordenite catalysts, with small pores, showed the lowest effect on LDPE pyrolysis, although the catalysts were more acidic than H-β-25 and H-β-150, indicating that not only acidity but also the structure and pore size of zeolites are important for pyrolysis of LDPE. However, the H-Y zeolite catalyst with large pores and cavities is not suitable for this reaction because of rapid deactivation due to coke formation.

Extra‐Large‐Pore Zeolites with UTL Topology: Control of the Catalytic Activity by Variation in the Nature of the Active Sites

The catalytic behavior of isomorphously substituted B‐, Al‐, Ga‐, and Fe‐containing extra‐large‐pore UTL zeolites was investigated in the acylation of p‐xylene with benzoyl chloride and Beckmann rearrangement of 1‐indanone oxime. The clear synergism between the Brønsted acidity (i.e., the concentration and the strength of protonic acid sites) of UTL catalysts and their activity in benzoylation was established. (Ga)UTL zeolite containing the Brønsted acid sites of medium strength is characterized by the optimum activity and selectivity in the benzoylation of p‐xylene. Because of a higher accessibility of active centers, (Al)UTL zeolite appears to be a more active and selective catalyst than (Al)BEA in the benzoylation of p‐xylene. In contrast to (B), (Ga), and (Al)UTL, the leaching of active sites occurs in the benzoylation over (Fe)UTL. All UTL zeolites showed 100 % selectivity in the Beckmann rearrangement of 1‐indanone oxime, which provides the target 3,4‐dihydroquinolin‐2(1H)‐one. (B) and (Fe)UTL zeolites containing the weakest acid centers were found to be more active in the Beckmann rearrangement of 1‐indanone oxime than (Ga) and (Al)UTL: 100 % yield of the target amide was achieved in 240 min of the reaction time over (B) and (Fe)UTL.

Towards understanding the hydrodeoxygenation pathways of furfural–acetone aldol condensation products over supported Pt catalysts

Aiming at the valorisation of furfural-derived compounds, the hydrodeoxygenation of furfural–acetone condensation products has been studied using supported platinum catalysts. The influence of the catalytic properties of different supports, such as SiO2, Al2O3, TiO2, hydrotalcite (HTC), Beta zeolite, Al-SBA-15 and WO3–ZrO2, was evaluated in a batch reactor for 480 min at 200 °C and 50 bar of H2. The used feed consisted of a mixture of furfural–acetone adducts (C8–C19), obtained in previous experiments using a continuous flow reactor and hydrotalcite as a catalyst. Except for Pt/SiO2, all catalysts showed high conversion of the reactants, especially due to the hydrogenation of all the aliphatic CC bonds. However, the extent of further hydrogenation (furan CC and ketone CO bonds) was limited, particularly when HTC and Al2O3 were used as supports. The higher accessibility of Pt/TiO2 and the smaller Pt particle size shown by Pt/Al-SBA-15, Pt/WO3–ZrO2 and Pt/Beta in comparison with the other catalysts led to an improvement in the hydrogenation of furanic and ketonic groups, likely due to lower adsorption constraints. The higher acid character of the latter group of catalysts promotes dehydration and ring opening steps, thus enhancing the selectivity towards linear alcohols. Likewise, a significant increase in the extent of aldol condensation reactions was also observed with these catalysts, yielding longer carbon chain compounds. Based on this study, a reaction scheme for the transformation of 4-(2-furyl)-3-buten-2-one (C8) into octane has been proposed in order to establish a valuable correlation between the main conversion pathways and the catalytic properties of the employed heterogeneous catalyst, thus contributing to further development of efficient deoxygenation catalysts.

On the way to improve cetane number in diesel fuels: Ring opening of decalin over Ir-modified embedded mesoporous materials

Embedded materials prepared from MCM-41 together with BE or TON were synthesized, characterized and tested in the ring opening of decalin in a temperature range of 523–623 K. The characterization results revealed that both microporous and mesoporous phases were present in the catalyst. Ir-modification did not change the phase purity, affecting, however, the acidity due to metal-support interactions. The parameters studied in ring opening of decalin were support structure, presence of Ir and temperature. The detailed analysis of 2D/3D isomers and ring opening products showed that the main ring opening products contained ethyl side chain. The Ir-modified embedded mesoporous catalysts were active and relatively selective in the ring opening of decalin, giving 35% selectivity to the ring opening products at 98% conversion at 573 K and 6 MPa.

Ring opening of decalin over Pt-and Ir-modified SAPO-5 and VPI-5 zeolite catalysts

Ring opening of decalin over Pt- and Ir-modified SAPO-5 and VPI-5 catalysts was carried in a batch reactor at 573–623 K in the presence of hydrogen. The catalysts were synthesized and characterized by using XRD, nitrogen physisorption, pyridine desorption and CO chemisorption. Bronsted acidity was essential for both isomerization and ring-opening reactions. Presence of a noble metal was found to be beneficial for isomerization and ring opening as well.

Synthesis of Pt-modified MCM-41 mesoporous molecular sieve catalysts: influence of methods of Pt introduction in MCM-41 on physico-chemical and catalytic properties for ring opening of decalin

MCM-41 mesoporous molecular sieve was modified with Pt using in-situ synthesis, ion-exchange and impregnation evaporation catalyst preparation methods. Physico-chemical properties of Pt-MCM-41 catalysts synthesized with different methods were investigated using characterization techniques such as X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray micro-analysis, X-ray photo-electron spectroscopy, pulse CO chemisorption and nitrogen adsorption. Under suitable designed synthesis conditions it was possible to introduce Pt in MCM-41 by in-situ, ion-exchange and impregnation methods without influencing the phase purity of MCM-41. The ring-opening of decalin was used as a test reaction to evaluate the catalytic properties of Pt-MCM-41 catalysts synthesized by ion-exchange, in-situ synthesis and impregnation evaporation methods. The Pt-MCM-41-IMP catalyst prepared by impregnation evaporation method was the most active in ring opening of decalin.

Aldose to ketose interconversion: galactose and arabinose isomerization over heterogeneous catalysts

Isomerization of glucose, galactose and arabinose to corresponding keto-sugars was studied in the present work over a range of heterogeneous catalysts. Magnesium aluminates with different ratios between oxides resulting in materials with a Mg/Al ratio from 0.2 to 0.9 were prepared, characterized and evaluated in terms of their catalytic behavior. The catalyst with a Mg/Al ratio close to hydrotalcites was the most efficient considering activity, selectivity and stability. The sugar structure was shown to have a minor influence on catalytic activity and selectivity.

Classification and pattern recognition of acyclic octenes based on mass spectra

Two SIMCA models were developed for the classification of acyclic octene isomers, which only form a fraction of a very complex product mixture obtained, for example, from the transformation of 1-butene. The effects of spectral transformation, namely autocorrelation and logarithmic intensity ratios transforms, and (square-root) scaling of the octane isomers mass-spectral data were investigated. Both the spectral-features preprocessing methods and scaling were found to be vital for an adequate development and improvement of the classification models. The best SIMCA models were successfully applied on gas-chromatography-mass spectroscopy (GC-MS) analysis collected from the dimerization of 1-butene over heterogeneous catalysts in the liquid phase.