Identifying the structure sensitivity of catalysts in reactions, such as Fischer−Tropsch synthesis from CO and H 2 over cobalt catalysts, is an important yet challenging issue in heterogeneous catalysis. Based on a first-principles kinetic study, we find for the first time that CO activation on hexagonal close-packed (HCP) Co not only has much higher intrinsic activity than that of face centered-cubic (FCC) Co but also prefers a different reaction route, i.e., direct dissociation with HCP Co but Hassisted dissociation on the FCC Co. The origin is identified from the formation of various denser yet favorable active sites on HCP Co not available for FCC Co, due to their distinct crystallographic structure and morphology. The great dependence of the activity on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity.I dentifying the structure sensitivity of catalysts in chemical reactions to achieve the maximum mass-specific yet stable reactivity is one of the most challenging goals in heterogeneous catalysis. 1 A growing number of studies are conducted to understand the nature of the structure sensitivity, supported by well-defined preparation methods, in situ characterizations, surface science studies, and ab initio calculations. A prime example of this complex structure sensitivity is the Fischer− Tropsch synthesis (FTS) converting CO and H 2 from coal, natural gas, and biomass to hydrocarbon over cobalt catalysts. 2 Over the years, two notable structure sensitivities have been observed for FTS over Co catalysts, i.e., crystallographic structure and particle size. First, it is noted that Co can exist in two crystallographic structures, namely, the hexagonal closepacked (HCP) phase and the face-centered cubic (FCC) phase, and both phases are found in FTS. It has been reported by many that HCP Co has higher FTS activity than FCC Co. 3 This structure sensitivity is, however, complicated by a phase transition from HCP to FCC upon decreasing the catalyst size, 4 varying the supports and promoters, and pretreating the catalysts. 5 To our best knowledge, it remains open as to whether and why HCP Co catalysts have higher FTS activity than FCC ones, which prevents the full exploration of this structure sensitivity. Second, there are a number of reports on the effect of particle size of Co catalysts on FTS activity; namely, the turnover frequency (TOF) was constant for crystallites above a certain diameter, but when the diameter became smaller, the TOF decreased. 6 It is unclear whether the decrease of FTS activity at the smaller particle size is related to the phase transition of the Co catalyst from HCP to FCC, because of the complexity of the FTS and the absence of sufficient crystallographic structure data. Nevertheless, it is clear that one cannot increase the mass-specific activity of Co catalysts in FTS simply by decreasing the particle size.We report here a density functional theory (DFT)-base...

Supercapacitors based on freestanding and flexible electrodes that can be fabricated with bacterial cellulose (BC), multiwalled carbon nanotubes (MWCNTs), and polyaniline (PANI) are reported. Due to the porous structure and electrolyte absorption properties of the BC paper, the flexible BC‐MWCNTs‐PANI hybrid electrode exhibits appreciable specific capacitance (656 F g−1 at a discharge current density of 1 A g−1) and remarkable cycling stability with capacitance degradation less than 0.5% after 1000 charge–discharge cycles at a current density of 10 A g−1. The facile and low‐cost of this binder‐free paper electrode may have great potential in development of flexible energy‐storage devices.

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