Longer Catalyst Lifetime Research Articles

Selective and efficient production of 1,5-pentanediol from tetrahydrofurfuryl alcohol using Ni-La(OH)3 catalysts

Biomass-derived furfural and its derivatives are promising feedstocks for producing valuable C5 diols by catalytic hydrolysis. However, this process requires selective ring opening of tetrahydrofurfuryl alcohol (THFA) to 1,5-pentanediol, which is challenging. Here we report efficient route for this conversion using Ni-La(OH)3 catalysts prepared by a green co-precipitation-hydrothermal method. We show that these catalysts can achieve up to 91.7% yield and 94.6% selectivity of 1,5-pentanediol from THFA under mild conditions. We elucidate the key role of the La(OH)3 phase, the basic sites and the Nin+-O-La3+ structure of the catalysts in promoting the selective hydrogenolysis and ring opening of THFA. We also demonstrate that the co-dehydrogenation of secondary alcohols enables lower reaction pressure and longer catalyst lifetime. Our work provides a sustainable and environmentally benign approach for producing 1,5-pentanediol from biomass-based furfural and its derivatives, which has potential applications in polymer synthesis and green chemistry.

Simultaneously enhanced aromatics selectivity and catalyst lifetime in methanol aromatization over [Zn, Al]-ZSM-5 via isomorphous substitution with optimized acidic properties and pore structure

Zinc-modified HZSM-5 zeolites as efficient catalysts have been widely applied in methanol to aromatics (MTA) reactions, however, the relationship between aromatics selectivity and catalytic stability in traditionally loaded catalysts seems to be a stubborn trade-off. To improve both catalytic indicators simultaneously and reveal the relation of the states of introduced Zn species to the consequential influence in physiochemical properties, a series of [Zn, Al]-Z5 zeolites with different Zn contents were prepared via isomorphous substitution under a fixed Si/Me (Me = Al or Al and Zn) ratio. Results revealed that there were three possible states of the introduced Zn species, namely the highly-dispersed ZnO phase, the Zn(OH)+ occupying the ion-exchange sites, and the tetra-coordinated ZnO42- integrated into the zeolite framework. A portion of Zn was successfully integrated into the five-membered rings of zeolite in the form of Si-O(H)-Zn, which played the role of strong Brönsted acid sites and led to the formation of hierarchical structures aside from the intrinsic micropores. Besides, extra-framework Zn(OH)+ was formed by the interaction between dissociate Zn species and the Si-O(H)-Al structure, giving rise to larger proportions of Lewis acid sites. Benefitting from the optimized acidic properties and pore structure, 0.5[Zn, Al]-Z5 exhibited higher aromatics selectivity and longer catalyst lifetime (26.0% and 132 h) than [Al]-Z5 without Zn addition (19.6% and 52 h) in methanol aromatization. Overall, our findings opened a new way to improve the efficiency of MTA reaction and broadened the method to obtain metal-modified zeolite catalysts.

Enhanced catalytic performance of hierarchical Zn/ZSM-5 with balanced acidities synthesized utilizing ZIF-14 as porogen and Zn source in methanol to aromatics

A series of Zn loaded ZSM-5 (Zn/ZSM-5) zeolites were prepared utilizing either Zn(NO3)2 or Zn-based MOFs (ZIF-61, ZIF-8 and ZIF-14) as Zn sources to explore their effects on the catalysts’ physiochemical properties through characterizations and simulations. Results revealed that hierarchical structures containing meso- to macro- pores of 10∼80 nm aside from the intrinsic micropores were constructed profiting from the use of Zn-based MOFs. On the other side, lager proportions of medium acid and Lewis acid sites were generated by more Zn(OH)+, whose content was proven to be inextricably linked to the binding energy between Zn and ligand as well as local charge valence state of Zn. Benefitting from hierarchical structures and balanced acidities, Zn/Z5(ZIF-14) employing ZIF-14 as Zn source demonstrated higher aromatic selectivity and longer catalyst lifetime (50.9% and 26 h) than the microporous counterpart synthesized from zinc nitrate hexahydrate (42.1% and 20 h) in methanol to aromatics (MTA) reaction.

Catalytic upgradation of crude glycerol to produce bio-based aromatics over hierarchical MFI zeolite: Effect of bimodal hierarchical porosity enhancement and porosity-acidity interaction

The transformation of renewable biomass derived crude glycerol into value-added BTX aromatics is an attractive approach to facilitate carbon neutrality and recycling economy. Herein, two kinds of hierarchical HZSM-5 with distinct hierarchical porosity and acidity distribution were synthesized based on a seed-induced method by utilizing CTAB and TPOAC as soft mesoporogens, respectively. And the effects of bimodal hierarchical porosity and porosity-acidity interaction on the upgradation efficiency during the conversion of crude glycerol over hierarchical HZSM-5 were investigated. The abundant intra-mesopores and promoted porosity-acidity interaction in hierarchical HZSM-5 facilitated the transformation of macromolecules in crude glycerol into small oxygenated chemicals and olefins, resulting in higher BTX yield and longer catalyst lifetime. Among all catalysts, the hierarchical HZSM-5 sample templated with TPOAC exhibited the maximum carbon yields of BTX (38.5%) and longest lifetime (23 h) due to the better interconnectivity of shape-selective micropores and high mass transfer intra-mesopores. The reaction route and product distribution of upgradation of crude glycerol was strongly dependent on the morphology, bimodal hierarchical porosity and acidity variation resulting from the generation of intra-mesopores in HZSM-5 catalysts by the usage of different soft mesoporogens. The liquid route and side alkylation reaction was accelerated over HZSM-5/TPOAC catalyst while the gas route and secondary coking reaction was promoted over HZSM-5/CTAB sample.

Methanol Aromatization over Zn and Ce Modified Hierarchical ZSM-5 Catalysts: Effect of Ce as a Promoter

Zinc (Zn) and cerium (Ce) modified hierarchical ZSM-5 (HZ) catalysts were prepared by incipient wetness impregnation, and their catalytic performances in methanol to aromatics reaction were evaluated in a fixed-bed reactor operating at 400°C under 0.1 MPa and WHSV of 1.0 h−1. The structure, acidity, and state of Zn species of the Zn/Ce modified HZ catalysts were investigated via several characterization techniques, including XRD, NH3-TPD, H2-TPR, nitrogen adsorption, and XPS. The results showed that the aromatization activity of 2 wt% Zn-modified HZ (2% Zn/HZ) could be significantly enhanced by loading 0.6 wt% Ce, which was mainly attributed to the increase in surface ZnOH+ species. Moreover, it was found that Ce inhibited pore blockage caused by Zn. Consequently, compared to 2% Zn/HZ, 2% Zn-0.6% Ce/HZ exhibited higher aromatic selectivity and longer catalyst lifetime.

Enhancement of catalytic activity by addition of chlorine in chemical vapor deposition growth of carbon nanotube forests

In carbon nanotube (CNT) growth, the role of catalytic nanoparticles involves complex processes of feedstock gas decomposition, carbon feedstock transport, and CNT crystal precipitation. We report on the improvement of the catalytic activity by chlorine addition during the CNT forest growth process. The addition of Cl2 enhanced the diffusion rate of carbon in the catalysts, and thus changed the rate-limiting step from iron diffusion in the catalyst to the feedstock gas decomposition on the catalyst surface, leading to a higher growth rate and longer catalyst lifetime. The addition of Cl2 directly affected numerous CNT structural parameters, including the CNT diameter, number of walls, and crystal quality. Furthermore, the Cl2 addition made the CNT forest super-aligned, and it enhanced the dry spin capability of the CNT forests, allowing CNT webs to be continuously drawn from the forests.

One-pot synthesis of [Mn,H]ZSM-5 and the role of Mn in methanol-to-propylene reaction

A Mn-modified ZSM-5 zeolite (Mn-HZ) was synthesized using a quasi-solid-phase method, and its physicochemical properties were characterized. The presence of tetracoordinated framework Mn(III) was confirmed using ultraviolet–visible and Raman spectroscopy measurements, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction, and the results suggest that Mn entered the framework structure of ZSM-5. Crucially, the introduction of Mn increased the weak Brønsted acid site content and decreased the strong acid site content and resulted in an increase in the amount of framework Al in the straight zeolite channels. During application for the methanol-to-propylene reaction (MTP), Mn-HZ produced fewer aromatics and had a lower carbon deposition rate than the unmodified zeolite, resulting in a longer catalyst lifetime and higher selectivity for propylene and butene. In addition, a mechanism for the MTP reaction is proposed based on the detection of ethylene in high concentrations in the initial stages of the reaction, suggesting that it could be the initial hydrocarbon pool species. Overall, our results indicate that Mn-HZ favored the olefin-based cyclic mechanism to the aromatic-based mechanism.

The Selective Conversion of Methyl and Ethyl Acetate to High Content Alkyl Aromatic Hydrocarbons over H-ZSM5

This research is devoted to a catalytic process using the H-ZSM5 catalyst for the conversion of methyl and ethyl acetate to hydrocarbon aromatics. These reactions are carried out in a fixed bed reactor under atmospheric pressure at 370°C. The distribution of products was measured by GC-Mass spectrometer. The variation of weight hourly space velocity (WHSV) on the conversion of these esters to aromatic hydrocarbons showed a significant effect on carbon distribution. The deactivation catalyst by time was monitored using product selectivity and conversion. The production of alkyl and poly alkyl aromatic compounds was formed under controlled conditions. The advantages of these methods are the formation of a higher concentration of octane number booster poly alkyl aromatic compounds (mono-aromatics) from esters as starting materials. Moreover, the catalyst lifetime on stream was investigated and exhibited longer catalyst lifetime for ethyl acetate conversion than methyl acetate.

Oxidation kinetics of 2‐methyl‐1,3‐propanediol to methacrylic acid in a fluidized bed reactor

AbstractMethacrylic acid (MAA) is a specialty monomer for poly methyl methacrylate (PMMA). Partial oxidation of 2‐methyl‐1,3‐propanediol (2MDPO) to MAA is an alternative to commercial technology with fewer process steps, less cost and toxic feedstocks, and longer catalyst lifetime. Here, we evaluated the effect of 2MPDO and oxygen concentrations, reaction temperature, and contact time on product selectivity and 2MPDO conversion over VOCu0.5/Cs(NH4)2PMo12O40. Higher temperature increases selectivity and conversion; MAA selectivity reached 46% at 69% 2MPDO conversion. Higher 2MPDO to O2 ratio favours higher MAA selectivity due to methacrolein (intermediate) oxidation to MAA (a higher ratio favours consecutive oxidation) or lower combustion of MAA to COx. Shorter contact times decrease MAA selectivity. The Mars van Krevelen model characterizes the experimental data better than both the Langmuir‐Hinshelwood or Eley‐Rideal models; The reaction sequence involves both direct and indirect reactions in which 2MPDO reacts to methacrolein (MAC) as an intermediate and then it oxidizes to MAA (indirect) and/or 2MPDO directly oxidizes to MAA but the indirect reaction rate to MAA is 50 times faster than the direct reaction rate. The reaction is first order with respect 2MPDO and oxygen, and the rate‐limiting step is 2MPDO activation on oxidized sites.

Catalytic Conversion of Chloromethane to Olefins and Aromatics Over Zeolite Catalysts

We report the tunable conversion of chloromethane to olefins and aromatics using different metal-promoted zeolites as catalysts. Despite SAPO-34 was industrially used as catalysts for methanol to olefins reaction (MTO), the SAPO-34 based zeolites exhibited low activity and short lifetime when using chloromethane as the feed. Higher chloromethane conversion and longer catalyst lifetime were found on H-ZSM-5. The activity and product distribution can be improved by optimizing the reaction temperature and space velocity. Impregnating the H-ZSM-5 zeolite with 1 wt% and 5 wt% metal oxide as promoters significantly enhanced the conversion efficiency and altered the product distribution. The highest aromatics selectivity (38%) was obtained on the H-ZSM-5 zeolite promoted by 5 wt% Ni, whereas on 5 wt% Mg and 5 wt% Mn promoted H-ZSM-5, the aromatics selectivity is merely 5%. Therefore, different modified H-ZSM-5 could be used to convert chloromethane to either aromatics or olefin-heavy products. It was found that the aromatics yield is strongly correlated to the acidity of the H-ZSM-5 zeolite.

A green and cost-effective surfactant-assisted synthesis of SAPO-34 using dual microporous templates with improved performance in MTO reaction

The SAPO-34 catalysts were successfully synthesized with different amounts of a cheap and green nonionic surfactant (Triton X-100) as a mesoporogen additive and MOR/TEAOH as microporous mixed templates. The prepared samples were characterized and tested in the methanol to olefins (MTO) reaction under the industrial feed composition of 72 wt% methanol in water. The results revealed that the surfactant concentration affects the acidity, particle size, and textural properties which results in different catalytic performances. The sample prepared with the surfactant molar ratio of 0.02 exhibits a 12% improvement in the light olefins selectivity (90%) as well as the longer catalyst lifetime (more than 330 min) compared to the parent one (79.3% selectivity and 260 min lifetime). This could be attributed to the high crystallinity, smaller crystallite size, proper lower acidity, higher surface area, and the facilitation of reactants and product transportation through mesoporosity created in the structure of crystals.

One-pot synthesis of VO x /Al 2 O 3 as efficient catalysts for propane dehydrogenation.

Vanadium oxides, as highly efficiently catalysts, are widely applied in various catalytic reactions, such as the dehydrogenation of light alkanes and epoxidation of alkenes. In this paper, a series of VO x /Al 2 O 3 catalysts were fabricated by the 1-pot method for catalytic propane dehydrogenation. The results indicated that the VO x /Al 2 O 3 catalysts with loading of 10 wt.% vanadium exhibited optimized catalytic performance. The as-prepared catalysts were characterized by N 2 adsorption-desorption, XRD, TEM, H 2 -TPR, and XPS to explore the texture properties, morphology, and electronic environment of vanadium. In addition, several vanadium catalysts were also prepared by the incipient wetness impregnation (IWI) method to compare their catalytic performance with the 1-pot synthesized catalysts. The catalysts synthesized by the 1-pot method exhibited higher selectivity of propylene and longer catalyst lifetime at high propane conversion when compared to the counterpart synthesized by the IWI method.

Shape selectivity conversion of biomass derived glycerol to aromatics over hierarchical HZSM-5 zeolites prepared by successive steaming and alkaline leaching: Impact of acid properties and pore constraint

The selective production of light aromatics starting from biomass derived glycerol provides excellent prospect in reducing dependency on fossil resources and carbon dioxide emissions. The catalytic perfomances in glycerol to aromatics (GTA) procedure were systematically investigated for HZSM-5 catalysts with various porosity and acidic property, which were prepared by separate or multi-step treatments using NaOH and steaming on HZSM-5 zeolites. A consecutive steaming-alkali treatment of HZSM-5 zeolite enables the introduction of higher amounts of intra-mesoporosity with smaller-aperture (mainly at the range of 2–4 nm), which could be ascribed to the easier extraction of Si species in steaming treated HZSM-5 interior than that in steaming treated HZSM-5 outer surface. However, the combination of alkali-steaming treatment of HZSM-5 zeolite leads to a remarkable collapsion in the generated micro-mesopore hierarchical structure. Both the GTA reaction and coking process were varied with the HZSM-5 catalyst prepared by different post treatment means. Among all catalysts, 3 h 450 °C/0.3 M NaOH/HZSM-5 catalyst exhibited the highest BTX aroamtics yield, lowest coking rate and longest catalyst lifetime, which could be ascribed to the synergistic effect between the shape selectivity of micropores and size confinement of mesopores coupling with moderate acidity distribution in HZSM-5 crystals interior and surface for GTA process.

Gd-Enhanced Growth of Multi-Millimeter-Tall Forests of Single-Wall Carbon Nanotubes.

Multi-millimeter-tall vertically aligned single-wall carbon nanotube (VA-SWCNT) forests were grown using Fe/Gd/Al2Ox catalyst with high initial growth rate of ∼2 μm s-1 and long catalyst lifetime of ∼70 min at 800 °C. The addition of Gd with a nominal thickness of 0.3 nm drastically prolonged the catalyst lifetime. The analysis of the VA-SWCNT forests by a transmission electron microscope showed that the average diameter of the SWCNTs grown with Gd is constant from the top to the bottom of the forests, while it monotonically increased without Gd. This indicated that Gd suppresses the structure change of the Fe nanoparticles in the lateral direction during the CNT growth. By X-ray photoelectron spectroscopy, it was found that the longer catalyst lifetime with Gd stems from the suppression of the interaction between Fe and C resulting in the smaller structure change of the Fe nanoparticles.

Mesoporogen‐Free Synthesis of High‐Silica Hierarchically Structured ZSM‐5 Zeolites and their Superior Performance for the Methanol‐to‐Propylene Reaction

A series of hierarchically structured ZSM‐5 zeolites (ZSM‐5 HSZs) with a Si/Al ratio of about 200 have been successfully synthesized in the absence of additional mesoporous agents. XRD, N2 sorption isotherms, SEM, TEM and NH3‐TPD results showed that the obtained HSZs materials possess high crystallinity, interconnected micro/mesoporous structures and similar total acid amounts. Meanwhile, in the methanol‐to‐propylene (MTP) reaction, compared to the microporous counterpart, all synthesized ZSM‐5 HSZs demonstrated superior performance benefitting from their hierarchical porous structures. Interestingly, 27Al MAS NMR and Py‐FTIR results confirmed the inter‐transformation of framework and extra‐framework Al species with the extension of materials crystallization duration and consequently the variation of materials surface acidity. As a result, the optimized catalyst achieved the highest initial propylene selectivity of 54.4 % and the longest catalyst lifetime (t90) of 175 h under the weight hourly space velocity (WHSV) of 1.0 g g–1 h–1. Moreover, a new “in situ alkali etching‐hydrothermal restoring“ mechanism has been proposed to elucidate the structural evolution of here reported high‐silica ZSM‐5 HSZs during the synthesis.

Alkylation of isobutane/butene promoted by fluoride-containing ionic liquids

In this work, the alkylation of isobutane and butene, catalyzed by sulfuric acid in the presence of the fluoride–containing ionic liquids [Bmim][PF6] and [Bmim][SbF6], was investigated. The use of the binary mixture catalysts brought to a higher C8 selectivity and longer catalyst lifetime, compared with the results obtained when working with sulfuric acid only. This was attributed to the formation of new species when [Bmim][PF6] or [Bmim][SbF6] are added to sulfuric acid. The acidolysis of [Bmim][PF6] and [Bmim][SbF6] was accompanied by the release of hydrogen fluoride (HF) and the decomposition of anions to [PF6−x−2y(HSO4)x(SO4)y]− and [SbF6−x−2y(HSO4)x(SO4)y]−, respectively. The presence of these new species after acidolysis was measured and confirmed by ion chromatography, 1H–Nuclear Magnetic Resonance (NMR), 19F–NMR and 31P–NMR. The production of HF and the complexation of anions and carbenium ions both play an important role in stabilizing the carbenium ion and improving the catalytic performance.

Enhanced MTO performance over acid treated hierarchical SAPO-34

Hierarchical SAPO-34 crystals were synthesized by a facile acid etching post-treatment. Butterfly-shaped porous patterns on four side faces and hierarchical pores composed of micropores, mesopores and macropores were formed after a nitric acid or oxalic acid treatment. The catalytic performance of the hierarchical SAPO-34 for the methanol to olefins (MTO) process showed that the synergistic effect of the hierarchical pores and acid sites resulted in a longer catalyst lifetime (from 210 to 390 min for the acid treated SAPO-34) and higher selectivity to light olefins of 92%–94%. The ethylene selectivity can be adjusted between 37.4% and 51.5% by the pore size. No hierarchical SAPO-34 was obtained after a treatment with butanedioic acid, and with this sample, fast deactivation was detected after 100 min.

The multiple benefits of glycerol conversion to acrolein and acrylic acid catalyzed by vanadium oxides supported on micro-mesoporous MFI zeolites

The ZSM-5 zeolite (MFI structure, Si/Al=40) was treated using NaOH and either oxalic acid or HCl to obtain hierarchical materials with different characteristics, followed by impregnation with vanadium oxides (V2O5) to generate redox-active sites. The impact of the multiple treatments on the efficiency and stability of the catalysts in the conversion of glycerol to acrolein and acrylic acid was investigated and correlated with catalyst porosity, acidity, and chemical composition. The treated and impregnated V2O5 catalysts were subjected to XRD, 27Al NMR, nitrogen physisorption, TPD-NH3, TG, and UV–Vis analyses, in order to associate the properties of the catalysts with their activities. The studies showed that the catalytic performance of the materials depended on the acidic and textural properties of the zeolites, which influenced both the dispersion of V2O5 and its interaction with the acid sites of the supporting zeolites. All the catalysts provided conversion values exceeding 65%, even after 6h on glycerol stream. The distribution of products strongly reflected the effects of pore formation, acid treatment with oxalic acid or HCl, and the presence of vanadium oxide. The effects of these modifications resulted in higher selectivity to acrolein and acrylic acid, a reduced rate of coke accumulation in the zeolite, and a longer catalyst lifetime.

Steam-dealuminated, OSDA-free RHO and KFI-type zeolites as catalysts for the methanol-to-olefins reaction

RHO and KFI-type zeolites are synthesized in the absence of organic structure-directing agents (OSDAs), post-synthetically dealuminated via high temperature (600–800 °C) steam treatments, and evaluated as catalysts for converting methanol-to-light olefins (MTO). The proton forms of the as-made zeolites deactivate rapidly when tested for the MTO reaction (conducted at 400 °C and atmospheric pressure) due to their high aluminum content. Steam treatments lead to improvements in olefin selectivities and catalyst lifetimes with samples steamed at 600 °C giving the best combination of lifetime and olefin selectivity. Zeolite characterizations by 27Al NMR, 29Si NMR and argon physisorption indicate that the steam treatments extract framework aluminum, leading to reductions in the total number of Brønsted acid sites and the creation of mesopores that can facilitate transport of reactants. Poisoning of the acid sites external to the 8MR pores of the zeolites by treatments with trimethylphosphite results in longer catalyst lifetimes but do not affect the observed olefin selectivities, suggesting that olefins do not undergo secondary dimerization or methylation reactions at these sites.

Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation.

Recent developments in polyester synthesis have established several systems based on zinc, chromium, cobalt, and aluminum catalysts for the ring-opening alternating copolymerization of epoxides with cyclic anhydrides. However, to date, regioselective processes for this copolymerization have remained relatively unexplored. Herein we report the development of a highly active, regioselective system for the copolymerization of a variety of terminal epoxides and cyclic anhydrides. Unexpectedly, electron withdrawing substituents on the salen framework resulted in a more redox stable Co(III) species and longer catalyst lifetime. Using enantiopure propylene oxide, we synthesized semicrystalline polyesters via the copolymerization of a range of epoxide/anhydride monomer pairs.