Bimetallic NiFe nanoparticles supported on carbon nanotubes (CNTs) were prepared and evaluated for catalytic hydrodeoxygenation (HDO) of guaiacol, which is a model ligninderived compound. Appropriate combination of Ni and Fe demonstrated high activity and significantly enhanced selectivity to cyclohexane and phenol, whereas monometallic Ni and Fe catalysts displayed poor activities or selectivities. The tunable selectivity of guaiacol HDO was found to be dependent on Ni/Fe atomic ratios. Cyclohexane and phenol are major products over the Ni5Fe1/CNT and Ni1Fe5/CNT catalysts, respectively. Characterization results confirmed that NiFe alloys were formed and elicited synergistic effects on the HDO performance. The selectivity-switchable performance of NiFe/CNT may be due to the synergism between Ni domains, where H2 could be easily activated, and Fe domains, which exhibited strong oxophilicity. Deactivation was observed over the monometallic catalyst which may be ascribed to the agglomeration of active nanoparticles. Metallic size effect on the HDO reaction was further investigated using monometallic Ni/CNT, Fe/CNT and bimetallic NiFe/CNT catalysts.

No abstract

Atomically dispersed metal catalysts often exhibit superior performance compared to that of nanoparticle catalysts in many catalysis processes. However, these so-called "singleatom" catalysts have a consistently low loading density on the support surface and easily aggregate at high temperatures, hindering their practical application. Herein, we demonstrate a facile surface engineering protocol using molecule−surface charge transfer adducts to fabricate highly stable noble metal catalysts with atomic dispersion, using a Pt/CeO 2 catalyst as an example. The key of this approach is the generation of an adequate amount of Ce 3+ defective sites on the porous CeO 2 surface through the adsorption of reductive ascorbic acid molecules and a subsequent surface charge transfer process. Subsequently, noble metal Pt atoms can be well-dispersedly anchored onto the generated Ce 3+ sites of porous CeO 2 nanorods with a loading density of up to 1.0 wt %. The as-prepared highly dispersed Pt/CeO 2 catalyst showed outstanding catalytic activity at near room temperature toward CO oxidation, with excellent stability over several days, which is far superior to the traditional impregnation-prepared catalysts, the activity (complete conversion at 90 °C) of which is severely decayed within a couple of hours. The proposed synthetic route is simple yet versatile and can therefore be potentially applied to fabricate other supported noble metal catalysts with atomic dispersion.