Ru@hyperbranched Polymer for Hydrogenation of Levulinic Acid to Gamma-Valerolactone: The Role of the Catalyst Support

Hydrogenation of levulinic acid (LA) obtained from cellulose biomass is a promising path for production of γ-valerolactone (GVL)—a component of biofuel. In this work, we developed Ru nanoparticle containing nanocomposites based on hyperbranched pyridylphenylene polymer, serving as multiligand and stabilizing matrix. The functionalization of the nanocomposite with sulfuric acid significantly enhances the activity of the catalyst in the selective hydrogenation of LA to GVL and allows the reaction to proceed under mild reaction conditions (100 °C, 2 MPa of H2) in water and low catalyst loading (0.016 mol.%) with a quantitative yield of GVL and selectivity up to 100%. The catalysts were successfully reused four times without a significant loss of activity. A comprehensive physicochemical characterization of the catalysts allowed us to assess structure-property relationships and to uncover an important role of the polymeric support in the efficient GVL synthesis.

Phonolite Material as Catalyst Support for the Hydrotreatment of Gas Oil and Vegetable Oil Type Feedstocks

Phonolite material has shown to be promising catalyst support for the deoxygenation of triglycerides. In this work, we continue with our previous research by synthesising and testing three acid-treated phonolite-supported Co-Mo, Ni-Mo and Ni-W catalysts for the hydrotreating of atmospheric gas oil and co-processing with rapeseed oil at industrial operating conditions (350–370 °C, WHSV 1–2 h−1, 5.5 MPa) in the continuous regime for more than 270 h. The phonolite-supported catalysts showed hydrotreating activity comparable with commercial catalysts, together with a complete conversion of triglycerides into n-alkanes. During co-processing, the Ni-promoted catalyst showed strong stability, with similar activity previous to the rapeseed oil addition. Our results enable us to evaluate the suitability of phonolite as catalyst support for the development of plausible alternatives to conventional hydrotreating catalysts for the co-processing of middle distillates with vegetable oils.

Electrochemical Passivation Properties of Valve Transition Metal Carbides

Transition metal carbides have the potential to be employed as corrosion protective coating for a variety of applications such as e.g. steel based bipolar plates, porous transport layers or as catalyst support in polymer electrolyte membrane fuel cells and water electrolyzers. Yet, little is known of their fundamental, intrinsic corrosion and passivation properties. Herein, we conducted a detailed electrochemical passivation study of various valve transition metal carbides such as titanium carbide, tantalum carbide or tungsten carbide. Via flow cell measurements coupled to an inductively coupled plasma mass spectrometer, the in-situ transition metal dissolution was monitored, and the faradaic dissolution efficiency was calculated. Together with the determination of the grown oxide layer via X-ray photoelectron spectroscopy, a thorough evaluation of the passivation efficiency was conducted. Moreover, it was shown that a beneficial stabilization effect can be achieved through alloying of different carbides, which paves the way towards tailor-made coatings or catalyst support materials.

A Review on the Hydroisomerisasion of n-Parafins over Supported Metal Catalysts

Catalytic hydroisomerization of n-paraffin aims to produce branched paraffin isomers and suppress cracking reactions in the production of the low cloud point of biodiesel. The development of the type of metal and catalyst support, amount of metal loading, and reaction conditions are important to increase the catalyst activity. A high performace catalyst for hydroisomerization bears bifunctional characteristics with a high level of hydrogenation active sites and low acidity, maximizing the progress of hydroisomerization compared to the competitive cracking reaction. In addition, a catalyst support with smaller pore size can hinder large molecular structure isoparaffins to react on the acid site in the pore thus providing good selectivity for converting n-paraffin. Catalysts loaded with noble metals (Pt or Pd) showed significantly higher selectivity for hydroisomerization than non-noble transition metals such as Ni, Co, Mo and W. The reaction temperature and contact time are also important parameters in hydroisomerization of long chain paraffin, because long contact times and high temperatures tend to produce undesired byproducts of cracking. This review reports several examples of supported metal catalyst used in the hydroisomerization of long chain hydrocarbon n-paraffins under optimized reaction conditions, providing the best isomerization selectivity results with the lowest amount of byproducts. The role of various metals and their supports will be explained mainly for bifunctional catalysts.

Mass Transfer in Hierarchical Silica Monoliths Loaded With Pt in the Continuous-Flow Liquid-Phase Hydrogenation of p-Nitrophenol

Sol-gel-based silica monoliths with hierarchical mesopores/macropores are promising catalyst support and flow reactors. Here, we report the successful preparation of cylindrically shaped Pt-loaded silica monoliths (length: 2 cm, diameter: 0.5 cm) with a variable mean macropore width of 1, 6, 10, or 27 μm at a fixed mean mesopore width of 17 nm. The Pt-loaded monolithic catalysts were housed in a robust cladding made of borosilicate glass for use as a flow reactor. The monolithic reactors exhibit a permeability as high as 2 μm2 with a pressure drop below 9 bars over a flow rate range of 2–20 cm3 min−1 (solvent: water). The aqueous-phase hydrogenation of p-nitrophenol to p-aminophenol with NaBH4 as a reducing agent was used as a test reaction to study the influence of mass transfer on catalytic activity in continuous flow. No influence of flow rate on conversion at a fixed contact time of 2.6 s was observed for monolithic catalysts with mean macropore widths of 1, 10, or 27 µm. As opposed to earlier studies conducted at much lower flow velocities, this strongly indicates the absence of external mass-transfer limitations or stagnant layer formation in the macropores of the monolithic catalysts.

The Impacts of Surface Microchannels on the Transport Properties of Porous Fibrous Media Using Stochastic Pore Network Modeling

A stochastic pore network modeling method with tailored structures is proposed to investigate the impacts of surface microchannels on the transport properties of porous fibrous media. Firstly, we simplify the original pore network extracted from the 3D images. Secondly, a repeat sampling strategy is applied during the stochastic modeling of the porous structure at the macroscale while honoring the structural property of the original network. Thirdly, the microchannel is added as a spherical chain and replaces the overlapped elements of the original network. Finally, we verify our model via a comparison of the structure and flow properties. The results show that the microchannel increases the permeability of flow both in the directions parallel and vertical to the microchannel direction. The microchannel plays as the highway for the pass of reactants while the rest of the smaller pore size provides higher resistance for better catalyst support, and the propagation path in the network with microchannels is more even and predictable. This work indicates that our modeling framework is a promising methodology for the design optimization of cross-scale porous structures.

Single Co3O4 Nanocubes Electrocatalyzing the Oxygen Evolution Reaction: Nano-Impact Insights into Intrinsic Activity and Support Effects

Single-entity electrochemistry allows for assessing electrocatalytic activities of individual material entities such as nanoparticles (NPs). Thus, it becomes possible to consider intrinsic electrochemical properties of nanocatalysts when researching how activity relates to physical and structural material properties. Conversely, conventional electrochemical techniques provide a normalized sum current referring to a huge ensemble of NPs constituting, along with additives (e.g., binders), a complete catalyst-coated electrode. Accordingly, recording electrocatalytic responses of single NPs avoids interferences of ensemble effects and reduces the complexity of electrocatalytic processes, thus enabling detailed description and modelling. Herein, we present insights into the oxygen evolution catalysis at individual cubic Co3O4 NPs impacting microelectrodes of different support materials. Simulating diffusion at supported nanocubes, measured step current signals can be analyzed, providing edge lengths, corresponding size distributions, and interference-free turnover frequencies. The provided nano-impact investigation of (electro-)catalyst-support effects contradicts assumptions on a low number of highly active sites.