Yong-Wang Li

Low-temperature hydrogen production from water and methanol using Pt/α-MoC catalysts

Polymer electrolyte membrane fuel cells (PEMFCs) running on hydrogen are attractive alternative power supplies for a range of applications, with in situ release of the required hydrogen from a stable liquid offering one way of ensuring its safe storage and transportation before use. The use of methanol is particularly interesting in this regard, because it is inexpensive and can reform itself with water to release hydrogen with a high gravimetric density of 18.8 per cent by weight. But traditional reforming of methanol steam operates at relatively high temperatures (200–350 degrees Celsius), so the focus for vehicle and portable PEMFC applications has been on aqueous-phase reforming of methanol (APRM). This method requires less energy, and the simpler and more compact device design allows direct integration into PEMFC stacks. There remains, however, the need for an efficient APRM catalyst. Here we report that platinum (Pt) atomically dispersed on α-molybdenum carbide (α-MoC) enables low-temperature (150–190 degrees Celsius), base-free hydrogen production through APRM, with an average turnover frequency reaching 18,046 moles of hydrogen per mole of platinum per hour. We attribute this exceptional hydrogen production—which far exceeds that of previously reported low-temperature APRM catalysts—to the outstanding ability of α-MoC to induce water dissociation, and to the fact that platinum and α-MoC act in synergy to activate methanol and then to reform it.

Insight into CH4 Formation in Iron-Catalyzed Fischer-Tropsch Synthesis

Spin-polarized density functional theory calculations have been performed to investigate the carbon pathways and hydrogenation mechanism for CH(4) formation on Fe(2)C(011), Fe(5)C(2)(010), Fe(3)C(001), and Fe(4)C(100). We find that the surface C atom occupied sites are more active toward CH(4) formation. In Fischer-Tropsch synthesis (FTS), CO direct dissociation is very difficult on perfect Fe(x)C(y) surfaces, while surface C atom hydrogenation could occur easily. With the formation of vacancy sites by C atoms escaping from the Fe(x)C(y) surface, the CO dissociation barrier decreases largely. As a consequence, the active carburized surface is maintained. Based on the calculated reaction energies and effective barriers, CH(4) formation is more favorable on Fe(5)C(2)(010) and Fe(2)C(011), while Fe(4)C(100) and Fe(3)C(001) are inactive toward CH(4) formation. More importantly, it is revealed that the reaction energy and effective barrier of CH(4) formation have a linear relationship with the charge of the surface C atom and the d-band center of the surface, respectively. On the basis of these correlations, one can predict the reactivity of all active surfaces by analyzing their surface properties and further give guides for catalyst design in FTS.

Study on methanolytic depolymerization of PET with supercritical methanol for chemical recycling

Abstract Methanolytic depolymerization of polyethylene terephthalate (PET) was carried out in a stainless stirred autoclave at temperatures of 523–543 K, pressures of 8.5–14.0 MPa, and with a weight ratio of methanol to PET from 3 to 8. The solid products mainly composed of dimethyl terephthalate and small amounts of methyl-(2-hydroxyethyl) terephthalate, bis (hydroxyethyl) terephthalate, dimers and oligomers were analyzed by high performance liquid chromatography (HPLC). The liquid products composed of ethylene glycol and methanol were analyzed by gas chromatography (GC). It was found that both the yield of dimethyl terephthalate and the degree of PET depolymerization were seriously influenced by the temperature, weight ratio of methanol to PET, and reaction time, whilst the pressure has insignificant influence when it is above the critical point of methanol. The optimal depolymerization conditions are temperature of 533–543 K, pressure of 9.0–11.0 MPa, and the weight ratio (methanol to PET) from 6 to 8. The depolymerization of several PET wastes collected from the Chinese market was investigated under the optimal conditions.

Heterogeneous modeling for fixed-bed Fischer-Tropsch synthesis: Reactor model and its applications

Abstract A comprehensive one-dimensional heterogeneous reactor model is developed to simulate the performance of fixed-bed Fischer–Tropsch reactors for hydrocarbon production. The detailed mechanistic kinetics is combined into the reactor model along with considering the fact that the catalyst pores are filled with liquid wax under realistic conditions. The equilibrium between the gases in the bulk and the wax in the catalyst pores is correlated by using a modified SRK equation of state (MSRK EOS). The model is solved by using Gear method to integrate the reactor model with the embedded pellet model discretized by orthogonal collocation on finite elements. The validity of the reactor model is tested against the measured data from different-scale demonstration processes. Satisfactory agreements between model predictions and experiment results are obtained. Detailed numerical simulations are performed to investigate the effect of major process parameters on the reaction behavior of fixed-bed FTS systems with recycle operation.

A New Molybdenum Nitride Catalyst with Rhombohedral MoS2 Structure for Hydrogenation Applications

Nitrogen-rich transition-metal nitrides hold great promise to be the next-generation catalysts for clean and renewable energy applications. However, incorporation of nitrogen into the crystalline lattices of transition metals is thermodynamically unfavorable at atmospheric pressure; most of the known transition metal nitrides are nitrogen-deficient with molar ratios of N:metal less than a unity. In this work, we have formulated a high-pressure route for the synthesis of a nitrogen-rich molybdenum nitride through a solid-state ion-exchange reaction. The newly discovered nitride, 3R-MoN2, adopts a rhombohedral R3m structure, isotypic with MoS2. This new nitride exhibits catalytic activities that are three times more active than the traditional catalyst MoS2 for the hydrodesulfurization of dibenzothiophene and more than twice as high in the selectivity to hydrogenation. The nitride is also catalytically active in sour methanation of syngas with >80% CO and H2 conversion at 723 K. Our formulated route for the synthesis of 3R-MoN2 is at a moderate pressure of 3.5 GPa and, thus, is feasible for industrial-scale catalyst production.

Production of bioadditives from glycerol esterification over zirconia supported heteropolyacids.

The synthesis of bioadditives for biofuels from glycerol esterification with acetic acid was performed over zirconia supported heteropolyacids catalysts using H(4)SiW(12)O(40) (HSiW), H(3)PW(12)O(40) (HPW) and H(3)PMo(12)O(40) (HPMo) as active compounds. The as-prepared catalysts were characterized by N(2)-physisorption, XRD, Raman spectroscopy, NH(3)-TPD, FTIR of pyridine adsorption and H(2)O-TPD. Among the catalysts tested, HSiW/ZrO(2) achieved the best catalytic performance owing to the better combination of surface Brønsted acid sites and hydrothermal stability. A 93.6% combined selectivity of glyceryl diacetate and glyceryl triacetate with complete glycerol conversion was obtained at 120°C and 4h of reaction time in the presence of HSiW/ZrO(2). This catalyst also presented consistent activity for four consecutive reaction cycles, while HPW/ZrO(2) and HPMo/ZrO(2) exhibited distinct deactivation after reusability tests. In addition, HSiW/ZrO(2) can be resistant to the impurities present in bulk glycerol.

Support effect of Co/Al2O3 catalysts for Fischer–Tropsch synthesis☆

Abstract Cobalt supported on different γ-alumina carries prepared by incipient wetness impregnation are used to investigate the effect of support on the performance of cobalt catalysts for Fischer–Tropsch synthesis (FTS). It is found that the acidity of support has a great influence on the interaction between metallic cobalt and support and then the reducibility of cobalt. The support with low acidity leads to the higher active FTS catalysts. Furthermore, the high reducibility and more bridged type CO which is favored by γ-alumina with low acidity appears to be responsible for high C 5 + hydrocarbon selectivity and low methane selectivity.

Effect of reaction conditions on the product distribution during Fischer–Tropsch synthesis over an industrial Fe-Mn catalyst

Abstract The product distributions of Fischer–Tropsch synthesis (FTS) over an industrial Fe-Mn catalyst are investigated under different reaction conditions in an integral fixed bed reactor. The typical non-ASF distributions of the FTS products are analyzed in terms of the competitive steps of the surface reactions, and the desorption, diffusion and re-adsorption of alkenes under these broad reaction conditions. It is found that alkene selectivities are significantly higher than those for alkanes in a broad chain length range from C2 to about C20 over the Fe-Mn catalyst under most reaction conditions. Under the operation conditions of the catalyst, alkenes with carbon number larger than 27 cannot be detected in the wax products. Consequently, the contents of heavy alkanes have a slight increase at about C27, implying that primary alkenes with chain longer than C27 are dominantly hydrogenated to alkanes due to the long residence time of the products in the catalyst pores.

Highly Tunable Selectivity for Syngas-Derived Alkenes over Zinc and Sodium-Modulated Fe5C2 Catalyst

Zn- and Na-modulated Fe catalysts were fabricated by a simple coprecipitation/washing method. Zn greatly changed the size of iron species, serving as the structural promoter, while the existence of Na on the surface of the Fe catalyst alters the electronic structure, making the catalyst very active for CO activation. Most importantly, the electronic structure of the catalyst surface suppresses the hydrogenation of double bonds and promotes desorption of products, which renders the catalyst unexpectedly reactive toward alkenes-especially C5+ alkenes (with more than 50% selectivity in hydrocarbons)-while lowering the selectivity for undesired products. This study enriches C1 chemistry and the design of highly selective new catalysts for high-value chemicals.

One-step hydrogenolysis of glycerol to biopropanols over Pt–H4SiW12O40/ZrO2 catalysts

The one-step hydrogenolysis of biomass-derived glycerol to propanols (1-propanol + 2-propanol), which are known as biopropanols, was investigated over different supported Pt–H4SiW12O40 (HSiW) bi-functional catalysts in aqueous media. Among the catalysts/supports tested, Pt–HSiW supported over ZrO2 converted glycerol to biopropanols with high selectivity and high yield (94.1%), while exhibiting long-term stability (160 h). In addition, this catalyst can be resistant to the impurities present in crude glycerol. The reaction pathway to propanols from glycerol is proposed to proceed mainly through 1,2-propanediol. With the strategy toward one-step hydrogenolysis of glycerol to biopropanols sustainably, the biomass can be readily transformed to biodiesel and biopropanols via glycerol, which will bring about the benign development of the biodiesel industry.