Xinli Zhu

A fluid-dynamic model for flow pattern on a distillation tray

Abstract A fluid–dynamic model for describing the liquid-phase flow on a sieve tray with consideration of both the resistance and the bubbling effect created by the uprising vapor phase is presented, and solved numerically by the method of control volume. For verifying the proposed model, the liquid velocity distributions on a sieve tray were measured by the hot-film anemometry. The theoretical predictions by present model are in agreement with the experimental results by the authors and from the literature.

Insights into the Major Reaction Pathways of Vapor‐Phase Hydrodeoxygenation of m‐Cresol on a Pt/HBeta Catalyst

Conversion of m‐cresol was studied on a Pt/HBeta catalyst at 225–350 °C and ambient hydrogen pressure. At 250 °C, the reaction proceeds through two major reaction pathways: (1) direct deoxygenation to toluene (DDO path); (2) hydrogenation of m‐cresol to methylcyclohexanone and methylcyclohexanol on Pt, followed by fast dehydration on Brønsted acid sites (BAS) to methylcyclohexene, which is either hydrogenated to methylcyclohexane on Pt or ring‐contracted to dimethylcyclopentanes and ethylcyclopentane on BAS (HYD path). The initial hydrogenation is the rate‐determining step of the HYD path as its rate is significantly lower than those of subsequent steps. The apparent activation energy of the DDO path is 49.7 kJ mol−1 but the activation energy is negative for the HYD path. Therefore, higher temperatures lead to the DDO path becoming the dominant path to toluene, whereas the HYD path, followed by fast equilibration to toluene, is less dominant, owing to the inhibition of the initial hydrogenation of m‐cresol.

Direct C–C Coupling of CO2 and the Methyl Group from CH4 Activation through Facile Insertion of CO2 into Zn–CH3 σ-Bond

Conversion of CO2 and CH4 to value-added products will contribute to alleviating the green-house gas effect but is a challenge both scientifically and practically. Stabilization of the methyl group through CH4 activation and facile CO2 insertion ensure the realization of C-C coupling. In the present study, we demonstrate the ready C-C coupling reaction on a Zn-doped ceria catalyst. The detailed mechanism of this direct C-C coupling reaction was examined based on the results from density functional theory calculations. The results show that the Zn dopant stabilizes the methyl group by forming a Zn-C bond, thus hindering subsequent dehydrogenation of CH4. CO2 can be inserted into the Zn-C bond in an activated bent configuration, with the transition state in the form of a three-centered Zn-C-C moiety and an activation barrier of 0.51 eV. The C-C coupling reaction resulted in the acetate species, which could desorb as acetic acid by combining with a surface proton. The formation of acetic acid from CO2 and CH4 is a reaction with 100% atom economy, and the implementation of the reaction on a heterogeneous catalyst is of great importance to the utilization of the greenhouse gases. We tested other possible dopants including Al, Ga, Cd, In, and Ni and found a positive correlation between the activation barrier of C-C coupling and the electronegativity of the dopant, although C-H bond activation is likely the dominant reaction on the Ni-doped ceria catalyst.

Effects of gap and elevated pressure on ethanol reforming in a non-thermal plasma reactor

Production of hydrogen for fuel cell vehicles, mobile power generators and for hydrogen-enhanced combustion from ethanol is demonstrated using energy-efficient non-thermal plasma reforming. A tubular reactor with a multipoint electrode system operated in pulsed mode was used. Complete conversion can be achieved with high selectivity (based on ethanol) of H2 and CO of 111% and 78%, respectively, at atmospheric pressure. An elevated pressure of 15 psig shows improvement of selectivity of H2 and CO to 120% and 87%, with a significant reduction of C2Hx side products. H2 selectivity increased to 127% when a high ratio (29.2) of water-to-ethanol feed was used. Increasing CO2 selectivity is observed at higher water-to-ethanol ratios indicating that the water gas shift reaction occurs. A higher productivity and lower C2Hx products were observed at larger gas gaps. The highest overall energy efficiency achieved, including electrical power consumption, was 82% for all products or 66% for H2 only.

Plasma steam reforming of E85 for hydrogen rich gas production

E85 (85 vol% ethanol and 15 vol% gasoline) is a partly renewable fuel that is increasing in supply availability. Hydrogen production from E85 for fuel cell or internal combustion engine applications is a potential method for reducing CO2 emissions. Steam reforming of E85 using a nonthermal plasma (pulse corona discharge) reactor has been exploited at low temperature (200–300 °C) without external heating, diluent gas, oxidant or catalyst in this work. Several operational parameters, including the discharge current, E85 concentration and feed flow rate, have been investigated. The results show that hydrogen rich gases (63–67% H2 and 22–29% CO, with small amounts of CO2, C2 hydrocarbons and CH4) can be produced by this method. A comparison with ethanol reforming and gasoline reforming under identical conditions has also been made and the behaviour of E85 reforming is found to be close to that of ethanol reforming with slightly higher C2 hydrocarbons yields.

Remarkable improvement in the activity and stability of Pd/HZSM-5 catalyst for methane combustion

Abstract A novel Pd/HZSM-5 catalyst was prepared first by glow discharge plasma treatment followed by calcination thermally. Such prepared catalyst shows a higher activity and an enhanced stability for methane combustion. The XRD characterization and XPS analysis confirm that the plasma preparation leads to a better preparation of PdO active species over the HZSM-5 support. Especially, a plasma-enhanced acidity has been achieved upon the FT-IR analysis. The enhanced acidity plays an important role in stabilizing the dispersed PdO active species on the zeolite support.

A DFT study of CO 2 electrochemical reduction on Pb(211) and Sn(112)

Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfaces based on the results of density functional theory slab calculations. We mapped out the potential energy profiles for electrochemical reduction of CO2 to formate and other possible products on both surfaces. Our results show that the first step is the formation of the adsorbed formate (HCOO*) species through an Eley-Rideal mechanism. The formate species can be reduced to HCOO− through a one-electron reduction in basic solution, which produces formic acid as the predominant product. The respective potentials of forming HCOO* are predicted to be −0.72 and −0.58 V on Pb and Sn. Higher overpotentials make other reaction pathways accessible, leading to different products. On Sn(112), CO and CH4 can be generated at −0.65 V following formate formation. In contrast, the limiting potential to access alternative reaction channels on Pb(211) is −1.33 V, significantly higher than that of Sn.

Vapor‐Phase Hydrodeoxygenation of Guaiacol to Aromatics over Pt/HBeta: Identification of the Role of Acid Sites and Metal Sites on the Reaction Pathway

A comparative study of the hydrodeoxygenation of guaiacol, a phenolic compound derived from the lignin fraction of biomass with both hydroxyl and methoxyl functional groups, was performed on HBeta, Pt/SiO2, and Pt/HBeta at 350 °C and atmospheric pressure. The reaction pathway and the roles of the acid and metal sites were studied. Acid sites catalyze transalkylation and dehydroxylation reactions to produce monohydroxyl phenolics (phenol, cresols, and xylenols) as the major final products. Pt sites catalyze demethylation to result in catechol as the primary product, which can either be deoxygenated to phenol followed by phenol to benzene, or decarbonylated to cyclopentanone and further to butane. The close proximity of Pt and acid sites in bifunctional Pt/HBeta improves transalkylation and deoxygenation (or dehydroxylation) reactions and inhibits demethylation and decarbonylation reactions significantly, which leads to aromatics as the major final products with a total yield >85 %. Both the activity and stability of bifunctional Pt/HBeta during the hydrodeoxygenation of guaiacol are improved compared to those of HBeta and Pt/SiO2. The addition of water to the feed further improves the activity and stability through the hydrolysis of the O−CH3 bond of guaiacol on acid sites and the removal of coke around Pt.

Effect of Catalyst Preparation on Carbon Nanotube Growth

A highly dispersed Ni–Fe/Al2O3 catalyst was prepared by glow discharge plasma treatment followed by thermal calcinations. With this plasma prepared catalyst, carbon nanotubes encapsulated with metal particle or filled with nickel nano-wire were produced. This is very different from the conventional catalyst, with which the normal multi-wall carbon nanotubes or nano-capsule chains were synthesized. The plasma preparation leads to a significant change in the interaction between metal and the support.