Enhong Cao

Solvent-free aerobic oxidation of alcohols using supported gold palladium nanoalloys prepared by a modified impregnation method

The synthesis of stable, supported, bimetallic nanoalloys with controlled size, morphology and composition is of great practical importance. Compared to their monometallic analogues, such materials exhibit remarkable enhancement in functional properties, which can be exploited in various fields including catalysis. Recently, we have reported a simple excess anion modification of the impregnation method to prepare supported gold–palladium catalysts which gives very good control over the particle sizes and the composition without using any stabilizer ligands in the preparation. Here, we report the results from a comparative study of using this modified impregnation catalyst for the solvent-free aerobic oxidation of alcohols in two different reactors: a glass stirred reactor and a micro packed bed reactor under batch and continuous mode respectively. These modified impregnation catalysts are exceptionally active and more importantly, when tested in a micro packed bed reactor under flow conditions, are observed to be stable for several days without any sign of deactivation in contrast to the same catalyst prepared by the sol immobilization method in the presence of stabilizer ligands which showed a 3–5% decrease in conversion over 10–12 h.

A joint model-based experimental design approach for the identification of kinetic models in continuous flow laboratory reactors

Continuous flow laboratory reactors are typically used for the development of kinetic models for catalytic reactions. Sequential model-based design of experiments (MBDoE) procedures have been proposed in literature where experiments are optimally designed for discriminating amongst candidate models or for improving the estimation of kinetic parameters. However, the effectiveness of these procedures is strongly affected by the initial model uncertainty, leading to suboptimal design solutions and higher number of experiments to be executed. A joint model-based design of experiments (j-MBDoE) technique, based on multi-objective optimization, is proposed in this paper for the simultaneous solution of the dual problem of discriminating among competitive kinetic models and improving the estimation of the model parameters. The effectiveness of the proposed design methodology is tested and discussed through a simulated case study for the identification of kinetic models of methanol oxidation over silver catalyst.

Oxidation of cinnamyl alcohol using bimetallic Au–Pd/TiO2 catalysts: a deactivation study in a continuous flow packed bed microreactor

The stability of a bimetallic Au–Pd/TiO2 catalyst was examined in a packed bed microreactor for the oxidation of cinnamyl alcohol dissolved in toluene. The catalyst was prepared by co-impregnation with a Au–Pd weight ratio of 1 : 19. Experiments were performed at 80–120 °C, oxygen concentration 0–100% and total pressure 4 bara. Principal products observed were cinnamaldehyde, 3-phenyl-1-propanol and trans-β-methylstyrene. Although the same catalyst was shown to possess good stability in the oxidation of benzyl alcohol, it deactivated during the oxidation of cinnamyl alcohol, particularly at elevated reaction temperatures. Higher concentration of oxygen used for the reaction led to improved cinnamaldehyde selectivity but lower conversion and higher deactivation rates. Treatment with hydrogen recovered only a fraction of the activity. Deactivation was attributed to Pd leaching and a complex effect of oxygen.

A microwave promoted continuous flow approach to self-assembled hierarchical hematite superstructures

In this work, a microwave promoted flow (MWPF) system to reproducibly synthesize self-assembled hierarchical hematite superstructures (Hem-SSs) using the sole precursor (Fe(NO3)3·9H2O) and single mode microwave under aqueous conditions was developed. The functional characterisation by XRD, (HR)TEM, XPS, UV-vis and Raman spectroscopy proved that highly crystalline ellipsoid Hem-SSs (∼180 nm × 140 nm) were produced, built from primary hematite nanoparticles, 5–10 nm in size using 0.05 mol L−1 precursor concentration, 1 mL min−1 flow rate and short reaction time (about 6 min). Particles produced via conventional heating (CH) at 120 and 140 °C in the same flow reactor under similar experimental conditions were found to consist of mixtures of goethite and hematite. The effects of precursor concentration (0.1 and 0.2 mol L−1) and flow rate (2 and 5 mL min−1) were further investigated and the synthesis mechanism was also discussed. This novel method opens a window for continuous fabrication of metal or metal oxide nanoparticles/superstructures by a green approach.

Merging information from batch and continuous flow experiments for the identification of kinetic models of benzyl alcohol oxidation over Au-Pd catalyst

Despite the great industrial importance of benzaldehyde as a reaction intermediate, only a few attempts have been made in the literature to develop kinetic models able of characterising the catalytic oxidation of benzyl alcohol to benzaldehyde quantitatively both in batch and flow systems. The purpose of this paper is to merge the information obtained from a laboratory scale batch glass stirred reactor (GSR) with the information obtained from a continuous-flow micro-packed bed reactor (MPBR) for an accurate and quantitative description of the products distribution in these reaction systems. A two-stage procedure is applied for this purpose where experimental design techniques are used for evaluating the most promising regions of the experimental space for the identification of kinetic models.

Model-based design of experiments for the identification of kinetic models in microreactor platforms

Microreactor platforms represent advanced tools in reaction engineering for the quick development of reliable kinetic models. Experiments can be performed with a better reaction temperature control, enhanced heat and mass transfer and mixing of reactants. However, the effectiveness of the model identification procedure is strictly related to the execution of properly designed experiments, allowing elucidation of the reaction mechanisms and providing a precise estimation of the kinetic parameters. In this paper a model-based design of experiments (MBDoE) approach is proposed where experiments are designed for both discriminating among competing models and for improving the estimation of kinetic parameters. The procedure is tested on a real case study related to the identification of kinetic models of methanol oxidation on silver catalyst.