Identification of the crystal plane effect of the Co derived from Co3O4 nanocrystals (NCs) on Fischer–Tropsch synthesis (FTS) is important for developing high-performance FTS solid catalysts. However, the achievement of this goal is hindered by the complexity of the FTS and the absence of sufficient crystallographic structure data. In this study, we report that the experimental FT performance of the Co catalysts depends on the exposed crystal facets of the Co3O4 NCs. The exposed Co3O4 NC {112} facets have the highest catalytic activity and the lowest methane selectivity (6.2%) in comparison to those of the {111} and {001} planes. The evolution of the crystal planes during the reduction was investigated further, and the preferred orientation relationship induced by the Co3O4 → Co transformation was {112} → {10–11}, {111} → {0001}, and {001} → {11–20}. CO temperature-programmed surface reaction experiments and density functional theory calculations further verified that the high FT performance of Co3O4{112} can be attributed to the specific surface topology of its active phase (i.e., Co{10–11}). Our findings clarify that the activity and selectivity of the FTS reaction can be enhanced by the selective exposure of a specific crystal plane from Co3O4 and could open an avenue for the rational design of high-performance FTS catalysts.

No abstract

Polymer/metal oxide composites are promising candidates for the treatment of water pollution. Adsorption selectivity as well as a large adsorption capacity are two key factors for treating wastewater containing multiple ions. Herein, a PPy/TiO(O) composite with a heterojunction structure was first discovered to have novel selectivity toward heavy metal ions. An interesting self-doping nature of TiO(O) together with SO for PPy was reported. This interesting structure contributed to an impressive selective adsorption capability with an ascending order of Zn > Pb ≫ Cu in a ternary ion system, where the adsorption for Cu could be almost suppressed. Through the designed adsorption experiments and characterization techniques including Fourier transform infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopy, a universal synergistic mechanism for PPy/TiO(O) composite was first proposed and confirmed. The doping and dedoping of metal oxide (dopant) from the polymer dictates the adsorption selectivity, where the selectivity is determined by the interaction between TiO and heavy metal ions. This work may provide some useful guidelines for designing adsorbents with selectivity toward specific heavy metal ions.

Precise control of selectivity in hydrogenation reactions is a long-standing challenge. Surface decoration of nanocatalysts with transition-metal oxide nanoparticles (NPs) is an effective strategy to tailor the catalytic selectivity but generally at the expense of activity due to the blocking of active sites. Here, we report that constructing single-site metal oxide modifiers (NiO, CoO x , or FeO x ) on supported Au NPs by atomic layer deposition (ALD) can regulate their catalytic selectivity for nitroaromatic hydrogenation. The coverage of single-site metal oxide can be precisely tuned by altering the number of ALD cycles. The Au/TiO2 decorated with five cycles of NiO (Ni: 0.32 wt %) in the style of a single site can efficiently change the product selectivity from azo to azoxy compounds without significantly blocking the surface active sites. The density functional theory calculations indicate that the azoxybenzene bonded to the single-site NiO-decorated Au(111) with a larger adsorption energy, which inhibits the overhydrogenation of azoxybenzene and results in high azoxybenzene selectivity. Our work has demonstrated a general and efficient way to regulate the reaction selectivity of metal nanocatalysts by anchoring single-site metal oxide promoters.

No abstract