Immobilized Ru Clusters in Nanosized Mesoporous Zirconium Silica for the Aqueous Hydrogenation of Furan Derivatives at Room Temperature

Abstract

Noble-metal clusters are important catalysts because of their unique structures and activities, which are associated with their metalÀmetal bonds.[1] Numerous methods have been developed to encapsulate metal clusters within porous materials or polymers to protect the clusters against sintering.[2] A common porous support is zeolite, owing to its intrinsic subnanometer pore diameters, which are similar to the size of the metal clusters and can confine and prevent the clusters from growing into big particles. This confinement allows metal clusters to activate reactants with small molecular sizes that are accessible to the pores. [3] Mesoporous silica provides an ideal support, owing to its large pore diameters, which are suitable for large-sized organic substrates and biomass derivatives.[4] Ligand-stabilized metal precursors are usually used to anchor the clusters within the mesoporous channel with a low loading of the metal.[5] Uniform mesoporous-silica-supported noble-metal clusters cannot be achieved by impregnation of the support in an aqueous solution of the metal salts because the pore diameter of mesoporous silica (> 2 nm) is larger than the size of the metal clusters. The metal clusters are easily grown into big particles with a broad size distribution.[6] The incorporation of heteroelements (Zr, Ti, Al, etc.) into mesoporous silica has been developed to disperse metal species.[7] However, some metal particles still migrate towards the outside of the support during the reduction step with hydrogen, which causes their aggregation into big particles and, hence, the blocking of the entrance to the pore channels. Therefore, substantial challenges remain towards the goal of synthesizing uniform metal clusters that are immobilized within mesoporous silica from the corresponding metal salts.Biomass becomes an increasingly important feedstock to produce fuels and chemicals for a sustainable future.[8] Furan derivatives have been identified as the key building blocks to synthesize valuable chemicals.[9] Besides its nontoxic and nonflammable properties, water is a desirable solvent because the furan derivatives are soluble under aqueous conditions.[10] Several catalysts have been developed for the hydrogenation of furan derivatives in water, but high reaction temperatures or high hydrogen pressures are required to achieve high activities because of the low aqueous solubility of hydrogen. [11] Herein, immobilized ruthenium clusters (50 Ru atoms) in nanosized mesoporous zirconium silica (MSN-Zr) were synthesized by using an impregnation method, starting from an aqueous solution of RuCl 3 . The Ru cluster catalyst showed remarkable activity for hydrogenation of furan derivatives in water at room temperature under 5 bar hydrogen pressure.MSN-Zr-x, which has a uniform hexagonal pore structure, was synthesized by modification of our previously reported two-step procedure, [12] in which x denotes the Si/Zr molar ratio (for the detailed preparation, see the Supporting Information). The morphology and pore structure are sim...

Investigation of the Hydrogenation of 5‐Methylfurfural by Noble Metal Nanoparticles in a Microcapillary Reactor

“…Using Ru, the expected selective hydrogenation of 1 yields the methylfurfuryl alcohol 2 as the main product, conversion by means of Pd nanoparticles resultsi nt he totally hydrogenated compound 4.A dditionally the presentedt hree-dimensional mass trace in Figure 2b shows that the high activity of the Ru catalysts ystem results in formation of the dehydrated and decarbonylated compounds 5, 6,a nd 8.I nc ase of the Pd catalystt his reactioni s negligible (Figure 2c). The same behavior was observed by other catalytic studies of furfural [8,11] and methylfurfural [5,10] and leads us to the assumption that in general the interaction of Pd with the aromatic furan ring is preferred. Recently,H ermans et al focusedo nt he catalytic conversion of furfural derivatives under continuous flow conditions in as tainlesss teel tubular reactor packed with aP dc atalyst.…”

“…This is in very good agreement with ac omparables tudy about Cu, Ni, and Pd catalysts by Resasco et al, [8] as well as the other reports regardingP da ss uitable catalyst for the total hydrogenation of furfural derivatives. [5,8,10,11] Whereas forR u the change in the catalyst loading reveals am ajor impact, in case of Pd we observed only as light increase in the total conversion (Figure 4). In summary,w ed emonstrated the applicability of our highthroughput experimentation setup using ocRGC for reaction systemsw ith increased complexity.O ur results show excellent agreement with various studies concerning the conversion of furfural derivatives over supported metal catalysts.…”

Selective liquid phase hydrogenation of furfural to furfuryl alcohol by Ru/Zr-MOFs

“…Ru/UiO-66 showed the highest activity with a furfural conversion of 94.9% and a TOF of 11 h −1 . The catalytic performance is close to that of Ru nanoparticles embedded in nanosized mesoporous Zrpromoted silica [26]. The activity of Ru/UiO-67 was nearly similar (11 h −1 ), despite the much lower surface area of this sample compared with UiO-66.…”

“…An inherent problem associated with water as solvent is that high reaction temperatures and high H 2 pressure are needed to achieve appreciable activity because of the low solubility of hydrogen in water [25]. Very recently, Chen et al succeeded in hydrogenating furfural by Ru clusters confined in nano-sized mesoporous zirconium-silica in water at room temperature [26]. This result constitutes a new approach for the production of furfuryl alcohol by using supported Ru nanoparticles.…”

Selective hydrodeoxygenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran on Ru–MoOx/C catalysts

“…The loss of reactivity of catalyst was probably attributed to deposit of carbonaceous species like humins, which formatted during the reaction and immersed in the active sites, as notied in previous reports. 26,56,57 To get insights into the deactivation of catalyst, the fresh and used catalysts were characterized by SEM, TEM and BET as follows. The result of SEM was presented at Fig.…”