Promotional effect of Co and Ni on MoO3 catalysts for hydrogenolysis of dibenzofuran to biphenyl under atmospheric hydrogen pressure

Solar-Driven Photothermal Catalytic Lignocellulosic Biomass-to-H2 Conversion

The conversion of lignocellulosic biomass to chemical fuel can achieve the sustainable use of lignocellulosic biomass, but it was limited by the lack of an effective conversion strategy. Here, we reported a unique approach of photothermal catalysis by using MoS2-reduced graphene oxide (MoS2/RGO) as the catalyst to convert lignocellulosic biomass into H2 fuel in alkaline solution. The RGO acting as a support for the growth of MoS2 results in the high exposed Mo edges, which act as efficient Lewis acidic sites for the oxygenolysis of lignocellulosic biomass dissolved in alkaline solution. The broad light absorption capacity and abundant Lewis acidic sites make MoS2/RGO to be efficient catalysts for photothermal catalytic H2 production from lignocellulosic biomass, and the H2 generation rate with respect to catalyst under 300 W Xe lamp irradiation in cellulose, rice straw, wheat straw, polar wood chip, bamboo, rice hull, and corncob aqueous solution achieve 223, 168, 230, 564, 390, 234, and 55 μmol·h-1·g-1, respectively. It is believed that this photothermal catalysis is a simple and "green" approach for the lignocellulosic biomass-to-H2 conversion, which would have great potential as a promising approach for solar energy-driven H2 production from lignocellulosic biomass.

Oxygen Healing and CO2 /H2 /Anisole Dissociation on Reduced Molybdenum Oxide Surfaces Studied by Density Functional Theory

Reduced molybdenum oxides are versatile catalysts for deoxygenation and hydrodeoxygenation reactions. In this work, we have performed spin-polarized DFT calculations to investigate oxygen healing energies on reduced molybdenum oxides (reduced α-MoO₃ , γ-Mo₄ O₁₁ and MoO₂ ). We find that Mo⁺⁴ on MoO₂ (100) is the most active for abstracting an oxygen from the oxygenated compounds. We further explored CO₂ adsorption and dissociation on reduced α-MoO₃ (010) and MoO₂ (100). In comparison to reduced α-MoO₃ (010), CO₂ adsorbs more strongly on MoO₂ (100). We find that CO₂ dissociates on MoO₂ (100) via a two-step process, the overall barrier for which is 0.6 eV. This barrier is 1.7 eV lower than that on reduced α-MoO₃ (010), suggesting a much higher activity for deoxygenation of CO₂ to CO. As H₂ dissociation is shown to be the rate-limiting step for hydrodeoxygenation reactions, we also studied activation barriers for H₂ chemisorption on MoO₂ (100). We find that the chemisorption barriers are 0.7 eV lower than that reported on reduced α-MoO₃ (010). Finally, we have studied the dissociation (C-O cleavage) of anisole (a lignin-based biofuel model compound) on MoO₂ (100). We find that anisole binds very strongly on MoO₂ (100) with an adsorption energy of -1.47 eV. According to Sabatier's principle, strongly adsorbing reactants poison the catalyst surface, which may explain the low activity of MoO₂ observed during experiments for hydrodeoxygenation of anisole.

Assessment of Lewis-Acidic Surface Sites Using Tetrahydrofuran as a Suitable and Smart Probe Molecule

Measuring the Lewis-acidic surface sites in catalysis is problematic when the material's surface area is very low (SBET ≤1 m2  ⋅ g-1 ). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO3 as pure and mixed with 5-30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pKb =16.08, rather than strong basic molecules such as NH3 (pKb =4.75) or pyridine (pKb =8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis-cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175-300 °C. A good agreement between the obtained data of sample MoO3 -10 % CdO, which is characterised by the highest surface area value, the population of Lewis-acidic sites and % selectivity of propylene at all the applied reaction temperatures was found.