Vapor–Liquid Equilibrium of α‑Pinene, Longifolene, and Abietic Acid of Pine Oleoresin: HS-GC Measurements and Model Correlation

Investigating phase equilibrium on the terpenoid of the pine oleoresin system is of great importance for the usage relevant to the oleoresin. Herein, the binary and ternary isothermal vapor–liquid equilibrium (VLE) of α-pinene, longifolene, and abietic acid (three main components of oleoresin) at 313.15, 323.15, and 333.15 K were measured by headspace gas chromatography (HS-GC). There was no azeotropic behavior observed of α-pinene and longifolene. Abietic acid’s influence on separating α-pinene and longifolene was discussed. The relative volatilities of α-pinene and longifolene decrease in the presence of abietic acid, indicating a negative impact of abietic acid on their separation. The experimental data were correlated well with the nonrandom two-liquid, universal quasichemical, and Wilson models. The binary interaction parameters for each equation were also obtained, and the largest mean relative deviation of vapor-phase mole fraction and the largest absolute average deviation of pressure are 0.1975% and 0.0856 kPa, respectively

Microwave-Assisted Synthesis of Cu@IrO₂ Core-Shell Nanowires for Low-Temperature Methane Conversion

A facile microwave-assisted synthesis was developed for the tunable fabrication of a Cu@IrO2 core@shell nanowire motif. Experimental parameters, such as (i) the reaction time, (ii) the method of addition of the Ir precursor, (iii) the capping agent, (iv) the reducing agent, and (v) the capping agent-to-reducing agent ratio, were subsequently optimized. The viability of other methods based on the previously reported literature, such as refluxing, stirring, and physical sonication, was studied and compared with our optimized microwave-assisted protocol in creating our as-prepared materials. It should be noted that the magnitude of the IrO2 shell could be tailored based on varying the Cu:Ir ratio coupled with judicious variations in the amounts of the capping agent and the reducing agent. Structural characterization techniques, such as XRD, XPS, and HRTEM (including HRTEM-EDS), were used to analyze our Cu@IrO2 motifs. Specifically, the shell could be reliably tailored from sizes of 10, 8, 6, and 3.5 nm with corresponding Cu:Ir ratios of 10:1, 15:1, 20:1, and 25:1, respectively. Moreover, the structural integrity of the motifs was probed and found to have been maintained after not only heat treatment but also the post-methane conversion process, indicative of an intrinsically high stability. Both components within the CuO-IrO2 interface were able to activate methane at temperatures between 400 and 500 K with a reduction of the associated metal cations (Cu2+ → Cu1+; Ir4+ → Ir3+) and the deposition of CHx fragments on the surface, as clearly observed in the ambient-pressure XPS results. Thus, on the basis of their stability and chemical activity, these core-shell materials could be very useful for the catalytic conversion of methane into “higher-value” chemicals

Structural and Chemical Evolution of an Inverse CeO_<i>x</i>/Cu Catalyst under CO₂ Hydrogenation: Tunning Oxide Morphology to Improve Activity and Selectivity

Small nanoparticles of ceria deposited on a powder of CuO display a very high selectivity for the production of methanol via CO2 hydrogenation. CeO2/CuO catalysts with ceria loadings of 5%, 20%, and 50% were investigated. Among these, the system with 5% CeOx showed the best catalytic performance at temperatures between 200 and 350 °C. The evolution of this system under reaction conditions was studied using a combination of environmental transmission electron microscopy (E-TEM), in situ X-ray absorption spectroscopy (XAS), and time-resolved X-ray diffraction (TR-XRD). For 5% CeOx/Cu, the in situ studies pointed to a full conversion of CuO into metallic copper, with a complete transformation of Ce4+ into Ce3+. Images from E-TEM showed drastic changes in the morphology of the catalyst when it was exposed to H2, CO2, and CO2/H2 mixtures. Under a CO2/H2 feed, there was a redispersion of the ceria particles that was detected by E-TEM and in situ TR-XRD. These morphological changes were made possible by the inverse oxide/metal configuration and facilitate the binding and selective conversion of CO2 to methanol

Atomic Structural Origin of the High Methanol Selectivity over In₂O₃–Metal Interfaces: Metal–Support Interactions and the Formation of a InO_<i>x</i> Overlayer in Ru/In₂O₃ Catalysts during CO₂ Hydrogenation

CO2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al2O3 catalyst, an indium oxide (In2O3)-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In2O3, M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In2O3 despite the distinct chemical properties of the added metals. To investigate the phenomena behind this behavior, here we used RuO2/In2O3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO2/In2O3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO2 hydrogenation conditions, Ru clusters facilitate the reduction of In2O3 to generate In2O3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru0 sites for CH4 production are blocked while creating RuOx–In2O3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO2. This work reveals the dynamic nature of In2O3-based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol