Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbO(x)-based catalysts in the hydrodeoxygenation of furan-derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90% throughout) in a 256 h time-on-stream test. Experimental and theoretical studies showed that NbO(x) species play the key role in C-O bond cleavage. As a multifunctional catalyst, Pd/NbOPO4 plays three roles in the conversion of aldol adducts into alkanes: 1) The noble metal (in this case Pd) is the active center for hydrogenation; 2) NbO(x) species help to cleave the C-O bond, especially of the tetrahydrofuran ring; and 3) a niobium-based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan-derived adducts into alkanes under mild conditions.

The search for more efficient heterogeneous catalysts remains critical to the chemical industry. The Sabatier principle of maximizing catalytic activity by optimizing the adsorption energy of the substrate molecule could offer pivotal guidance to otherwise random screenings. Here we show that the chemical shift value of an adsorbate (formic acid) on metal colloid catalysts measured by (13)C nuclear magnetic resonance (NMR) spectroscopy in aqueous suspension constitutes a simple experimental descriptor for adsorption strength. Avoiding direct contact between the (13)C atom and the metal surface eliminates peak broadening that has confounded prior efforts to establish such correlations. The data can guide rational design of improved catalysts, as demonstrated here for the cases of formic acid decomposition and formic acid electro-oxidation reactions.

No abstract

Hydrogen adsorption and reaction on the rutile TiO 2 (011)-2×1 has been investigated by a combination of high-resolution scanning tunneling microscopy and density functional theory calculations. Hydroxyl formation on the reconstructed surface is weak, and hydroxyls have only been observed on one of the three different surface oxygen sites. Recombination of hydrogen and desorption of H 2 is prevented by a large kinetic barrier. Instead, hydrogen is removed from the surface at elevated temperature by diffusion into the bulk. This is contrasted with photoinduced processes investigated by UV−irradiation under ultra high vacuum conditions, which leads to desorption of hydrogen from the surface, indicating a photoinduced lowering of the reaction barrier. Our studies are also compared to previous studies on the rutile TiO 2 (110) surface where different thermal and photoinduced processes have been reported. These differences are explained by three competing reaction pathways: (i) bulk diffusion, (ii) H 2 recombination, and (iii) water formation at the surface by lattice oxygen abstraction. The dependence of the reaction on the hydrogen-adsorption energies as well as on kinetic diffusion and reaction barriers and pathways can explain the observed differences between these two surface orientations.

Figure 5. Calculated structures (a, b: two side views) of H 2 O molecules at the anatase TiO 2 (105) surface. H white, O dark gray, Ti gray.

Metal oxide surfaces have been thought to be fairly rigid. On the example of rutile TiO2(011) we show that this is not necessarily the case. This surface restructures by interacting with molecules. The synergic effect of adsorbates causes a strictly directional reorganization of the substrate, which results in one-dimensional adsorbate cluster formation. The increase in the surface energy of the restructured surface is compensated for by the larger molecular adsorption energy. The reversible change of the surface structure suggests a dynamic surface that may change its properties in response to adsorbed molecules.

No abstract

Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbOx‐based catalysts in the hydrodeoxygenation of furan‐derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90 % throughout) in a 256 h time‐on‐stream test. Experimental and theoretical studies showed that NbOx species play the key role in CO bond cleavage. As a multifunctional catalyst, Pd/NbOPO4 plays three roles in the conversion of aldol adducts into alkanes: 1) The noble metal (in this case Pd) is the active center for hydrogenation; 2) NbOx species help to cleave the CO bond, especially of the tetrahydrofuran ring; and 3) a niobium‐based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan‐derived adducts into alkanes under mild conditions.