Metal Acid Balance Research Articles

Unraveling the role of water in mechanism changes for economically viable catalytic plastic upcycling

The surge in global plastic production, reaching 400.3 million tons in 2022, has exacerbated environmental pollution, with only 11% of plastic being recycled. Catalytic recycling, particularly through hydrogenolysis and hydrocracking, offers a promising avenue for upcycling polyolefin plastic, comprising 55% of global plastic waste. This study investigates the influence of water on polyolefin depolymerization using Ru catalysts, revealing a promotional effect only when both metal and acid sites, particularly Brønsted acid site, are present. Findings highlight the impact of Ru content, metal-acid balance, and their proximity on this interaction, as well as their role in modulating the isomerization process, affecting product selectivity. Additionally, the interaction facilitates the suppression of coke formation, ultimately enhancing catalyst stability. A comprehensive techno-economic and life cycle assessment underscores the viability and environmental benefits of the process, particularly in the presence of water. These insights advance understanding and offer strategies for optimizing polyolefin plastic recycling processes.

Solid-state synthesis of aluminophosphate-based zeotypes from conventional amorphous precursors: Strategy and catalytic performance

Exploring novel strategies for the preparation of zeolitic materials with high performance continues to be of great significance. Here we report a general solid-state approach for fabricating aluminophosphate (AlPO)-based zeotypes by directly calcining conventional amorphous precursors at 300 °C for just 30 min. Accordingly, AEL, AFI, LTA and CHA types of AlPO-based zeotypes with high crystallinity and similar textural properties to those of counterparts made by established synthesis approaches have been synthesized. As a demonstration, the catalytic performance of Mg-substituted AlPO-11 (S-MgAlPO-11) in hydroisomerization of n-hexadecane (n-C16) was also investigated. Compared with the Pt supported on conventional MgAlPO-11 (Pt/C-MgAlPO-11) catalyst, the Pt/S-MgAlPO-11catalyst exhibits higher isomerized (87 % vs. 84 %), multi-branched C16 (48 % vs. 30 %) yields and superior reaction stability, attributing to the improved diffusion property and appropriate metal-acid balance. This strategy provides an efficient approach to synthesis promising zeolitic catalysts for industrial applications.

Hydroconversion of waste polyethylene plastics under mild conditions using mechanically mixed bifunctional catalysts: Impact of metal-acid balance and proximity

The disposal of non-biodegradable waste polyolefin plastics poses a serious environmental threat, highlighting the need for cleaner and more efficient thermochemical recycling technologies. This study introduces a scalable mechanical method to synthesize a metal-acid bifunctional catalyst. The mechanical ball milling process not only exposes more acidic sites but also enhances metal-acid proximity without blocking the pores. By varying the metal-acid balance (MAB) through different mixing ratios, we achieved higher yields and selectivity for soluble products at the optimal MAB level. Under mild conditions (250°C) for 8 h, polyethylene (PE) is efficiently converted into liquid phase iso-paraffins with an isomer selectivity of up to 56 % in the diesel and aviation kerosene fractions (C11-C18). This research underscores the importance of the accessibility of acidic sites to long-chain macromolecules, metal-acid site distance, and their balance in the hydrocracking of PE. It provides valuable theoretical insights and catalytic strategies for converting waste PE plastics into high-value fuel fractions.

Catalytic Hydrodeoxygenation of Mixed Plastic Wastes into Sustainable Naphthenes.

The chemical upcycling of plastic wastes by converting them into valuable fuels and chemicals represents a sustainable approach as opposed to landfilling and incineration. However, it encounters challenges in dealing with mixed plastic wastes due to their complex composition and sorting/cleaning costs. Here, we present a one-pot hydrodeoxygenation (HDO) method for converting mixed plastic wastes containing poly(ethylene terephthalate) (PET), polycarbonate (PC), and poly(phenylene oxide) (PPO) into sustainable naphthenes under mild reaction conditions. To facilitate this process, we developed a cost-effective, contaminant-tolerant, and reusable Ni/HZSM-5 bifunctional catalyst through an ethylene glycol-assisted impregnation method. The metallic Ni site plays a pivotal role in catalyzing C-O and C-C cleavages as well as hydrogenation reactions, while the acidic site of HZSM-5 facilitates dehydration and isomerization reactions. The collaboration between metal and acid dual sites on Ni/HZSM-5 enabled efficient HDO of a wide range of substrates, including bottles, textile fibers, pellets, sheets, CDs/DVDs, and plastics without cleaning or pigments removal and even their various mixtures, into naphthenes with a high yield up to 99% at 250 °C and 4 MPa H2 within 4-6 h. Furthermore, the metal-acid balance of the Ni/HZSM-5 catalyst is crucial for determining both HDO activity and product distribution. This proposed one-pot HDO process utilizing earth-abundant metal catalysts provides a promising avenue toward practical valorization of mixed plastic wastes.

In situ synthesis of nanosized ZSM-12 zeolite isomorphously substituted by gallium for the n-hexadecane hydroisomerization

The ZSM-12 zeolite has attracted attention as the promising acid component of bifunctional catalysts for the n -alkane hydroisomerization because of its large size of micropore openings (0.57 nm × 0.61 nm) with 12-membered-ring and one-dimensional channels. However, the larger crystal size and stronger Brønsted acid strength of microsized ZSM-12 zeolite will lead to cracking of iso -olefin intermediates and decrease the iso -alkane yield. In this study, ZSM-12 zeolite samples partially and completely isomorphously substituted with gallium ([Ga,Al]Z12 and GaZ12) were in situ synthesized. The characteristic results indicate that isomorphous substitution by Ga can effectively reduce the crystal size to increase the mesoporosity and weaken the Brønsted acidity of the [Ga,Al]Z12 and GaZ12 samples. In addition, bifunctional catalysts with more appropriate metal-acid proximity for n -hexadecane hydroisomerization were prepared by mixing the 0.6Pd/A sample with 0.6 wt.% Pd loaded on γ-Al2O3 and the ZSM-12, [Ga,Al]Z12 and GaZ12 samples, respectively. The 0.3Pd/A-[Ga,Al]Z12 and 0.3Pd/A-GaZ12 catalysts both promote the maximum iso -hexadecane yield and distribution of multi-branched iso -hexadecane products due to their enhanced mesoporosity, reduced Brønsted acid strength, increased CPd/CH+ ratios and improved metal-acid balance. Especially for the 0.3Pd/A-GaZ12 catalyst, when the n -hexadecane conversion is 93.5%, the maximum iso -hexadecane yield reaches 80.6%, and the proportion of multi-branched iso -hexadecane products is 64.6%, which are both the highest among all investigated catalysts. Accordingly, Ga isomorphous substitution is an effective strategy to develop the efficient bifunctional catalysts for hydroisomerization.

Synergistic Catalytic Performance of Pt-Au Bimetallic Catalysts on High-Crystallinity ZSM-23 Zeolite for Hexadecane Hydroisomerization: Metal-Acid Balance and Enhanced Isomerization Selectivity.

Highly crystalline ZSM-23 zeolite, exhibiting a distinctive dumbbell morphology, was synthesized via a hydrothermal method. Bifunctional catalysts, comprising single metals (Pt or Au) and bimetals (Pt-Au), were successfully prepared by using a positional precipitation method. The hydroisomerization of hexadecane served as a model reaction to assess the catalytic performance arising from the synergistic effects of bimetallic active sites. In comparison to single-metal catalysts, 0.3Au0.7Pt/ZSM-23 demonstrated increased n-C16 conversion, while 0.5Au0.5Pt/ZSM-23 exhibited enhanced i-C16 selectivity, achieving the highest i-C16 yield. The bimetallic catalyst not only finely tuned the metal site activity through bimetallic synergy but also achieved a superior balance between metal and acid catalysis, resulting in improved catalytic performance in the n-C16 hydroisomerization. The Pt-Au bimetallic catalyst approached the ideal requirements for a hydroisomerization catalyst, achieving a harmonious balance of metal and acid catalysis.

Selective hydrocracking of 1-methylnaphthalene to benzene/toluene/xylenes (BTX) over NiW/Beta bifunctional catalyst: Effects of metal–acid balance

The hydrocracking catalyst is characteristic of bifunctional catalyst mainly requiring metal–acid balance, which includes metal–acid ratio and metal–acid proximity. Here, we screened and clarified the optimal metal–acid balance on 1-methylnaphthalene (1-MN) hydrocracking by adjusting metal–acid ratio (nM/nA) via physically mixing the γ-Al2O3 supported NiW samples and Beta zeolite with different acidity (denoted as NiW/AB(x) and x presents the molar ratio of SiO2/Al2O3 for Beta zeolite). NiW/AB(60) catalyst with a nM/nA of 0.40 showed the highest BTX selectivity (14.4 %) at a 1-MN conversion of 76.6 %, suggesting an optimal site balance between the metal sulfide site and medium-strong acid sites (ca. 1:2.5). Also, four different metal–acid proximities with centimeter, millimeter, micrometer and nanoscale distances were compared. The nanoscale proximity enabled the highest BTX selectivity (19.6 %) as compared to the microscale (14.4 %), millimeter scale (12.4 %) and centimeter scale (7.1 %) catalysts, confirming that the selectivity of BTX benefited from the fast diffusion for transporting reaction intermediates between metal and acid sites. Thus, we realized a nM/nA of 0.40 and a nanoscale site proximity for improving the reactivity and selectivity of 1-MN hydrocracking. This work not only presents an elegant showcase of achieving the synergistic effects of bifunctional catalyst, but also provides a rational approach for enhancing the catalytic performance of hydrocracking and beyond.

Polyethylene Upgrading to Liquid Fuels Boosted by Atomic Ce Promoters.

Hydrocracking catalysis is a key route to plastic waste upgrading, but the acid site-driven C-C cleavage step is relatively sluggish in conventional bifunctional catalysts, dramatically effecting the overall efficiency. We demonstrate here a facile and efficient way to boost the reactivity of acid sites by introducing Ce promoters into Pt/HY catalysts, thus achieving a better metal-acid balance. Remarkably, 100 % of low-density polyethylene (LDPE) can be converted with 80.9 % selectivity of liquid fuels over the obtained Pt/5Ce-HY catalysts at 300 °C in 2 h. For comparison, Pt/HY only gives 38.8 % of LDPE conversion with 21.3 % selectivity of liquid fuels. Through multiple experimental studies on the structure-performance relationship, the Ce species occupied in the supercage are identified as the actual active sites, which possess remarkably-improved adsorption capability towards short-chain intermediates.

Ni/HZSM-5 catalysts for hydrodeoxygenation of polycarbonate plastic wastes into cycloalkanes for sustainable aviation fuels

Hydrodeoxygenation (HDO) is one of the effective methods for upcycling polycarbonate (PC) plastic waste, but the development of low-cost, high-performance HDO catalysts still faces great challenges. In this work, we report that a bifunctional Ni/HZSM-5 catalyst can directly upgrade PC plastic wastes into sustainable aviation fuel ranged cycloalkanes in high yields (99.3 %) with 81.2 % yield of C15 dicycloalkane under mild reaction conditions (190 °C, 4 MPa H2). Controlled reactions of PC and probe molecules demonstrated the conversion of PC into C15 dicycloalkanes involves PC depolymerization by direct cleavage of C-O bonds adjacent to benzene ring and ester group, forming C15 aromatics and C15 monophenols at the metal sites, followed by hydrogenation of C15 aromatics rings on metallic Ni sites and HDO of C15 monophenols on metal-acid dual sites parallel to generate C15 dicycloalkane. The C-C cracking mainly occurred on the tertiary carbon adjacent to the benzene ring on acidic sites of HZSM-5, thus forming C6∼C9 monocyclic alkanes. The realization of this process can be attributed to the cooperation between metal sites and acid centers on Ni/HZSM-5. Besides, the metal-acid balance (MAB) in Ni/HZSM-5 significantly affected the HDO activity and product distribution. 20Ni/HZSM-5(200) with suitable MAB showed good HDO activity and excellent selectivity to C15 dicycloalkane. In addition, the obtained catalyst was also capable of converting common real PC plastics wastes (CD disk, DVD disk and PC sheet) into cycloalkanes with the yield up to 98 % and exhibited excellent stability. This approach to construct inexpensive bifunctional catalysts highlights an efficient and reliable route for HDO of PC to sustainable aviation fuel, providing a new avenue towards a circular economy.

The effects of growth modifiers on the catalytic performance of hierarchical Pd/ZSM-23 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes catalyzed by metal-zeolite bifunctional catalysts is an important process to produce clean biofuels. The employment of appropriate growth modifiers during the synthesis of hierarchical zeolites to increase the iso-alkane yield has captured much attention. In this work, cetyltrimethylammonium bromide (CTAB) and polydiallyl dimethyl ammonium chloride (PDDA), representatives of cationic surfactants and cationic polyelectrolytes, are added to the initial gel to one-pot synthesize hierarchical ZSM-23 zeolites (Z23-xPC and Z23-yPP) via the bottom-up strategy. The corresponding Pd/ZSM-23 catalysts are prepared by loading 0.5 wt% Pd on microporous and hierarchical ZSM-23 and tested for the hydroisomerization of n-hexadecane. Due to the cationic adsorption of CTAB or steric hindrance effect of PDDA, Z23-xPC and Z23-yPP samples all demonstrate enhanced mesoporosity compared with the conventional microporous Z23-P sample. The diffusivity experiments indicates that the D/L2 values decrease in the order of Pd/Z23-5PP > Pd/Z23-3PC > Pd/Z23-P, suggesting that the hydrocarbons diffusion in the channel of hierarchical ZSM-23 samples is evidently improved. In addition, the Brønsted acid densities of the Z23-xPC and Z23-yPP samples are also evidently reduced compared to that of the microporous Z23-P sample because of the proportion decreases of framework Al atoms at T2-T5 sites. Compared with the microporous Pd/Z23-P catalyst, the appropriate addition amount of growth modifiers can evidently improve the yield of iso-hexadecane products and limit the cracking process. Especially for the Pd/Z23-5PP catalyst, the cracking process is effectively limited and the maximum iso-hexadecane yield of 75.4% is obtained at an n-hexadecane conversion of 88.8% at 290 °C, which is the highest among all catalysts. Therefore, this work has provided an effective method for the simple preparation of bifunctional catalysts with improved diffusion performance and more favorable metal–acid balance.

Design and preparation of Pt@SSZ-13@β core-shell catalyst for hydrocracking of naphthalene

A Pt@SSZ-13@β core-shell catalyst is designed and successfully prepared for investigating the effects of spillover hydrogenation on hydrocracking of naphthalene. The Pt NPs encapsulated in SSZ-13 cages are inaccessible to naphthalene due to its lager size than the pore size of SSZ-13. Thus, hydrogenation functional over Pt@SSZ-13@β is mainly realized via spillover hydrogenation. Pt@SSZ-13@β exhibits higher selectivity to the desired BTX and less naphthenic products than (Pt/SSZ-13)@β and Pt/(SSZ-13@β) at above 90 % naphthalene conversion. These results indicate the hydrogenation modes resulting from the location of the supported Pt NPs in core-structure catalysts can affect the metal-acid balance, and the spillover hydrogenation can effectively suppress the deep hydrogenation of tetralin in hydrocracking of naphthalene, thereby changing the reaction path and improving the selectivity of BTX. In addition, Pt@SSZ-13@β shows a better sulfur-tolerant ability than Pt/(SSZ-13@β). This work provides a new synthetic strategy for preparing zeolite-based bifunctional catalyst.

Hydrocracking of naphthalene over Beta zeolite coupled with NiMo/γ-Al2O3: Investigation of metal and acid balance based on the composition of industrial hydrocracking catalyst

In this work, NiMo/γ-Al2O3 catalysts with the different hydrogenation function were prepared by adjusting the metal composition, while Beta zeolites with the different acidity were synthesized by regulating their Si/Al ratios. The influences of the metal–acid balance on hydrocracking of naphthalene are investigated via coupling the various NiMo/γ-Al2O3 with Beta zeolite (NiMo/γ-Al2O3 + Beta). Compared to NiMo/Beta, NiMo/γ-Al2O3 + Beta displayed the closer catalytic performance in hydrocracking of naphthalene to the catalyst prepared by the method employed in industry, indicating that it is feasible to simulate industrial catalyst through coupling method. The catalytic performance of the coupled catalysts greatly depends on the hydrogenation ability of NiMo/γ-Al2O3 and the acidity of Beta zeolite. The Si/Al ratio, crystal size and amount of the Beta zeolite greatly affect the hydrocracking performance of the coupled catalyst. Ni(2)Mo(13.2)/γ-Al2O3 + Beta(20) exhibited the highest BTX selectivity (62.8%) at 98% naphthalene conversion due to its well-matched hydrogenation and acid function.

The hydroisomerization of n-hexadecane over Pd/SAPOs bifunctional catalysts with different opening size: Features of the diffusion properties in pore channels and the metal-acid synergistic catalysis

In this work, SAPO-11, SAPO-31 and SAPO-41 with one-dimensional channels are synthesized hydrothermally by employing a di-n-butylamine (DBA) template, industrial silicon and aluminum sources, and the corresponding Pd/SAPOs bifunctional catalysts are prepared by loading 0.5 wt% Pd via the wet impregnation method. The diffusivity of n-hexadecane and 2-methylpentadecane in the micropores of different SAPOs is determined by molecular dynamics (MD) simulation, which indicates that the opening size has strong effects on the diffusion property of reactants and intermediates in the micropore channels. The calculated self-diffusion coefficients (Ds) of both n-hexadecane and 2-methylpentadecane based on MD simulation of three SAPOs decrease as SAPO-31 > SAPO-41 > SAPO-11, which is consistent with their minor axis size of micropores. The results of n-hexadecane hydroisomerization test indicate that the Pd/SAPO-31 catalyst shows the highest activity and iso‐hexadecane yield of 85.0% due to the significantly improved diffusion and favorable metal-acid balance. Different from Pd/SAPO-11 and Pd/SAPO-41, hydroisomerization over Pd/SAPO-31 occurs via the key lock mechanism, which leads to an increased multi-branched iso‐hexadecane proportion of 66.3% at the n-hexadecane conversion of 95.3%. The Pd/SAPO-31 catalyst is proven to be a highly effective bifunctional catalyst for the industrial production of bio-diesel with excellent low-temperature fluidity.

Manipulation of hydroisomerization performance on Pt/ZSM-23 by introducing Al2O3

ZSM-23 zeolite was successfully synthesized in a dual-template system, and ZSM-23-Al2O3 composites with different ratios were also prepared. The hydroisomerization performance of Pt/ZSM-23 catalyst was manipulated by introducing Al2O3, and the influence of Al2O3 on physicochemical properties was investigated by XRD, SEM, TEM, N2 physical adsorption-desorption and NH3-TPD characterizations. The results showed that Al2O3 improved the dispersion of Pt, significantly reduced the acid sites concentration of the catalyst, and regulated the metal-acid balance in quantitative. The suitable metal-acid balance concentration could improve the selectivity of isomers and suppress the cracking reactions. Meanwhile, Al2O3 dispersed the ZSM-23 grains, which improved the dispersion and increased the number of exposed pores in ZSM-23. Thus the diffusion efficiency of reactants and intermediates could be promoted and the isomer products selectivity could be improved. All composite catalysts showed high selectivity of isomer products, among which, Pt/(9Z-1Al) had the highest yield of isomer products due to its suitable metal-acid concentration balance, reached 60% at 340 °C, which was a significant improvement compared with Pt/ZSM-23 (42%). When the reaction temperature was lower than 310 °C, the pore mouth mechanism dominated in Pt/ZSM-23, while the key-lock mechanism was significantly strengthened at higher reaction temperature. After the introduction of Al2O3, more adjacent pores in ZSM-23 were exposed and the key-lock mechanism became the domination, which led to a large number of 7/8Me-C15 isomers.

Excellent catalytic performance over hierarchical ZSM-48 zeolite: Cooperative effects of enhanced mesoporosity and highly-accessible acidity

Hydroisomerization has been considered as an effective and efficient route for production of transportation fuels and lubricants with superior cold-flow properties. In current work, n-hexadecane (n-C16) hydroisomerization was investigated over Pt catalysts supported on hierarchical ZSM-48, which was post-treated by multi-step procedures including alkaline-acid, acid-alkaline-acid, steaming-alkaline-acid, and fluorination-alkaline-acid leaching. This work was purposed to construct the secondary mesoporous network, enhance the accessible acid sites in hierarchical ZSM-48 zeolite, and investigate their cooperative effects on hydroisomerization performance. The results demonstrated that the microporosity and the crystallinity were preserved after the controllable leaching, coupled with more exposed accessible acidity and enhanced mesoporosity. High dispersion of Pt particles and quantitative metal-acid balance were unable to be the threats for the sequential acid-catalyzed reaction. The cooperative effects of enhanced mesoporosity and highly-accessible acidity accelerated the diffusion and promoted the proximity of metal sites and acid sites, thereby persuading the treated ZSM-48 samples to exhibit excellent activity and iso-selectivity. The i-C16 yield over Pt/ZSM-48(H) catalyst could reach around 86 wt% at conversion rates of 90 wt% with iso-selectivity of 96 wt%. However, the excessively accessible acid sites in Pt/ZSM-48(F) could induce further skeletal transformation and deteriorate the iso-selectivity, although the mesoporous structure was as well established.

Mixture effects in alkane/cycloalkane hydroconversion over Pt/HUSY: Carbon number impact

Cycloalkanes are known to impact the metal–acid balance of the hydrocracking of n-alkanes with similar carbon number, however, how this impact varies with the carbon number of the components involved is still to be understood in more detail. For this purpose, the hydroconversion of n-octane and tert-butylcyclohexane, and n-decane and methylcyclohexane mixtures was investigated in this work over Pt/HUSY catalyst in both the ideal and the nonideal hydrocracking regime. Irrespective of the hydrocracking regime for pure n-octane, its conversion and isomer yields were significantly lowered upon admixture of tert-butylcyclohexane. On the other hand, n-octane admixture did not impact the tert-butylcyclohexane conversion nor its cyclic isomer yields. Upon methylcyclohexane admixture with n-decane, no impact was observed over the catalyst ensuring ideal hydrocracking of pure n-decane. Over the catalyst with significantly lower Pt loading, which does not ensure ideal hydrocracking of n-decane, methylcyclohexane lowered the n-decane conversion. A slightly negative impact of n-decane admixture on methylcyclohexane conversion was also observed. The observed effects are mainly attributed to the differences in adsorption strengths within the zeolite pores on top of differences in alkane and cycloalkane adsorption on the metal sites.

Hydroisomerization of n-hexadecane over Pt/ZSM-48 catalysts: Effects of metal-acid balance and crystal morphology

The wirelike, rodlike and corolla-like ZSM-48 zeolites with various SiO2/Al2O3 ratios (SARs) were successfully synthesized and exploited for the hydroisomerization of n-hexadecane (n-C16). The influences of metal-acid balance, acid sites quantity, crystal morphology and textural properties on n-C16 hydroisomerization performance were investigated primarily, via various characterization technique such as XRD, FT-IR, SEM, TEM, N2 physisorption, NH3-TPD, and Py-IR. The CPt/CA ratios of various catalysts were calculated for the quantified expression of the metal-acid balance, and the acid sites quantity was seriously crucial for the consecutive acid-catalyzed reaction after CPt/CA ratios satisfied within an ideal range. Large external surface could accelerate the conversion rate, shorten the diffusional constraints and inhibit the cracking. The superiorities of satisfied CPt/CA values (0.12–0.15), high concentration of acid sites (>230 μmol/g) and large external surface (>120 m2/g) persuaded the Pt/Z(P)80, Pt/Z(H)60 and Pt/Z(H)80 samples to demonstrate wonderful hydroisomerization performance with outstanding yield around 80 wt% and excellent i-C16 selectivity over 91 wt%. Although Pt/Z(W)80 and Pt/Z(R)80 samples owned the relatively small crystal, the gloomy catalytic activity of them was observed due to their relatively low concentration of acid sites and external surface. Moreover, the presence of “key-lock” mechanism was verified by the observations of 7-methyl-pentadecane (7MC15) dominating in isomer products.

Interplay of Metal-Acid Balance and Methylcyclohexane Admixture Effect on n-Octane Hydroconversion over Pt/HUSY

Hydroconversion feeds are mixtures comprising alkanes and cycloalkanes, for which the binary impact on the respective reaction pathways, is still not completely understood. Methylcyclohexane admixture on n-octane hydroconversion over Pt/HUSY catalysts has been investigated using the pure compounds and their equimolar mixtures in a wide range of operating conditions. The hydroconversion behavior on catalysts with various Pt loading was examined to investigate the role of the active sites. No impact of methylcyclohexane admixture to n-octane was observed over catalysts which ensured ideal hydrocracking (0.5 and 0.1 wt%Pt). In contrast, methylcyclohexane addition decreased the octane isomer yield at iso-conversion over 0.07 wt%Pt/HYUSY. A lower metal loading of 0.04 wt%Pt led to a pronounced decrease in n-octane conversion in the mixture. The methylcyclohexane conversion was not affected by n-octane addition regardless of the metal-acid balance. The negative admixture impact on the n-octane conversion and isomers yield, combined with the absence of any impact on the methylcyclohexane behavior, was attributed to preferred cycloalkane adsorption on metal sites, resulting in a reduced metal site availability for alkanes. A cycloalkane admixture to an alkane in hydrocracking can, hence, induce a regime shift from ideal to nonideal hydrocracking. Consequently, bifunctional catalysts developed purely for alkane hydroconversion may prove not to be optimal for realistic feeds, including cycloalkanes.

Influences of the metal-acid proximity of Pd-SAPO-31 bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization of n-alkanes over bifunctional catalysts is an effective approach for clean fuel production. However, it is still challenging to achieve metal-acid synergy and enhance the catalytic performance by preparation of bifunctional catalysts with suitable proximity between the metal sites and Brønsted acid sites. In this work, three series of bifunctional catalysts with different metal-acid proximities are prepared simply by mixing of SAPO-31 supported Pd (xPd/S) and γ-Al2O3 powders (xPd/S-A(C)), γ-Al2O3 supported Pd samples (xPd/A) and SAPO-31 powders (xPd/A-S(M)), and the mechanical mixing of shaped xPd/A and SAPO-31 granules (xPd/A-S(F)), respectively. The physico-chemical properties and the catalytic performance for the hydroisomerization of n-hexadecane have been investigated. Compared with the xPd/S-A(C) catalysts with the closest proximity between two active sites, the xPd/A-S(M) catalysts with moderate proximity at the micrometer scale demonstrate enhanced catalytic performance in the n-hexadecane hydroisomerization at temperatures above 340 °C. Inparticular, for the 0.15Pd/A-S(M) catalyst with a loading of 0.15 wt% Pd, the highest iso‐hexadecane yield of 80.4% was obtained at the n-hexadecane conversion of 90.4%. Therefore, this work provides an effective route for the simple preparation of bifunctional catalysts with lower Pd loading and favorable metal-acid balance for highly selective hydroisomerization of long-chain n-alkanes.

Shape Selectivity in Hydroisomerization of n-Hexadecane over Pd Supported on Zeolites: ZSM-22, ZSM-12 and Beta

The development of bifunctional catalysts with high branched isomers selectivity in hydroisomerization of n-alkanes constantly remains crucial for the manufacture of green biodiesel from vegetable oil. Herein, three bifunctional catalysts (Pd/zeolite) have been prepared by providing 0.5 wt % Pd over the ZSM-12, ZSM-22 and Beta zeolite, respectively. The physicochemical properties of above-prepared zeolites and catalysts were investigated by XRD, SEM, N2 physical adsorption, NH3-TPD, Py-IR measurements and H2 chemisorption methods. The catalytic property for the n-hexadecane hydroisomerization over three bifunctional catalysts was measured which indicate that higher distribution of mono-branched iso-hexadecane is received over Pd/ZSM-22 and Pd/ZSM-12 catalysts based on the zeolites with one dimensional pore channel due to the high shape selectivity. Compared with Pd/ZSM-12, the Pd/ZSM-22 catalyst displays the higher selectivity for iso-hexadecane because of more favorable metal-acid balance caused by the larger CPd/CH+ ratio. Furthermore, the Pd/Beta catalyst shows highest catalytic activity and maximum iso-hexadecane yield of 69.7% when the n-hexadecane conversion is 78.9%, which results from the maximal porosity, Bronsted acid sites density and mild acidity.