Shinji Kudo

Efficient levoglucosenone production by catalytic pyrolysis of cellulose mixed with ionic liquid

Levoglucosenone is a synthetically valuable and versatile compound that is present as a minor product of cellulose pyrolysis. Here, we report the catalytic pyrolysis of cellulose by mixing with 1-butyl-2,3-dimethylimidazolium triflate ionic liquid (IL), forming levoglucosenone in high yield. The catalysis of the IL was selectively directed to form levoglucosenone, while the low content of IL (50%) effectively prevented formation of char, leading to a yield near 20% even at 250 °C. The thermally stable IL could be fully recovered from the mixture pyrolyzed up to 300 °C and reutilized for pyrolysis.

Theoretical Study on Reaction Pathways Leading to CO and CO2 in the Pyrolysis of Resorcinol

Possible pathways for the pyrolysis of resorcinol with the formation of CO and CO2 as final products were proposed and evaluated using ab initio calculations. Our experimental study revealed that large quantities of CO2 are generated in the pyrolysis of 1,3-dihydroxybenzene (resorcinol), while the pyrolysis of the dihydroxybenzene isomers 1,2-dihydroxybenzene (catechol) and 1,4-dihydroxybenzene (hydroquinone) produces little CO2. The fate of oxygen atoms in catechol and hydroquinone was essentially the formation of CO. In the proposed pathways, the triplet ground state m-benzoquinone was generated initially from simultaneous cleavage of the two O-H bonds in resorcinol. Subsequently, the direct cleavage of a C-C bond of the m-benzoquinone diradical yields 2-oxidanylcyclopenta-2,4-dien-1-yl-methanone, which can be converted via two channels: release of CO from the aldehyde radical group and combination of the ketone radical and carbon atom in the aldehyde radical group to form the 6-oxabicyclo[3.2.0]hepta-2,4-dien-7-one, resulting in the release of CO2. Potential energy surfaces along the proposed reaction pathways were calculated employing the CBS-QB3 method, and the rate constants at the high-pressure limit were also evaluated based on transition-state theory to assess the feasibility of the proposed reaction pathways.

Nano-sized nickel catalyst for deep hydrogenation of lignin monomers and first-principles insight into the catalyst preparation

This paper reports, for the first time, complete arene hydrogenation of phenolic compounds as lignin monomers over a non-noble metal catalyst supported by a general material. A type of nano-sized Ni catalyst was prepared in ethanol and in situ supported by ZSM-5 zeolite through general borohydride reduction of Ni2+ to Ni0, but with application of a simple ligand, pyridine. This catalyst showed an activity so high as to completely or near completely hydrogenate the aromatic rings of phenol and its twelve derivatives as potential lignin monomers at 180 °C. The activity was clearly higher than that of another type of conventional Ni catalyst prepared in the absence of pyridine. Analyses of the catalysts by TEM/EDS, XPS, XAFS and others demonstrated that pyridine had crucial roles in selective formation of nano-sized Ni and maintenance of its activity by appropriate interaction with the support. This paper also shows our theoretical approach to the mechanism of the borohydride reduction. First-principles calculations based on density functional theory (DFT) revealed the reaction pathway from Ni2+ to Ni0 and the role of pyridine, which was validated by some experimental facts. The DFT calculations also explain the variety of reactivities of the lignin monomers, which are strongly influenced by their molecular electrostatic and steric nature.

Catalytic hydrogenolysis of kraft lignin to monomers at high yield in alkaline water

Inspired by the results of calculation on the basis of density functional theory and a semi-empirical method, we found an easy, robust, and efficient approach to solve the problem of folded lignin macromolecules, which is a key factor for impeding their breakdown into monomers by hydrogenolysis. Oxidation and hydrogenolysis, which appear to be independent and contradictory of each other in many past studies, were combined and successively performed in this study. Hydrogen peroxide was used to damage the strong intramolecular hydrogen bonds of kraft lignin efficiently, transforming the folded three-dimensional geometries of the lignin macromolecules into stretched ones in an alkaline aqueous medium. Following the pretreatment of stretching lignin molecules, catalytic hydrogenolysis was performed in the presence of a Ni catalyst supported by the ZSM-5 zeolite, reported by the authors. Because of more chemisorption sites of the stretched lignin macromolecules onto the catalyst surface and the remission of lignin re-polymerization/self-condensation, conversion of the kraft lignin into oil reached 83 wt% lignin, 91 wt% which was accounted for by nine types of monomers. This study has thus demonstrated high yield monomer production from lignin dissolved in aqueous media.

Theoretical Study on Elementary Reaction Steps in Thermal Decomposition Processes of Syringol-Type Monolignol Compounds

This paper theoretically investigated a large number of reaction pathways and kinetics to describe the vapor-phase pyrolytic behavior of several syringol-type monolignol compounds that are derived from the primary pyrolysis of lignin: 1-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-en-1-one (HDPP), sinapyl alcohol, 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)propan-1-one (HHDPP), 1-(4-hydroxy-3,5-dimethoxyphenyl)propane-1,3-diol (HDPPD), and syringol. The possible pyrolytic pathways involving unimolecular decomposition, addition, and abstraction reactions were investigated by comparing the energy barriers calculated at the B3LYP/6-311++G(d,p) level. In the proposed pathways, all syringol-type monolignols containing a side chain undergo its cleavage to form syringol through the formation of syringaldehyde or 4-vinylsyringol. Syringol is then converted into two products: (a) pyrogallol via the homolysis of the O-CH3 bond and hydrogenation or (b) guaiacol via addition of an H atom with a carbon bearing methoxyl group in syrignol and the subsequent demethoxylation. The pyrolytic pathways of pyrogallol are classified into two processes: (a) the concerted dehydrogenation of the two hydroxyl H atoms and the unimolecular decomposition to produce acetylene (C2H2), ethynol (C2HOH), and CO or (b) the displacement of an OH with H to produce catechol and resorcinol. Additionally, HDPP undergoes O-CH3 bond cleavage to form but-1-en-3-yne. The high-pressure limit rate constants for all the proposed elementary reaction steps were evaluated on the basis of transition state theory.

Theoretical Study on the Kinetics of Thermal Decomposition of Guaiacol and Catechol

The theoretical aspects of the development of a chemical kinetic model for guaiacol and catechol pyrolysis are presented to describe the pyrolysis behaviors of the individual lignin-derived components. The possible pyrolysis pathways involving both unimolecular and bimolecular decomposition were investigated by the potential energy surfaces (PES) calculated at CBS-QB3 level. The high-pressure limiting rate constants of each elementary reaction step were evaluated based on the transition state theory (TST) to determine the dominant pyrolysis pathways. The kinetic analysis results predicted the most favorable catechol unimolecular decomposition pathways, where catechol isomerization to 2-hydroxycyclohexa-2,4-dien-1-one occurred via migration of the hydroxyl H atom, followed by decomposition into 1,3-cyclobutadiene, acetylene, and CO. In the case of the bimolecular reaction of catechol, a hydrogen radical is coupled to the carbon atom in the benzene ring, leading to the formation of phenol and a hydroxyl radical through dehydroxylation. On the other hand, guaiacol is likely to form catechol and phenol via the O-CH3 homolysis and coupling of a hydrogen radical to the carbon atom with the methoxyl group, respectively.

An Overview of Metal Oxide Nanostructures

Abstract The goal of this chapter is to provide an overview of metal oxide nanostructures. A comprehensive literature survey of nanometal oxides has been done and is presented here. Metal oxide nanostructures have attracted substantial research interest, mainly because of their unique characteristics at nano dimensions compared to those of bulk or single-particle species. Generally, the distinctive electronic structure defines the specific metallic, semiconductor, or insulator characteristics of metal oxide nanomaterials. Methods of synthesis are categorized based on the processes involved in nanoparticle formation and are broadly classified as either bottom-up or top-down. Most of the commonly investigated top-down and bottom-up methodologies for synthesis of metal oxide nanostructures are comprehensively discussed in the following sections. Nanoparticles fabricated via the bottom-up method are built atom by atom, molecule by molecule, or cluster by cluster. It will be seen that the complex and fine nanostructures fabricated via the bottom-up methods are difficult to achieve by the usual top-down processes.

Nanomaterials as Catalysts

Abstract Nanocatalysts, which are those bridging the homogenous and heterogeneous catalysis, have been extensively explored in most catalytic reactions. This chapter solely intends to present commonly investigated classifications of nanocatalysts and their applications. The magical characteristic changes occurred at nano size have attracted researchers across the globe, which reflects the huge number of publications and patents in the field of nanoscience and nanotechnology. The unique characteristics of nanocatalysts are generally attributed to the greater number of surface atoms relative to those inside. Consequently, the surface area of nanocatalysts holds a significant role in determining their catalytic performance. Almost all transition metals have been explored to investigate their catalytic performance. In terms of improving catalytic performance, naked monometallic, bimetallic, and multimetallic nanomaterials and those reinforced with porous and stable supports have been well investigated. The multimetallic nanocatalysts exhibit multiple functionalities and stable support, providing additional stability for nanomaterials from sintering and deactivation.

Correction: Catalytic hydrogenolysis of kraft lignin to monomers at high yield in alkaline water

Correction for ‘Catalytic hydrogenolysis of kraft lignin to monomers at high yield in alkaline water’ by Shi-Chao Qi et al., Green Chem., 2017, 19, 2636–2645.