One-step dimethyl ether (DME) synthesis from CO2/H2 was investigated using physical mixtures of Hf-promoted CuZnO catalysts and FER. Methanol synthesis, the first step of DME production, was also studied using the same Cu-based catalysts. The catalysts were characterized by XRD with Rietveld refinement, XRF, specific area analysis, CO2-TPD, NH3-TPD, DRIFTS, N2O-RFC, and H2O dissociation measurements to evaluate oxygen vacancies. DFT calculations and thermodynamic analyses were also performed. Catalytic tests for methanol and DME synthesis under different reaction conditions, together with TG analysis, were conducted to investigate catalyst deactivation. Hf promotion significantly enhances catalytic performance by increasing both specific area and oxygen vacancy concentration through the substitution of Zn2+ by Hf4+ in the ZnO lattice. Consequently, methanol and DME yields increase up to an optimum Hf loading of 4 at.%, while the metallic Cu surface area remains essentially unchanged for Hf contents below 7 at.%. DFT calculations show that Hf substitution favors the spontaneous formation of oxygen vacancies in defective ZnO nanoparticles and on ZnO crystal surfaces. At higher Hf loadings, HfO2 formation blocks oxygen vacancies, active sites, and pores, leading to lower DME yield. Methanol synthesis reversibility under reaction conditions plays a decisive role in catalytic performance, favouring methanol and DME formation while suppressing CO. The proximity between methanol synthesis and dehydration sites enhances this effect. Furthermore, the acidity of the dehydration catalyst is an important factor controlling the DME formation rate. Catalyst deactivation is mainly attributed to H2O-promoted Cu sintering. Although CO is not an intermediate in methanol or DME synthesis, at high residence times CO produced by the reverse water-gas shift reaction can be re-adsorbed and hydrogenated to methanol and DME, allowing the system to approach thermodynamic equilibrium.
In this investigation, we have put forward a novel multi-criteria decision-making (MCDM) technique, intuitionistic fuzzy best–worst method (intuitionistic fuzzy BWM). Moreover, we have designed a novel hybrid MCDM technique called intuitionistic fuzzy best–worst analytic hierarchy process (intuitionistic fuzzy BWAHP) which is the amalgamation of intuitionistic fuzzy BWM and analytic hierarchy process (AHP). In this study, BWM finds its use to evaluate the weightage (or priority value) of criteria, and using AHP, the local weights of alternatives are decided. The proposed technique is utilized to recognize the most significant alternative (or indicator), for the efficiency of a water treatment plant. Observing the result, it can be said that the ‘water quality’ is the most responsible alternative. The consistency ratio value which is found by our proposed method is less, compared to the existing BWM and fuzzy BWM techniques. Finally, using a comparative study and sensitivity analysis, we verify the findings produced by our proposed method.
The performance of a solar photovoltaic (PV) panel boosted due to the reduction in cell temperature, which resulted an increase in the electrical performance. Hence, to enhance the performance of PV panels an experimental investigation was carried by incorporating 1-tetradeconal phase change materials (PCM), 40 % of biochar and 1 % of graphene. Four PV panels i.e., referenced PV panel, modified PV-PCM, modified PV with biochar PCM (PV-BPCM) and modified PV with nano enhanced biochar PCM (PV-NBPCM) were chosen for the experimental investigation to assess the thermal, electrical, economic and environmental analysis. It was found that the PVNBPCM exhibited better cooling effect with respect to the referenced PV panel, modified PV-PCM and modified PV-BPCM. The key findings from the comparative study suggested that the PV-NBPCM has reduced the maximum surface temperature around 18.86 K, compared to the other PV panels. While, the average electrical efficiency and power output of a PV-NBPCM was improved by 10.71 % and 24.60 %, respectively, against other proposed PV panels. The estimated levelized cost of electricity (LCOE), uniform end of annual cost (UEAC), and energy payback time (EPBT) for the PV-NBPCM was found to be lower compared to other PV configurations. Finally, the primary significance of using PCMs in solar panels is to improve their electrical efficiency and lifespan by managing the heat generated during operation.
BiLaCoGaO6 double perovskite ceramic system was prepared using a solid-state reaction method. Preliminary structural investigations were carried out by X-ray diffraction, which confirmed the existence of a monoclinic system at room temperature. The system holds considerable promise for microwave applications due to its increased dielectric constant as the applied frequency increases, confirming the validity of the dielectric HN model. The variation of the full-width-at-half-maximum (FWHM) curve of the electrical modulus indicates the presence of a non-Debye relaxation mechanism in the prepared sample. All the temperature data and the frequency dependence of the impedance were used to characterize the electrical conductivity of the sample, revealing a negative temperature coefficient resistance (NTCR). The Cole–Cole diagram shows that grains exhibit conductive behavior at lower frequencies. As the frequency approaches the characteristic frequency (f = 1/τ), a relaxation process occurs, resulting in a decrease in the dielectric constant. At very high frequencies (f > 1/τ), dipoles are unable to respond rapidly to the changing electric field, causing ε’ to approach a value close to ε’∞. BiLaCoGaO6 is a double perovskite ceramic whose unique structural and functional characteristics stimulated scientific interest. The crystal structure of this material is complicated, with layers of BiO6 and LaO12 polyhedral between corner-sharing octahedra of CoO6 and GaO6. Understanding the crystal structure of BiLaCoGaO6 and its physical characteristics is one of the main goals of this paper. Based on the electrical properties, the mixed ion-electronic conductivity of BiLaCoGaO6 makes it suitable for use in solid oxide fuel cells (SOFCs). Its strong temperature-dependent oxygen ion conductivity is very useful for efficient oxygen transfer in SOFC cathodes. To better understand the complex structure–property correlations of BiLaCoGaO6, this research aims to investigate the materials for their various electrical capabilities.
The non-Hermitian matrix-valued Brownian motion is the stochastic process of a random matrix whose entries are given by independent complex Brownian motions. The bi-orthogonality relation is imposed between the right and the left eigenvector processes, which allows for their scale transformations with an invariant eigenvalue process. The eigenvector-overlap process is a Hermitian matrix-valued process, each element of which is given by a product of an overlap of right eigenvectors and that of left eigenvectors. We derive a set of stochastic differential equations (SDEs) for the coupled system of the eigenvalue process and the eigenvector-overlap process and prove the scale-transformation invariance of the obtained SDE system. The Fuglede--Kadison (FK) determinant associated with the present matrix-valued process is regularized by introducing an auxiliary complex variable. This variable is necessary to give the stochastic partial differential equations (SPDEs) for the time-dependent random field defined by the regularized FK determinant and for its squared and logarithmic variations. Time-dependent point process of eigenvalues and its variation weighted by the diagonal elements of the eigenvector-overlap process are related to the derivatives of the logarithmic regularized FK-determinant random-field. We also discuss the PDEs obtained by averaging the SPDEs.
