Shi-Chao Qi

Application of supported metallic catalysts in catalytic hydrogenation of arenes

Since arenes generally exist in coals and their derivatives, petroleum, crop stalks and even liquid fuels, such as gasoline and diesel, catalytic hydrogenation of arenes is a very important process both for hydroconverting fossil and biomass resources and for deeply upgrading liquid fuels. Supported metal-catalyzed hydrogenation is still the primary method for reducing arenes and heteroatomic species. Both noble and non-noble metals as well as a variety of alloys have been extensively investigated as the active species of catalysts. The catalytic activity for arene hydrogenation and the sulfur-resistance of catalysts are attributed to the nature of both metals and supports. As widely used supports, zeolites can greatly improve the sulfur-resistance and hydrogenation activity of catalysts due to their distinct channel structure and adjustable acid sites. In addition, some new processes of catalyst preparation have been created to modify the dispersion of metal particles, even to prepare supported metal nanoparticles. The thermodynamics and kinetics of arene hydrogenation have been systematically investigated as well. The hydrogenation order of each aromatic ring is judged by the superdelocalizability and the reaction order greatly depends on the nature of catalyst and the reaction conditions.

A Highly Active Ni/ZSM‐5 Catalyst for Complete Hydrogenation of Polymethylbenzenes

Highly active supported nickel catalysts (SNCs) play crucial roles in many chemical processes, such as olefin hydrogenation, cross-coupling reaction, stereoselective synthesis, electrochemistry, and biochemistry. Catalytic hydrogenation of arenes was considered to be the criterion for evaluating the activity of SNCs. For instance, methanol-to-gasoline (MTG) is an important process of energy conversion, but it normally produces substantial amount of a heavy mixture (HM), which is rich in polymethylbenzenes (PMBs). It is extremely difficult to hydrogenate PMBs, because increasing the number of methyl groups severely reduces both the equilibrium and rate constants of the hydrogenation. 6] Conventional methods of catalyst preparation, such as impregnation, co-precipitation, sol-gel, and in situ reduction, are relatively tedious and no reports have been issued on the hydrogenation of PMBs with 4–6 methyl groups. Metal carbonyls (MCs) can be decomposed to fine metal particles at elevated temperatures and are thereby ideal precursors of highly active metal particles, e.g. , NiCu surface alloys were prepared by decomposing nickel tetracarbonyl (NTC) on a copper substrate at 302 8C. Although some attempts for preparing metallic catalysts using MCs have been tried since 1980s, the preparation of SNCs, which are active enough to catalyze the hydrogenation of PMBs with 4–6 methyl groups, has not been successful, most likely because the boiling point (43 8C) of NTC is much lower than its decomposition temperature and there is a decomposition-combination equilibrium (DCE) between NTC and its decomposition products Ni and CO in a closed reactor. Herein we report a new strategy for in situ preparation of highly active SNCs by decomposing NTC at 100 8C to highly dispersive Ni onto ZSM-5. The decomposition was successively conducted to destroy the DCE by releasing the resulting CO. This strategy allows successful preparation of a highly active SNC (i.e. , Ni/ZSM-5), which exhibits dramatically high activity for the hydrogenation of benzene, toluene, durene, and HM from MTG. The operating conditions of the catalyst characterizations are detailed in the Supporting Information. As Figure 1 displays, a number of spherical particles with diameter less than 100 nm adhere to the surface of ZSM-5. The

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.

Recent application of calculations of metal complexes based on density functional theory

Density functional theory (DFT) has become a widely applied computational tool in most chemistry fields. Because of its applicability, DFT calculations involving metal complexes are reviewed. The achievements in the applications of DFT and the diverse DFT usage modes are shown. Developments of exchange–correlation functionals and weak interaction corrections are concisely illustrated. Moreover, practical applications of different functionals are compared and suggestions regarding the selection of functionals are presented. There are basically two methods of obtaining highly accurate exchange–correlation functionals, and borrowing the concept of orbitals from ab initio method is still unavoidable in DFT for the foreseeable future.

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.

Calcium oxide-modified mesoporous silica loaded onto ferriferrous oxide core: Magnetically responsive mesoporous solid strong base

The design of new type of solid strong base with ideal activity, stability, and reusability is strongly urged by the growing demand of green chemistry and sustainable development. In this study, a new type of mesoporous solid strong base, denoted as CaO/mSiO2/Fe3O4, is successfully fabricated by successively coating SiO2 onto Fe3O4 magnetic nanoparticles and loading CaO into the mesoporous SiO2. Compared with a series of other typical solid bases, the CaO/mSiO2/Fe3O4 exhibits higher activity towards the synthesis of dimethyl carbonate by the transesterification of ethylene carbonate and methanol. The activity of the CaO/mSiO2/Fe3O4 is not observed to decrease obviously even after sextic catalyst recirculation, and in particular, the recovery of the catalyst without quality loss is very convenient due to the good magnetic responsiveness of the Fe3O4 cores.

Potassium-incorporated mesoporous carbons: strong solid bases with enhanced catalytic activity and stability

With the growing demand for green chemistry, mesoporous solid strong bases have attracted increasing attention in view of their tremendous potential as eco-friendly catalysts in diverse reactions. In the present study, K-incorporated mesoporous carbon is successfully prepared through high-temperature chemical activation combined with the hard-templating method. The combined method is proved to be very effective at promoting the formation of stable K species that strongly interact with the carbon support. The obtained solid bases thus have both high activity and enhanced water-resistant stability, which is reflected in their catalysis of the transesterification of ethylene carbonate with methanol to dimethyl carbonate. A much higher turnover frequency (TOF) value (430.4 h−1) and better reusability are thus observed, compared with a series of typical and popular solid bases, such as MgO (TOF, 1.0 h−1) and CaO/SBA-15 (TOF, 6.4 h−1).

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.