1,519 research outputs found
Supported molybdenum oxides as effective catalysts for the catalytic fast pyrolysis of lignocellulosic biomass
No full textThe catalytic fast pyrolysis (CFP) of pine was investigated over 10 wt% MoO[subscript 3]/TiO[subscript 2] and MoO[subscript 3]/ZrO[subscript 2] at 500 °C and H[subscript 2] pressures ≤0.75 bar. The product distributions were monitored in real time using a molecular beam mass spectrometer (MBMS). Both supported MoO[subscript 3] catalysts show different levels of deoxygenation based on the cumulative biomass to MoO[subscript 3] mass ratio exposed to the catalytic bed. For biomass to MoO[subscript 3] mass ratios <1.5, predominantly olefinic and aromatic hydrocarbons are produced with no detectable oxygen-containing species. For ratios ≥1.5, partially deoxygenated species comprised of furans and phenols are observed, with a concomitant decrease of olefinic and aromatic hydrocarbons. For ratios ≥5, primary pyrolysis vapours break through the bed, indicating the onset of catalyst deactivation. Product quantification with a tandem micropyrolyzer–GCMS setup shows that fresh supported MoO[subscript 3] catalysts convert ca. 27 mol% of the original carbon into hydrocarbons comprised predominantly of aromatics (7 C%), olefins (18 C%) and paraffins (2 C%), comparable to the total hydrocarbon yield obtained with HZSM-5 operated under similar reaction conditions. Post-reaction XPS analysis on supported MoO[subscript 3]/ZrO[subscript 2] and MoO[subscript 3]/TiO[subscript 2] catalysts reveal that ca. 50% of Mo surface species exist in their partially reduced forms (i.e., Mo5[superscript +] and Mo3[superscript +]), and that catalyst deactivation is likely associated to coking.BP (Firm) (MIT Energy Initiative. Advanced Conversion Research Program)National Science Foundation (U.S.) (Award 1454299
Self-assembly of noble metal monolayers on transition metal carbide nanoparticle catalysts
No full textWe demonstrated the self-assembly of transition metal carbide nanoparticles coated with atomically thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti[subscript 0.1]W[subscript 0.9]C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts.United States. Dept. of Energy. Office of Basic Energy Sciences (Grant DE-FG02-12ER16352)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374)Swiss National Science Foundation (Project P2EZP2_159124
Synthesis of Itaconic Acid Ester Analogues via Self-Aldol Condensation of Ethyl Pyruvate Catalyzed by Hafnium BEA Zeolites
No full textLewis acidic zeolites are used to synthesize unsaturated dicarboxylic acid esters via aldol condensation of keto esters. Hafnium-containing BEA (Hf-BEA) zeolites catalyze the condensation of ethyl pyruvate into diethyl 2-methyl-4-oxopent-2-enedioate and diethyl 2-methylene-4-oxopentanedioate (an itaconic acid ester analogue) with a selectivity of ca. 80% at ca. 60% conversion in a packed-bed reactor. The catalyst is stable for 132 h on stream, reaching a turnover number of 5110 mol[subscript EP] mol[subscript Hf]⁻¹. Analysis of the dynamic behavior of Hf-BEA under flow conditions and studies with Na-exchanged zeolites suggest that Hf(IV) open sites possess dual functionality for Lewis and Brønsted acid catalysis.United States. Department of Energy (DE-FG0212ER16352)National Science Foundation (U.S.) (122374
One-pot synthesis of MWW zeolite nanosheets using a rationally designed organic structure-directing agent
No full textA new material MIT-1 comprised of delaminated MWW zeolite nanosheets is made in a one-pot synthesis using a rationally designed organic structure-directing agent (OSDA). The OSDA consists of a hydrophilic head segment that resembles the OSDA used to synthesize the zeolite precursor MCM-22(P), a hydrophobic tail segment that resembles the swelling agent used to swell MCM-22(P), and a di-quaternary ammonium linker that connects both segments. MIT-1 features high crystallinity and surface areas exceeding 500 m[superscript 2] g[superscript −1], and can be synthesized over a wide synthesis window that includes Si/Al ratios ranging from 13 to 67. Characterization data reveal high mesoporosity and acid strength with no detectable amorphous silica phases. Compared to MCM-22 and MCM-56, MIT-1 shows a three-fold increase in catalytic activity for the Friedel–Crafts alkylation of benzene with benzyl alcohol.United States. Dept. of Energy. Office of Basic Energy Sciences. Chemical Sciences, Geosciences, & Biosciences Division (DE-FG0212ER16352)Natural Sciences and Engineering Research Council of Canada (Banting Postdoctoral Fellowship
Heterogeneous Epoxide Carbonylation by Cooperative Ion-Pair Catalysis in Co(CO)4–‑Incorporated Cr-MIL-101
No full textDespite the commercial desirability of epoxide carbonylation to β-lactones, the reliance of this process on homogeneous catalysts makes its industrial application challenging. Here we report the preparation and use of a Co(CO)₄ - -incorporated Cr-MIL-101 (Co(CO)₄ Cr-MIL-101, Cr-MIL-101 = Cr₃O(BDC)₃F, H₂BDC = 1,4-benzenedicarboxylic acid) heterogeneous catalyst for the ring-expansion carbonylation of epoxides, whose activity, selectivity, and substrate scope are on par with those of the reported homogeneous catalysts. We ascribe the observed performance to the unique cooperativity between the postsynthetically introduced Co(CO)₄ - and the site-isolated Lewis acidic Cr(III) centers in the metal-organic framework (MOF). The heterogeneous nature of Co(CO)₄ Cr-MIL-101 allows the first demonstration of gas-phase continuous-flow production of β-lactones from epoxides, attesting to the potential applicability of the heterogeneous epoxide carbonylation strategy.National Science Foundation (U.S.) (Award DMR-1452612)United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0016214
Gogol in Yuriy Lutsky's interpretation
No full textGogol is the key subject in Yuriy Lutsky's creative heritage. Yuriy Lutsky's work Between Gogol and Shevchenko was translated an d published in Ukrai e with a huge delay, almost 30 years after its first English publication in 1971 , yet one can hardly overestimate its importance for studying the Ukrainian intellectual history relating to the period of Yuriy Lutsky's linguistic and cultural development. The main problem in Lutsky's book is Gogol's linguistic, cultural, and ethnic identification. Under conditions of Ukraine's colonial dependence on Russia, the identity choice by Gogol, a great author in the verba l art , goes far beyond an individual issue and acquires much broader socio-cultura l and even political features.Тема Гоголя належить до провідних у творчому доробку Юрія Луцького. Гоголь увійшов до кола наукових інтересів ученого на певному етапі його творчого шляху, але відтоді гостре зацікавлення особистістю й творчістю великого земляка не залишало Юрія Остаповича до останніх днів життя
Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles
No full textA reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 °C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.United States. Dept. of Energy. Office of Basic Energy Sciences. Chemical Sciences, Geosciences and Biosciences Division (Grant DE-FG02-12ER16352)National Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374
Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature
No full textThe direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C–H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483–498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions.National Science Foundation (U.S.) (CHE-9808061)National Science Foundation (U.S.) (DBI-9729592
Emerging catalytic processes for the production of adipic acid
No full textResearch efforts to find more sustainable pathways for the synthesis of adipic acid have led to the introduction of new catalytic processes for producing this commodity chemical from alternative resources. With a focus on the performance of oxygen and hydrogen peroxide as preferred oxidants, this minireview summarizes recent advances made in the selective oxidation of cyclohexene, cyclohexane, cyclohexanone and n-hexane to adipic acid. Special attention is paid to the exploration of catalytic pathways involving lignocellulosic biomass-derived chemicals such as 5-hydroxymethylfurfural, D-glucose, γ-valerolactone and compounds representative of lignin and lignin-derived bio-oils.onds voor Wetenschappelijk Onderzoek--Vlaanderen (Postdoctoral Fellowship)Belgian American Educational Foundation, Inc.Fulbright Institute of International Relation
Al-MFI Nanosheets as Highly Active and Stable Catalysts for the Conversion of Propanal to Hydrocarbons
No full textArticle is dedicated to Prof. Mark E. Davis.The conversion of propanal to hydrocarbons is investigated over mesoporous aluminosilicate MFI nanosheets (Al-MFI-ns) of single-unit-cell thickness and conventional aluminum MFI zeolite (Al-MFI) at 673 K and atmospheric pressure. Al-MFI-ns exhibits a fivefold increase in stability attributed to the shorter diffusion path lengths and open architecture of the nanosheets, which minimizes pore blocking from fouling. The overall ratio of olefin to aromatic products is similar for Al-MFI-ns and Al-MFI at all conversion levels. However, the product distribution within each group shows that the Al-MFI-ns generate a fivefold increase in selectivity to C6–8 olefins and a twofold increase in selectivity to C9–10 aromatics compared to Al-MFI. The very high selectivity to C9-aromatic trimethylbenzene supports an aromatization mechanism involving sequential aldol condensation and dehydration sequences. The very short diffusion paths in the single-unit-cell thick nanosheets allows for the C9 aromatics to diffuse out of the pores before they can be converted to lighter aromatics or olefins. Al-MFI-ns shows no indication of irreversible deactivation, fully recovering its original activity after regeneration by calcination, and retaining similar deactivation rates and product selectivities as the fresh catalyst. Al-FMI-ns improves the production of aromatics from light oxygenates at mild conditions, a key feature for bio-oil upgrading.United States. Dept. of Energy (Small Business Innovation Research (SBIR) program, contract 97329S11-11
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