Nano confinement and catalytic conversion of energy molecules

Catalysis, as a key and enabling technology, plays an increasingly important role in fields ranging from energy, environment and agriculture to health care. Rational design and synthesis of highly efficient catalysts has become the ultimate goal of catalysis research. Thanks to the rapid development of nanoscience and nanotechnology, and in particular a theoretical understanding of the tuning of electronic structure in nanoscale systems, this element of design is becoming possible via precise control of nanoparticles’ composition, morphology, structure and electronic states. In the present paper, we will illustrate the results on the structural and electronic properties of catalytically active centers in the nano-confined systems, as well as their catalytic activities. Based upon the concept of “Nano-Confined Catalysis”, novel catalyst has been designed by embedding low-valent iron atoms within the lattice of silicon dioxide. The active single iron site could catalyze the direct and selective conversion of methane exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C−C coupling, further oligomerization and hence coke deposition. At 1090 °C, methane conversion reaches a maximum at 48.1% and ethylene selectivity 48.4%, while the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The surface-confined iron sites delivered stable performance, with no deactivation observed during a 60-h test. This technology would allow the removal of the energy-intensive process of syngas production from the conventional natural gas utilization technologies. In addition, we recently established the concept of nano-composite catalysts comprising of metal oxides and zeolites, which effectively separates the active sites for CO and H2 activation from those for C−C coupling. CO and H2 are activated over the partially reduced metal oxides forming intermediates, which are subsequently converted to products within the confined pores of zeolites. As such, surface polymerization, a long-standing problem in the conventional Fischer-Tropsch synthesis invented more than 90 years ago, could be circumvented. This novel process for syngas conversion could achieve a high selectivity of light olefins (80%), surpassing the limit of 58% for C2−C4 light hydrocarbons by the ASF distribution. Furthermore such a bifunctional composite catalyst delivers stable performance and no obvious deactivation was observed within a over 3000 h stability test. These achievements open up new avenues for the developments of clean technologies for the efficient utilization of carbon resources, such as natural gas, coal and biomass, and are recognized as the “milestone in the direct synthesis of light olefins”. Now, his team is collaborating with companies to explore industrial applications, starting from a pilot-scale study.