Bifunctional Zeolite Catalysts Research Articles

Elucidating and Controlling Reaction Pathways for 2-Methylfuran Aromatization Using Bifunctional Zeolite Catalysts

Elucidating and Controlling Reaction Pathways for 2-Methylfuran Aromatization Using Bifunctional Zeolite Catalysts

One-pot conversion of α-pinene into biomass high energy density fuel over a bifunctional zeolite catalyst

A shape-selective bifunctional catalyst (Rux/SOT-Hβ) was furnished by loading Ru onto the Hβ zeolite prepared via seed organic template (SOT) method using the seeds obtained via steam-assisted conversion (SAC) method. The Rux/SOT-Hβ catalyst exhibited both favorable acid-catalytic performance and hydrogenation performance in the two-stage one-pot conversion of α-pinene, enabling an energy-efficient process for producing biomass blended high energy density fuels (HEDF). The effect of preparation conditions of Hβ zeolite carrier, metal type, loading amount, and loading method on the catalytic performance of the bifunctional catalyst was investigated. After the optimization of the catalytic process over Ru1.2/SOT-Hβ using pinane as the reaction medium, the resulting liquid reaction mixture without undergoing further distillation and other operations was found to possess good biomass HEDF properties. Feasible recyclability of Ru1.2/SOT-Hβ catalyst in α-pinene one-pot conversion was also demonstrated by a 3-run recycling test.

Small-sized Ni nanoparticles embedded nickel phyllosilicate as a metal-acid bifunctional zeolite catalyst for cooperatively boosting CO2-CH4 reforming

Ni-based catalysts using siliceous materials as the supports have suffered from two challenging issues of sintering and carbon deposition for dry reforming of methane (DRM), resulted from a weak metal-support interaction. Given these, a novel metal–acid bifunctional Ni@S-1 zeolite catalyst is tailored from the evolution of hydroxylated nickel phyllosilicates that are formed by subtly controlling the coordination environments of Ni precursor complexes in the silicalite-1 (S-1) zeolite. The developed Ni0.44@S-1 catalyst renders almost equivalent CH4 and CO2 conversions (85.1 % and 88.7 %), high H2/CO molar ratio (about 1) and superb long-term stability during 100 h with no activity loss at 750 °C with a WHSV of 100 L·gcat−1·h−1, outperforming other control catalysts under investigation. Such superior catalytic behavior benefits from the synergy between highly uniform Ni nanoparticles (3–5 nm) confined in the micropores of zeolite and substantially formed Lewis acid sites due to coordinatively unsaturated Ni2+ sites located at the reduced 2:1 nickel phyllosilicate, as revealed by detailed characterizations. Meanwhile, it further discloses that a benign balance between formation and elimination of “process carbon” species is responsible for improving the carbon resistance of catalyst during the DRM reaction. The present design broadens a new insight for the development of new Ni-based catalysts with simultaneous coking- and sintering-resistant for the DRM application.

A highly efficient bi-functional zeolite catalyst for low temperature catalytic cracking of n-octane to produce propylene: Joint contribution of nanogold and dealumination

With respect to catalysis, the pursuit of low reaction temperatures has received continuous efforts for developing energy efficient and environmentally friendly processes. In this study, the significant promotion in the catalytic cracking performance of n-octane at low temperatures of 260–460 °C over Au/ZSM-5 catalysts was obtained via the joint contribution of dealumination and Au species. A 63.5% propylene selectivity and 100% n-octane conversion were obtained over the optimized catalyst at 410 °C. The higher propylene yield was attributed to an increase in the concentration of Brønsted acids and a decrease in that of Lewis acids, as well as synergy between acid sites and Au species. The positive effect of Au species during dehydrogenation at lower temperatures was verified, and electron transfer from Au to the zeolite framework was proposed.

Chemical Conversion of Fischer–Tropsch Waxes and Plastic Waste Pyrolysis Condensate to Lubricating Oil and Potential Steam Cracker Feedstocks

The global economy and its production chains must move away from petroleum-based products, to achieve this goal, alternative carbon feedstocks need to be established. One area of concern is sustainable production of synthetic lubricants. A lubricating oil can be described as a high boiling point (>340 °C) liquid with solidification at least below room temperature. Historically, many lubricants have been produced from petroleum waxes via solvent or catalytic dewaxing. In this study, catalytic dewaxing was applied to potential climate neutral feedstocks. One lubricant was produced via Fischer–Tropsch (FT) synthesis and the other lubricant resulted from low temperature pyrolysis of agricultural waste plastics. The waxes were chosen because they each represented a sustainable alternative towards petroleum, i.e., FT waxes are contrivable from biomass and CO2 by means of gasification and Power-to-X technology. The pyrolysis of plastic is a promising process to complement existing recycling processes and to reduce environmental pollution. Changes in cloud point, viscosity, and yield were investigated. A bifunctional zeolite catalyst (SAPO-11) loaded with 0.3 wt% platinum was used. The plastic waste lubricants showed lower cloud points and increased temperature stability as compared with lubricants from FT waxes. There was a special focus on the composition of the naphtha, which accumulated during cracking. While the plastic waste produced higher amounts of naphtha, its composition was quite similar to those from FT waxes, with the notable exception of a higher naphthene content.

One-step synthesis of bi-functional zeolite catalyst with highly exposed octahedral Co for efficient epoxidation of bulky cycloalkenes

Bi-functional zeolite catalyst, incorporated with both organic groups and transition metal ions, has been firstly one-step synthesized by dry gel conversion method, which is characterized by powder XRD, solid-state 27Al, 29Si, 13C MAS NMR, FT-IR, Raman, UV–vis, X-ray photoelectron spectroscopy, and so on. Notably, the SiO/SiI ratio in the synthesis gel has important influence on the coordination state and distribution of cobalt species in the hybrid zeolite. Low SiO/SiI ratio has accelerated the formation of hybrid zeolite with tetrahedral framework cobalt while high SiO/SiI ratio has accelerated the additional assembly of hybrid zeolite with octahedral extra-framework cobalt. In the catalytic epoxidation of bulky cycloalkenes with air, hybrid zeolite with both tetrahedral framework cobalt and octahedral extra-framework cobalt shows the most excellent catalytic performance and TON value, compared with pure inorganic zeolite, hybrid zeolites with only tetrahedral framework cobalt species, and hybrid zeolites with Co species introduced by ion-exchange or wet impregnation methods, which is ascribed to the synergistic roles of organic groups and cobalt species. On one hand, the highly exposed octahedral extra-framework cobalt species act as an efficient supplement of tetrahedral framework cobalt, and the interactions of accessible catalytic active sites with bulky cycloalkene molecules have been strengthened greatly. On the other hand, mercaptopropyl groups are beneficial for the formation of stable heterogeneous catalyst with lipophilic surface through anchoring the extra-framework cobalt species and modifying the surface of the zeolite, which accelerate the epoxidation reaction efficiently.

Creation of gallium acid and platinum metal sites in bifunctional zeolite hydroisomerization and hydrocracking catalysts by atomic layer deposition

Active sites in bifunctional zeolite catalysts were engineered using atomic layer deposition (ALD). Gallium acid and platinum metal sites were introduced to zeolites via ALD and investigated for a hydroconversion reaction.

Cascade reaction engineering on zirconia-supported mesoporous MFI zeolites with tunable Lewis-Brønsted acid sites: a case of the one-pot conversion of furfural to γ-valerolactone.

Catalytic cascade reactions are strongly desired as a potential means of combining multistep reactions into a single catalytic reactor. Appropriate catalysts composed of multi-reactive sites to catalyze cascade reactions in a sequential fashion are central to such efforts. Here, we demonstrate a bifunctional zeolite catalyst with close proximity of Brønsted and Lewis acid sites through the synthesis of a mesoporous ZrO2[Al]MFI nanosponge (NS). The unique mesopores of the MFI-NS allow the confinement of zirconium oxide clusters (Lewis acid sites, LA) within the few-unit-cell-thin MFI aluminosilicate zeolite wall (Brønsted acid sites, BA). Such a structure is clearly distinct from the conventional MFI zeolite, where the agglomeration of zirconium oxide clusters onto the external surface area within the crystal bulk is not possible, resulting in segregated BA and LA sites on the internal and external zeolite, respectively. By bringing the BA and LA within ZrO2[Al]MFI-NS 30, we uncovered a more efficient catalytic route for the conversion of furfural (100% within 2 h) to γ-valerolactone (GVL) (83%). This route is only evident when the long molecular diffusion path, in the most extreme case of physically mixed ZrO2-(LA) and Al-zeolites (BA) (45% of GVL yield), is eliminated. Unlike the bifunctional ZrO2–Al-beta (GVL yield of 75%), where the BA concentration is greatly compromised at the expense of LA formation, we also show that the ZrO2[Al]MFI-NS is able to maintain a high density and good stability of both types of acids.

Hydrocracking of hydrotreated light cycle oil to mono aromatics over non-noble bi-functional (ni-w supported) zeolite catalysts

The bi-functional catalysts comprising non-noble metals such as Ni-W supported on zeolites were prepared to study hydrocracking of hydrotreated Light Cycle Oil (LCO) conversion into mono-aromatics. The three Ni-W supported zeolite catalysts with mixture of Y and Beta (Catalyst-A), Y (Catalyst-B), and Beta zeolites (Catalyst-C) were prepared by wetness impregnation method and characterized by using different techniques to understand the physico-chemical properties. The characterization results indicated that Ni-W supported on Beta zeolite catalyst has higher overall acidity and strong interaction between the H2W12O40 and Ni2+ ions than Ni-W supported on mixture of Y & Beta, and Y zeolites. Furthermore, Beta zeolite catalyst exhibited tetrahedral tungstate species, which are due to strong interaction between support and metal ions. Among these catalysts, Ni-W supported on Beta zeolite catalyst showed high conversion for mono-aromatic 2 ring, and di-aromatics and selectivity towards mono-aromatics (43.5%). The high conversion of this catalyst could be due to higher total acidity and the presence of tetragonal tungsten species. High selectivity of mono-aromatics may be due to larger average pore diameter of the Beta zeolite.

Catalyzing the Hydrocracking of Low Density Polyethylene

The hydrocracking of squalane and low density polyethylene (LDPE) into low molecular weight hydrocarbons has been demonstrated with the use of bifunctional zeolite catalysts, Pt-impregnated USY and...

Heavy naphtha upgrading by catalytic reforming over novel bi-functional zeolite catalyst

Naphtha catalytic reforming process using bimetallic platinum and titanium loaded on nano synthesized HY zeolite was investigated for the product octane number enhancement. The activity of five samples of the prepared catalyst with different bimetallic loading of 0.13, 0.25 wt% Pt and 0.75, 1, 2.2 wt% Ti were investigated for Iraqi heavy naphtha catalytic reforming at the temperature range of 490, 500 and 510 °C and pressure of 10 bar in a packed bed pilot plant reactor. The best result of the research octane number was 84 for reformate product using the sample of 0.13% Pt–0.75% Ti%/HY zeolite at temperature 510 °C and 10 bar achieving 47% increase. All samples of the prepared catalyst showed a good stability during the operation at severe conditions and the maximum carbon content was about 9% due to the deposition of coke precursor on the catalyst surface. The reformate yield was investigated for all catalyst samples under 10 and 20 bars and the same range of temperature and ranged from 89 to 94%. These results are encouraging for future possible replacement of the conventional catalyst by the local synthetic zeolite. Octane number was correlated on the basis of constituent’s boiling points. The maximum absolute error between the experimental and predicted octane number was about 3 and 5% using 10 and 20 bar respectively.

Reductive splitting of hemicellulose with stable ruthenium-loaded USY zeolites

Precisely balancing of the location, amount and strength of the acid and metal function on a bifunctional zeolite catalyst is essential for selective sugar alcohol formation.

Hydroisomerization and hydrocracking of linear and multibranched long model alkanes on hierarchical Pt/ZSM-22 zeolite

Hydroisomerization and hydrocracking using bifunctional zeolite catalysts with hydrogenation-dehydrogenation next to the Brønsted acid functionality are at the heart of key refinery processes converting heavy petroleum fractions to high grade lubricants and fuels. Hierarchical zeolites presenting a network of auxiliary mesoporosity in addition to their native microporosity are known to improve accessibility to their active sites. In this paper we assess the impact of hierarchization by demetallation of the well-established hydroisomerization catalyst Pt/ZSM-22 on the reaction pathways of the n-decane, n-nonadecane and pristane (2,6,10,14-tetramethylpentadecane) model molecules. Detailed analysis of reaction products and assessment of acid site accessibility in conventional and hierarchical ZSM-22 samples highlight the contributions of acid sites in pore mouths and micropores to the skeletal rearrangement and cracking reactions.

Effect of Noble Metals on the Strength of Brønsted Acid Sites in Bifunctional Zeolites

Abstract1H magic angle spinning (MAS) NMR and FTIR spectroscopy with deuterated acetonitrile and pyridine as probe molecules, respectively, were used to study the strength of Brønsted acid sites in Pt‐ and Ir‐modified zeolites Y and Beta in comparison with the materials in their H,Na forms. For both types of zeolites, the following sequence of the acid strengths was found: zeolites in their H,Na form>Pt‐modified zeolites>Ir‐modified zeolites. As the 1H MAS NMR signals of the bridging OH groups (Si(OH)Al) in the noble‐metal‐modified zeolites have the same spectroscopic properties as those observed in the materials in the H,Na forms, no direct influence of the noble metals on the nature of the hydroxyl protons or on the local structure of Si(OH)Al groups is expected. However, it is suggested that noble metals in these bifunctional zeolite catalysts are involved in charge transfer with neighboring framework atoms, which affects the mean framework electronegativity of the zeolites under study. This effect causes a variation of the acid strength of the Si(OH)Al groups similar to that observed for zeolites with different framework Al contents.

Hydrogenolysis of hydroxymatairesinol on Y derived catalysts: A computational study

Hydrogenolysis of 7-hydroxymatairesinol (HMR) to matairesinol (MAT) occurs on palladium supported acidic catalysts. HMR has three stereochemical centres and naturally exists as a mixture of two diastereoisomers, namely RRR-HMR and SRR-HMR. The latter is significantly more reactive than the former, in the reaction above. In order to elucidate the hydrogenolysis mechanism, simple surface events involving HMR derivatives on aluminated faujasite (H-Y) fragments were simulated by quantum chemical calculations. The metallic function of a Pd/H-Y acidic catalyst was also mimicked by a minimal palladium cluster. Stereochemical evidences pointed already out that water β-elimination on the epimeric centre, leading to an olefinic intermediate, should mainly occur for the adsorbed SRR-HMR stereoisomer. As a consequence, it was hypothesized that this feature could explain the different reactivity of the RRR-HMR and SRR-HMR hydrogenolysis, occurring on metal supported bi-functional zeolite catalysts. The significance of this inference is decreased by the here study. Finally, it is demonstrated that several HMR to MAT reaction paths may coexist and that the metal component of the Pd/H-Y bi-functional catalyst cannot be involved in steps discriminating for the whole reaction rate and selectivity.

A kinetic study of benzene alkylation with ethane into ethylbenzene over bifunctional PtH-MFI catalyst

Benzene alkylation with ethane into ethylbenzene (EB) was studied at 370 °C over a PtH-MFI bifunctional catalyst of high acidity (Si/Al = 15). Highly selective and stable catalyst operation was observed at benzene conversions up to 10–12%, which are close to the thermodynamic equilibrium conversion value of 13.5%. Kinetic analysis of the experimental data reveals that EB is formed via two consecutive reaction steps: (i) ethane dehydrogenation into ethene over Pt sites and (ii) benzene alkylation with ethene over acid sites. These reactions dominate at low contact times and benzene conversions up to 10-12%. At higher conversions (i.e. higher contact times) other reactions start to compete with the EB formation steps leading to a steep drop in the EB selectivity and to a decrease in the catalyst stability. The analysis of these side reactions results in a better understanding of the requirements for the selective and stable benzene alkylation with ethane into EB over bifunctional zeolite catalysts.

Hydroisomerization of ethylbenzene over bimetallic bifunctional zeolite catalysts

Zeolite-β and mordenite were impregnated with 0.1 wt.% Pt and varying (0, 0.1, 0.3, 0.5 wt.%) amount of Ni. The line broadening XRD analysis indicates that the increasing Ni addition decreases the crystallinity of zeolites. The TEM analysis indicates that the average metal particle size increases with increasing Ni addition. The states of Ni and Pt were analyzed by ESCA. The acidity measurements by both TPD of ammonia and pyridine adsorbed FT-IR spectroscopy show the occupation of some of the acid sites by the added Ni species. Ni addition up to 0.3 wt.% over 0.1 wt.% Pt/H-β and 0.1 wt.% over 0.1 wt.% Pt/H-MOR enhances the ethylbenzene conversion, isomerization selectivity and sustainability of the catalysts. Further Ni addition above the threshold value leads to a drastic drop in activity and isomerization selectivity. Zeolite-β-based Ni–Pt catalysts always show higher activity and selectivity than mordenite-based catalysts.

Active Sites in Working Bifunctional GaH-TON Aromatization Catalysts: Kinetic Evaluation

The conversion of light alkanes to high value aromatics proceeds with a high selectivity over bifunctional, gallium (Ga) containing zeolite catalysts. It is generally agreed that Ga sites are involved in dehydrogenation reaction steps and that the zeolite acid sites catalyze cracking, oligomerization, and cyclization reactions. However, understanding of the precise roles of the acid and Ga sites in the reaction mechanisms is significantly hampered since the number of these sites in working catalysts is not known. This paper describes a kinetic approach to evaluation of the acid and Ga active sites in working Ga containing TON zeolite catalysts that relies on the analysis of the rates of formation of the primary products of a n-butane aromatization reaction. Our results show that the rate of ethane formation at low n-butane conversions can be used as a quantitative estimate of acidity in working bifunctional zeolite catalysts and demonstrate, for the first time, a significant decrease in the number of Brønsted acid sites in the Ga containing catalysts under reaction conditions: around 47 and 79% for the catalysts with Ga loading of 1.5 and 2.5 wt %, respectively. We conclude that the reduction in acidity is associated with the formation of catalytically active Ga(+) ions and obtain estimates for the number and steady-state turnover activity of the acid and Ga active sites in n-butane transformation. We anticipate that our work will facilitate understanding of the precise roles of the acid and Ga sites in the mechanisms of alkane aromatization and, as a far-reaching implication, will prompt wider use of detailed kinetic studies for the evaluation of active sites in working catalysts.

A Unified Single-Event Microkinetic Model for Alkane Hydroconversion in Different Aggregation States on Pt/H−USY-Zeolites

A single-event microkinetic model for the catalytic hydroconversion of hydrocarbons on Pt/H-US-Y bifunctional zeolite catalysts developed for low-pressure vapor phase conditions was extended to cover high-pressure vapor phase and liquid phase conditions. The effect of the density of the bulk hydrocarbon phase on the physisorption as well as on the protonation steps of the reaction network was accounted for explicitly and can be interpreted in terms of "compression" of the hydrocarbon sorbate inside the zeolite pores and "solvation" of the catalyst framework by the dense bulk hydrocarbon phase. The bulk phase density effect on the physisorbed state is described via a single excess free enthalpy of physisorption. A dense bulk hydrocarbon phase destabilizes the sorbate molecules inside the catalyst pores. An expression of the excess free enthalpy of physisorption involving the fugacity coefficient and a zeolite dependent factor allows description of physisorption data. Typical excess free enthalpy values are in the range 1.5-5.1 kJ mol(-1) increasing with carbon number in the series of C5-C16 alkanes. At high-pressure vapor phase and liquid phase conditions, the excess standard protonation enthalpy is estimated at -7.8 kJ mol(-1) leading to relatively more stable carbenium ions at dense bulk phase conditions. As a result of the excess physisorption and protonation properties, the lightest hydrocarbons in mixtures are more competitive at dense phase conditions and their conversion is enhanced compared to low-density conditions.

Improving bifunctional zeolite catalysts for alkane hydroisomerization via gas phase sulfation

Pt-containing H-BEA zeolites were functionalized with sulfate anions via H 2S chemisorption followed by oxidation. This treatment generates sulfate groups and Brønsted acidic sites, modifies the supported metal particles, and leads to higher activity and selectivity for pentane hydroisomerization. The strength and the accessibility of the acid sites present in the parent material were not affected by this procedure. The concentration of Brønsted acidic sites and the catalytic activity for light alkane isomerization varied sympathetically. The parallel increase in isomerization selectivity indicates that either the residence time of the alkoxy intermediates decreases for the modified samples (suppressing undesired cracking reactions on the acid sites) or the selective decoration of the Pt particles with sulfur reduces hydrogenolysis on the metal particles.