Mechanisms of hydrodesulfurization and hydrodenitrogenation

Review of Theoretical and Computational Studies of Bulk and Single Atom Catalysts for H2 S Catalytic Conversion

Catalytic conversion of hydrogen sulfide (H2 S) plays a vital role in environmental protection and safety production. In this review, recent theoretical advances for catalytic conversion of H2 S are systemically summarized. Firstly, different mechanisms of catalytic conversion of H2 S are elucidated. Secondly, theoretical studies of catalytic conversion of H2 S on surfaces of metals, metal compounds, and single-atom catalysts (SACs) are systematically reviewed. In the meantime, various strategies which have been adopted to improve the catalytic performance of catalysts in the catalytic conversion of H2 S are also reviewed, mainly including facet morphology control, doped heteroatoms, metal deposition, and defective engineering. Finally, new directions of catalytic conversion of H2 S are proposed and potential strategies to further promote conversion of H2 S are also suggested: including SACs, double atom catalysts (DACs), single cluster catalysts (SCCs), frustrated Lewis pairs (FLPs), etc. The present comprehensive review can provide an insight for the future development of new catalysts for the catalytic conversion of H2 S.

The influence of activation atmosphere on the active phase and hydrotreating activity of LDH-based NiW pre-sulfurized catalysts

Activation atmosphere and temperature determined active phases of NiW pre-sulfurized hydrotreating catalysts prepared via a tetrathiotungstate intercalated NiAl layered double hydroxide.

Di- and Tetrameric Molybdenum Sulfide Clusters Activate and Stabilize Dihydrogen as Hydrides

NaY zeolite-encapsulated dimeric (Mo₂S₄) and tetrameric (Mo₄S₄) molybdenum sulfide clusters stabilize hydrogen as hydride binding to Mo atoms. Density functional theory (DFT) calculations and adsorption measurements suggest that stabilization of hydrogen as sulfhydryl (SH) groups, as typical for layered MoS₂, is thermodynamically disfavored. Competitive adsorption of H₂ and ethene on Mo was probed by quantifying adsorbed CO on partly hydrogen and/or ethene covered samples with IR spectroscopy. During hydrogenation, experiment and theory suggest that Mo is covered predominately with ethene and sparsely with hydride. DFT calculations further predict that, under reaction conditions, each Mo _x S _y cluster can activate only one H₂, suggesting that the entire cluster (irrespective of its nuclearity) acts as one active site for hydrogenation. The nearly identical turnover frequencies (24.7 ± 3.3 mol_ethane·h^-1·mol_cluster ^-1), apparent activation energies (31-32 kJ·mol^-1), and reaction orders (∼0.5 in ethene and ∼1.0 in H₂) show that the active sites in both clusters are catalytically indistinguishable.

Hydrogenation of Pyridine and Hydrogenolysis of Piperidine overγ-Mo2N Catalyst: A DFT study

Increasing demands on producing environmentally friendly products are becoming a driving force for designing high active catalysts. Thus, surfaces that efficiently catalyse the nitrogen reduction reactions are vastly sought in moderating air-pollutant emissions. This contribution aims to computationally investigate the hydrodenitrogenation (HDN) networks of pyridine over γ-Mo2N(111) surface via density functional theory (DFT) approach. Various adsorption configurations have been considered for the molecularly adsorbed pyridine. Findings indicate that pyridine can be adsorbed via side-on and end-on modes in six geometries in which one adsorption site is revealed to have the lowest adsorption energy of (-45.3 kcal/mol(. Over nitrogen hollow site adsorption site, initial HDN steps proceed by the stepwise hydrogenation of pyridine into piperidine followed the Langmuir−Hinshelwood mechanism. The obtained findings are the first to theoretically model the hydrogenation pathways of pyridine to form piperidine then the hydrogenolysis of piperidine producing C5H12 and NH3 over metal nitride and paved the way for further investigations to better understanding such an important nitrogen removal reactions.

Hydrotreating of Jatropha-derived Bio-oil over Mesoporous Sulfide Catalysts to Produce Drop-in Transportation Fuels

The bio-oil was largely produced by thermal pyrolysis of Jatropha-derived biomass wastes (denoted as Jatropha bio-oil) using a pilot plant with a capacity of 20 kg h-1 at Thailand Institute of Scientific and Technological Research (TISTR), Thailand. Jatropha bio-oil is an unconventional type of bio-oil, which is mostly composed of fatty acids, fatty acid methyl esters, fatty acid amides, and derivatives, and consequently, it contains large amounts of heteroatoms (oxygen ~20 wt.%, nitrogen ~ 5 wt.%, sulfur ~ 1000 ppm.). The heteroatoms, especially nitrogen, are highly poisonous to the metal or sulfide catalysts for upgrading of Jatropha bio-oil. To overcome this technical problem, we reported a stepwise strategy for hydrotreating of 100 wt.% Jatropha bio-oil over mesoporous sulfide catalysts (CoMo/γ-Al2O3 and NiMo/γ-Al2O3) to produce drop-in transport fuels, such as gasoline- and diesel-like fuels. This study is very different from our recent work on co-processing of Jatropha bio-oil (ca. 10 wt.%) with petroleum distillates to produce a hydrotreated oil as a diesel-like fuel. Jatropha bio-oil was pre-treated through a slurry-type high-pressure reactor under severe conditions, resulting in a pre-treated Jatropha bio-oil with relatively low amounts of heteroatoms (oxygen < 20 wt.%, nitrogen < 2 wt.%, sulfur < 500 ppm.). The light and middle distillates of pre-hydrotreated Jatropha bio-oil were then separated by distillation at a temperature below 240 °C, and a temperature of 240–360 °C. Deep hydrotreating of light distillates over sulfide CoMo/γ-Al2O3 catalyst was performed on a batch-type high-pressure reactor at 350 °C and 7 MPa of H2 gas for 5 h. The hydrotreated oil was a gasoline-like fuel, which contained 29.5 vol.% of n-paraffins, 14.4 vol.% of iso-paraffins, 4.5 vol.% of olefins, 21.4 vol.% of naphthene compounds and 29.6 wt.% of aromatic compounds, and little amounts of heteroatoms (nearly no oxygen and sulfur, and less than 50 ppm of nitrogen), corresponding to an octane number of 44, and it would be suitable for blending with petro-gasoline. The hydrotreating of middle distillates over sulfide NiMo/γ-Al2O3 catalyst using the same reaction condition produced a hydrotreating oil with diesel-like composition, low amounts of heteroatoms (no oxygen and less than 50 ppm of sulfur and nitrogen), and a cetane number of 60, which would be suitable for use in drop-in diesel fuel.

Catalytic upgrading of bio-oil produced from hydrothermal liquefaction of Nannochloropsis sp

Upgrading of bio-oil obtained from hydrothermal liquefaction (HTL) of algae is necessary for it to be used as a fuel. In this study, bio-oil obtained from HTL of Nannochloropsis sp. was upgraded using five different catalysts (Ni/C, ZSM-5, Ni/ZSM-5, Ru/C and Pt/C) at 300 °C and 350 °C. The upgraded bio-oil yields were higher at 300 °C; however, higher quality upgraded bio-oils were obtained at 350 °C. Ni/C gave the maximum upgraded bio-oil yield (61 wt%) at 350 °C. However, noble metal catalysts (Ru/C and Pt/C) gave the better upgraded bio-oils in terms of acidity, heating values, and nitrogen values. The higher heating value of the upgraded bio-oils ranged from 40 to 44 MJ/kg, and the nitrogen content decreased from 5.37 to 1.29 wt%. Most of the upgraded bio-oils (35-40 wt%) were in the diesel range. The major components present in the gaseous products were CH₄, CO, CO₂ and lower alkanes.

Modeling the active sites of Co-promoted MoS2 particles by DFT

The atomic-scale structure of the Co-promoted MoS₂ catalyst (CoMoS), used for hydrodesulfurization and as a potential replacement for platinum in the acidic hydrogen evolution reaction has been analyzed by modeling its sites using density functional theory and applying thermochemical corrections to account for different reaction conditions. The equilibrium structures of the edges, basal plane and corners have been found and used to obtain a picture of an ideal CoMoS nanoparticle under hydrodesulfurization and hydrogen evolution reaction conditions. Under hydrodesulfurization conditions small energy differences between structures having an additional or missing sulfur atom relative to the equilibrium structures have been observed for the edges and corners explaining their activity towards hydrodesulfurization at the atomic scale. The lack of these small energy differences at the basal plane explains why it is inert towards hydrodesulfurization. The adsorption free energy of hydrogen was calculated and used as a descriptor for qualifying each site in the context of hydrogen evolution, finding that the corner site should perform better than the edges.

Metal-Organic Frameworks as a Potential Platform for Selective Treatment of Gaseous Sulfur Compounds

The release of various anthropogenic pollutants such as gaseous sulfur compounds into the environment has been accelerated as globalization has promoted the production of high-quality products at lower prices. Because of strict enforcement of mitigation technologies, advanced materials have been developed to efficiently remove gaseous sulfur compounds released from various source processes. Metal-organic frameworks (MOFs) are promising materials to treat sulfur compounds via adsorption, catalysis, or separation. Nonetheless, the practical applicability of MOFs is limited by a number of factors including loss of structural integrity after use, limited reusability of spent MOFs, and low stability toward omnipresent molecules (e.g., H₂O). Here, we provide a comprehensive assessment of MOF technology for the effective control of gaseous sulfur compounds. This review will thus help expand the fields of real-world application for MOFs with a roadmap for this highly challenging area of research.

Adsorption of quinoline from liquid hydrocarbons on graphite oxide and activated carbons

Graphite oxide might be a promising adsorbent for adsorption denitrogenation due to its significant amount of oxygen functional groups.

Reactivity of Alkyldibenzothiophenes Using Theoretical Descriptors

Theoretical calculations of the reactivity of dibenzothiophene and its methyl, dimethyl, and trimethyl derivatives show that local reactivity descriptors reproduce their experimental desulfurization reactivity trend if the first desulfurization step involves directly the sulfur atom, which only occurs if the sulfur atom is blocked at most by one methyl group. In the series of molecules{4,7-dimethyldibenzothiophene,x,4,7-trimethyldibenzothiophene (x=1,2,3)}, the most reactive molecule is 2,4,7-trimethyldibenzothiophene, and local descriptors show that the reactivity is linked to the activity of the sulfur atom, which is higher in 2,4,7-trimethyldibenzothiophene due to the position of the third methyl substitute, located in theparaposition with respect to the carbon bonded to the sulfur atom. The electrostatic potential of 2,4,7-trimethyldibenzothiophene shows one effective adsorption site, while 1,4,7-trimethyldibenzothiophene and 3,4,7-trimethyldibenzothiophene have more sites, contributing to the higher reactivity of 2,4,7-trimethyldibenzothiophene. The index of reactivity of other descriptors was evaluated and the effect of the position of the methyl substituents on adsorption parameters, as the dipole moment and the atomic charges were also studied.

Dipalladium(I) terphenyl diphosphine complexes as models for two-site adsorption and activation of organic molecules

A para-terphenyl diphosphine was employed to support a dipalladium(I) moiety. Unlike previously reported dipalladium(I) species, the present system provides a single molecular hemisphere for binding of ligands across two metal centers, enabling the characterization and comparison of the binding of a wide variety of saturated and unsaturated organic molecules. The dipalladium(I) terphenyl diphosphine toluene-capped complex was synthesized from a dipalladium(I) hexaacetonitrile precursor in the presence of toluene. The palladium centers display interactions with the π-systems of the central ring of the terphenyl unit and that of the toluene. Exchange of toluene for anisole, 1,3-butadiene, 1,3-cyclohexadiene, thiophenes, pyrroles, or furans resulted in well-defined π-bound complexes which were studied by crystallography, nuclear magnetic resonance (NMR) spectroscopy, and density functional theory. Structural characterization shows that the interactions of the dipalladium unit with the central arene of the diphosphine does not vary significantly in this series allowing for a systematic comparison of the binding of the incoming ligands to the dipalladium moiety. Several of the complexes exhibit rare μ-η(2):η(2) or μ-η(2):η(1)(O or S) bridging motifs. Hydrogenation of the thiophene and benzothiophene adducts was demonstrated to proceed at room temperature. The relative binding strength of the neutral ligands was determined by competition experiments monitored by NMR spectroscopy. The relative equilibrium constants for ligand substitution span over 13 orders of magnitude. This represents the most comprehensive analysis to date of the relative binding of heterocycles and unsaturated ligands to bimetallic sites. Binding interactions were computationally studied with electrostatic potentials and molecular orbital analysis. Anionic ligands were also demonstrated to form π-bound complexes.

Future Refining Catalysis - Introduction of Biomass Feedstocks

Refining catalysis has been developing over many years to satisfy the demand for high-quality and environmentally-acceptable automotive fuels. Biomass-derived feedstocks have been recently introduced into refineries posing thus new challenges for refining processes and catalysis. The manuscript focuses on three prominent biomass-derived feedstocks: triglycerides, bio-oils and Fischer-Tropsch products from gasified biomass. Due to high oxygen content in biomass feedstocks, deoxygenation processes play an important role in upgrading of these feedstocks. Thus, first peculiarities of deoxygenation are discussed in detail in the context of hydrotreatment processes. Different possibilities of triglycerides and bio-oils deoxygenation including their coprocessing with crude-oil-derived fractions are described. Since biomass-to-liquid processes are very important for the conversion of general biomass into liquid products, the second part deals with the aspects of biomass conversion to synthesis gas, Fischer-Tropsch synthesis and introduction of new co-catalysts.