Yingxin Liu

A New Approach Towards Acid Catalysts with High Reactivity Based on Graphene Nanosheets

Solid acid catalysts of graphene oxide and sulfonated graphene oxide nanosheets have been prepared by using the modified Hummers and sulfonation methods. Physical characterization indicated that a number of functional groups such as COOH, OH, O, and SO3H were introduced onto the surfaces of the as‐synthesized nanosheets. The catalytic performance of the synthesized catalysts was evaluated in the hydrolysis of the glycosidic bond and Fischer esterification. The experimental results indicated that the catalytic activity of the sulfonated graphene oxide was superior to that of other solid acid catalysts with the same or higher acid strength and has also exceeded that of H2SO4 with 9.1 times of acid strength than that of the sulfonated graphene oxide. The high reactivity can be ascribed to the formation of hydrophobic cavities through the combination of graphene sheet and the oxygen‐containing groups on its surface, which may facilitate the catalyst to anchor with reactants and promote the attack of protons.

Graphene-supported Pd catalyst for highly selective hydrogenation of resorcinol to 1, 3-cyclohexanedione through giant π-conjugate interactions.

The selective hydrogenation of resorcinol (RES) to 1, 3-cyclohexanedione (1,3-CHD) without the addition of alkali is a big challenge. In this article, a novel reduced graphene oxide (rGO) supported Pd catalyst was prepared through co-reduction method, over which we obtained 99.9% of resorcinol conversion and 94.2% of the ever-reported highest 1,3-cyclohexanedione selectivity at 25 °C in only CH2Cl2 solvent. The excellent selectivity was contributed to the strong π-π and p-π interactions between the graphene nanosheet and the benzene ring as well as hydroxyl in RES molecule. The followed adsorption experiment and Raman analysis also showed the existence of aromatic graphite structures in rGO, which exhibited stronger adsorption towards RES than towards 1,3-CHD.

A novel route towards high yield 5-hydroxymethylfurfural from fructose catalyzed by a mixture of Lewis and Brönsted acids

We have developed an effective route for obtaining 5-hydroxymethylfurfural with a yield of 92.6 mol% from the dehydration of fructose in N,N-dimethylformamide using a mixture of AlCl3, H2SO4 and H3PO4 as catalyst. The NMR analysis showed the intermediate formed among fructose, AlCl3 and H3PO4 plays an important role in the novel result.

An Efficient and Reusable Embedded Ru Catalyst for the Hydrogenolysis of Levulinic Acid to γ-Valerolactone

To achieve a higher activity and reusability of a Ru-based catalyst, Ru nanoparticles were embedded in N-doped mesoporous carbon through a hard-template method. The catalyst showed excellent catalytic performance (314 h-1 turnover frequency) and recyclability (reusable five times with 3 % activity loss) for the hydrogenolysis of levulinic acid to γ-valerolactone. Compared with the mesoporous carbon without N-doping and conventional activated carbon, the introduction of N-dopant effectively improved the dispersion of Ru nanoparticles, decreased the average size of Ru nanoparticles to as small as 1.32 nm, and improved the adsorption of levulinic acid, which contributed to the increase in the activity of the catalyst. Additionally, the embedding method increased the interaction between Ru nanoparticles and carbon support in contrast with the conventional impregnation method, thus preventing the Ru nanoparticles from migration, aggregation, and leaching from the carbon surface and therefore increasing the reusability of the catalyst.

One-pot production of 2,5-dimethylfuran from fructose over Ru/C and a Lewis–Brønsted acid mixture in N,N-dimethylformamide

An efficient catalysis system composed of a Lewis–Bronsted acid mixture and Ru/C using N,N-dimethylformamide as a solvent was developed for the one-pot conversion of fructose to 2,5-dimethylfuran (2,5-DMF) via the dehydration/hydrogenolysis sequence. The effects of various reaction parameters, such as solvent, catalyst type, catalyst loading, reaction pressure, temperature and time, on single fructose dehydration, 5-hydroxymethylfurfural (5-HMF) hydrogenolysis and the one-pot conversion of fructose to 2,5-DMF were systematically investigated. The results showed that 2,5-DMF could be successfully produced with a yield as high as 66.3 mol% by using a one-pot method directly from fructose under the optimized reaction conditions, which is by far the highest yield ever reported for the production of 2,5-DMF from fructose through a one-pot strategy. The Ru/C catalyst could be reused at least three times with a slight decrease in 2,5-DMF yield.

Nitrogen-Doped Graphene-Supported Iron Catalyst for Highly Chemoselective Hydrogenation of Nitroarenes

A nitrogen‐doped graphene‐supported iron catalyst was used for the first time in the hydrogenation of a series of nitroarenes to give the corresponding amines with excellent activity and chemoselectivity under mild reaction conditions. Physicochemical characterization of the catalyst by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and Mössbauer spectroscopy revealed the formation of iron particles with an iron oxide core and a metallic iron shell that were coated by a few layers of nitrogen‐doped graphene. The unique structure of FeNx/C in the catalyst was proven to contribute to the hydrogenation activity.

Novel Pd-BTP/SiO2 as an Effective Heterogeneous Catalyst for Heck Reactions

A highly efficient and reusable catalyst, palladium (II) complex supported on functionalized silica, was prepared by anchoring palladium (II) onto 2,6-bis(5,6-dimethyl-1,2,4-triazine-3-yl)pyridine [BTP]-modified mesoporous silica (labeled as Pd-BTP/SiO2). The catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer Emmett Teller (BET) analysis. Its catalytic performance was tested for the Heck coupling reactions between aryl halides with acrylic acid or styrene, and good to excellent results (higher conversions 87–96% and yields 66–78%) were obtained. The catalyst system was stable under the reaction conditions and could be successfully reused more than five times without the loss of catalytic activity.

Switchable synthesis of furfurylamine and tetrahydrofurfurylamine from furfuryl alcohol over RANEY® nickel

RANEY® Ni proved to be an effective heterogeneous catalyst for switchable reductive amination of furfuryl alcohol to tetrahydrofurfurylamine and furfurylamine with NH3 by simply adding or not adding 1.0 MPa H2 into the reaction bulk. After further optimization of the reaction conditions, we finally obtained 94.0% yield of tetrahydrofurfurylamine and 78.8% yield of furfurylamine with high selectivity. By extensively studying the catalytic pathways and mechanism of catalyst deactivation with XRD and XPS characterization, we have confirmed that an excess amount of H2 in the reaction bulk leads to the deep hydrogenation of the furan ring while an insufficient amount of H2 leads to the formation of Ni3N and the deactivation of the catalyst.