As the oil reserves are depleting the need of an alternative fuel source is becoming increasingly apparent. One prospective method for producing fuels in the future is conversion of biomass into bio-oil and then upgrading the bio-oil over a catalyst, this method is the focus of this review article. Bio-oil production can be facilitated through flash pyrolysis, which has been identified as one of the most feasible routes. The bio-oil has a high oxygen content and therefore low stability over time and a low heating value. Upgrading is desirable to remove the oxygen and in this way make it resemble crude oil. Two general routes for bio-oil upgrading have been considered: hydrodeoxygenation (HDO) and zeolite cracking. HDO is a high pressure operation where hydrogen is used to exclude oxygen from the bio-oil, giving a high grade oil product equivalent to crude oil. Catalysts for the reaction are traditional hydrodesulphurization (HDS) catalysts, such as Co–MoS2/Al2O3, or metal catalysts, as for example Pd/C. However, catalyst lifetimes of much more than 200 h have not been achieved with any current catalyst due to carbon deposition. Zeolite cracking is an alternative path, where zeolites, e.g. HZSM-5, are used as catalysts for the deoxygenation reaction. In these systems hydrogen is not a requirement, so operation is performed at atmospheric pressure. However, extensive carbon deposition results in very short catalyst lifetimes. Furthermore a general restriction in the hydrogen content of the bio-oil results in a low H/C ratio of the oil product as no additional hydrogen is supplied. Overall, oil from zeolite cracking is of a low grade, with heating values approximately 25% lower than that of crude oil. Of the two mentioned routes, HDO appears to have the best potential, as zeolite cracking cannot produce fuels of acceptable grade for the current infrastructure. HDO is evaluated as being a path to fuels in a grade and at a price equivalent to present fossil fuels, but several tasks still have to be addressed within this process. Catalyst development, understanding of the carbon forming mechanisms, understanding of the kinetics, elucidation of sulphur as a source of deactivation, evaluation of the requirement for high pressure, and sustainable sources for hydrogen are all areas which have to be elucidated before commercialisation of the process.

A review of catalytic upgrading of bio-oil to engine fuels

The incentive for use of renewable resources to replace fossil sources is motivating extensive research on new and alternative fuels derived from biomass. Bio-oils derived from cellulosic biomass offer the prospect of becoming a major feedstock for production of fuels and chemicals, and lignin is a plentiful, underutilized component of cellulosic biomass. Lignin conversion requires depolymerization and removal of oxygen. Likely processes for lignin conversion involve depolymerization (e.g., by pyrolysis) and catalytic upgrading of the resultant bio-oils. A major goal of the upgrading is catalytic hydrodeoxygenation (HDO), which involves reactions with hydrogen that produce hydrocarbons and water. The aim of this review is to present a critical introduction to HDO chemistry focused on compounds derived from lignin, including a summary of HDO reactions and those that accompany them, with a comparison of catalysts addressing their activities, selectivities, and stabilities. The reactions are evaluated in terms of reaction pathways of compounds representative of lignin-derived bio-oils, including anisole, guaiacol, and phenol. The review includes recommendations for further research and an attempt to place HDO in a context of options for renewable fuels and chemicals, but it does not provide an economic assessment.

Upgrading of lignin-derived bio-oils by catalytic hydrodeoxygenation

Carbon nanotubes are promising materials for various applications. In recent years, progress in manufacturing and functionalizing carbon nanotubes has been made to achieve the control of bulk and surface properties including the wettability, acid–base properties, adsorption, electric conductivity and capacitance. In order to gain the optimal benefit of carbon nanotubes, comprehensive understanding on manufacturing and functionalizing carbon nanotubes ought to be systematically developed. This review summarizes methodologies of manufacturing carbon nanotubes via arc discharge, laser ablation and chemical vapor deposition and functionalizing carbon nanotubes through surface oxidation and activation, doping of heteroatoms, halogenation, sulfonation, grafting, polymer coating, noncovalent functionalization and nanoparticle attachment. The characterization techniques detecting the bulk nature and surface properties as well as the effects of various functionalization approaches on modifying the surface properties for specific applications in catalysis including heterogeneous catalysis, photocatalysis, photoelectrocatalysis and electrocatalysis are highlighted.

Carbon nanotube catalysts: recent advances in synthesis, characterization and applications.

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Single-Atom Catalysts across the Periodic Table.

As two coexisting and fast-growing research fields in modern synthetic chemistry, the merging of organocatalysis and C–H bond functionalization is well foreseeable, and the joint force along this line has been demonstrated to be a powerful approach in making inert C–H bond functionalization more viable, predictable, and selective. In this review, we provide a comprehensive summary of organocatalysis in inert C–H bond functionalization over the past two decades. The review is arranged by types of inert C–H bonds including alkane C–H, arene C–H, and vinyl C–H as well as those activated benzylic C–H, allylic C–H, and C–H bonds alpha to the heteroatom such as nitrogen and oxygen. In each section, the discussion is classified by the explicit organocatalytic mode involved.

Organocatalysis in Inert C–H Bond Functionalization

A series of metal-free N-doped carbon nanotubes (CNTs) are fabricated using an in-situ synthesis and post nitridation treatment. N-doped carbon nanotubes with various defects, nitrogen contents, and nitrogen species are employed as the catalysts for nitrobenzene hydrogenation. The potential active sites of N-doped carbon nanotubes are explored in terms of catalytic performance in nitrobenzene hydrogenation as well as DFT calculations of hydrogen adsorption on carbon nanotubes and nitrogen species. Active and selective hydrogenation of nitrobenzene is achieved over N-doped carbon nanotubes prepared by post nitridation. Pyrrolic-N in the N-doped carbon nanotubes is found to play an active site for nitrobenzene hydrogenation, which is greatly in favor of the chemisorption and dissociation of hydrogen molecules. N-doped carbon nanotubes with pyrrolic-N show an encouraging catalytic hydrogenation activity in nitrobenzene reduction. These findings provide a promising route for the rational design of the metal-free hydrogenation catalysts and the development of carbon nanotube-based materials.

Nitrogen-doped carbon nanotubes as a highly active metal-free catalyst for nitrobenzene hydrogenation

A theoretical model for droplet breakup in turbulent dispersions

A BiVO4 film photoanode with re-annealing treatment and 2D thin Ti3C2TX flakes decoration for enhanced photoelectrochemical water oxidation

Non-noble nickel catalysts have been widely studied and tried in hydrogenation, however the problem of nickel particle sintering is more and more common in high-loaded nickel catalysts. A series of highly dispersed bimetallic Ni-M/AC (M = Cu, Co, Fe or Zn) catalysts were prepared by incipient wetness impregnation methods and applied in 1-nitronaphthalene hydrogenation to 1-naphthylamine under mild reaction conditions. The prepared catalysts were characterized by XRD, BET, H2-TPR, TEM, HRTEM, HAADF-STEM, XPS, ICP, FT-IR and H2 chemisorption. The results show that the introduction of the metal promoter inhibits the sintering of the nickel and enhances the reducibility of the catalysts, leading to higher ratio of effective Ni° on the surface of the support, especially for Ni-Zn/AC sample. Moreover, the results of XPS indicate that the electron donating effect of Cu promoter increases surface electronic density of Ni, as a result, the electron-rich Ni might be produced because of the interfacial electronic effect, which favors the desorption and further impedes the hydrogenation of N-naphthylhydroxylamine. Ni-Zn/AC-350 with smaller nickel particles, better dispersion and larger content of effective Ni° presents the best catalytic performance in 1-nitronaphthalene hydrogenation to 1-naphthylamine under mild reaction conditions, it gives 100% conversion of 1-nitronaphthalene and 96.82% selectivity to 1-naphthylamine under 0.6 MPa and 90℃ for 5 h. Additionally, superior performances are also obtained in hydrogenation reactions of nitrobenzene, chloronitrobenzene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene over Ni-Zn/AC catalysts. With good hydrogenation activity the catalyst shows, the application prospect in industrial production of aromatic amine from aromatic nitro compounds has been becoming more and more extension.

Activated carbon supported bimetallic catalysts with combined catalytic effects for aromatic nitro compounds hydrogenation under mild conditions

Hydrotalcite-derived Co-MgAlO mixed metal oxides as efficient and stable catalyst for the solvent-free selective oxidation of cyclohexane with molecular oxygen

He’an Luo

Papers

Nitrogen-doped carbon nanotubes as a highly active metal-free catalyst for nitrobenzene hydrogenation

A theoretical model for droplet breakup in turbulent dispersions

A BiVO4 film photoanode with re-annealing treatment and 2D thin Ti3C2TX flakes decoration for enhanced photoelectrochemical water oxidation

Activated carbon supported bimetallic catalysts with combined catalytic effects for aromatic nitro compounds hydrogenation under mild conditions

Hydrotalcite-derived Co-MgAlO mixed metal oxides as efficient and stable catalyst for the solvent-free selective oxidation of cyclohexane with molecular oxygen