Characterization Of Catalysts Research Articles

NiCoMo nanoparticles as an efficient electrocatalyst for methanol electro‐oxidation in alkaline media

AbstractUsing the electrospinning approach, various percentages of less expensive metal alloy‐decorated nanofiber catalysts have been successfully made as a substitute for platinum in direct methanol fuel cells (DMFC). This work focuses on the synthesis and characterization of catalysts with metal fixed ratio of 20% wt for DMFC applications, specifically Ni/CNFs, Co/CNFs, and NiCoMo/CNFs. The catalysts are characterized using various techniques, including x‐ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive x‐ray, and electrochemical measurements. All the prepared samples, regardless of the metal concentration, had good nanofiber form and a distinct nanoparticle appearance, according to the scanning electron microscope (SEM). Chromatography, scan rate, response time, and cyclic voltammetry all were used to examine the samples' ability to perform methanol electrocatalysis. When Mo is added to Ni with Co, the electrooxidation reaction's activation energy and electrode stability both increase. With a starting potential of 0.22 V, the maximum current density in the NiCoMo/CNF sample was 99.8 mA/cm2 at 0.6 V. To electrooxidize methanol, our electrocatalysts combine diffusion control with kinetic‐limiting processes. This work has shown how to create an effective NiCoMo based methanol electrooxidation catalyst using a special technique.

Synthesis and Characterization of Carbon-Based Heterogeneous Catalysts for Energy Release of Molecular Solar Thermal Energy Storage Materials.

Molecular solar thermal energy storage (MOST) systems are rapidly becoming a feasible alternative to energy storage and net-zero carbon emission heating. MOST systems involve a single photoisomerization pair that incorporates light absorption, storage, and heat release processes in one recurring cycle. Despite significant recent advancements in the field, the catalytic back-reaction from MOST systems remains relatively unexplored. A wide range of applications is possible, contingent on the energy densities of the specific photoisomers. Here, we report platinum-, copper-, and nickel-based heterogeneous catalysts screened in batch conditions for the back-conversion reaction on the cyano-3-(4-methoxyphenyl)-norbornadiene/quadricyclane pair. Catalyst reactivities are investigated using structural characterization, imaging techniques, and spectroscopic analysis. Finally, the thermal stability is also explored for our best-performing catalysts.

Synthesis & Characterization of Novel CaO-based Heterogeneous Catalysts for Efficient Biodiesel Production from Waste Cooking Oil

Synthesis & Characterization of Novel CaO-based Heterogeneous Catalysts for Efficient Biodiesel Production from Waste Cooking Oil

Low-temperature methanation of fermentation gas with Ni-based catalysts in a multicomponent system

A large amount of greenhouse gases, such as carbon dioxide and methane, are released during the production process of bioethanol and biogas. Converting CO2 into methane is a promising way of capturing CO2 and generating high-value gas. At present, CO2 methanation technology is still in the early stage. It requires high temperature (300–400 ℃) and pressure (> 1 MPa), leading to high cost and energy consumption. In this study, a new catalyst, Ni–Fe/Al–Ti, was developed. Compared with the activity of the common Ni/Al2O3 catalyst, that of the new catalyst was increased by 1/3, and its activation temperature was reduced by 100℃. The selectivity of methane was increased to 99%. In the experiment using simulated fermentation gas, the catalyst showed good catalytic activity and durability at a low temperature and atmospheric pressure. Based on the characterization of catalysts and the study of reaction mechanisms, this article innovatively proposed a Ni–Fe/Al–Ti quaternary catalytic system. Catalytic process was realized through the synergism of Al–Ti composite support and Ni–Fe promotion. The oxygen vacancies on the surface of the composite carrier and the higher activity metals and alloys promoted by Fe accelerate the capture and reduction of CO2. Compared with the existing catalysts, the new Ni–Fe/Al–Ti catalyst can significantly improve the methanation efficiency and has great practical application potential.

Role of H2O in Catalytic Conversion of C1 Molecules.

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.

Ni modulates the coordination environment of cations in Fe3O4 to efficiently catalyze lignin depolymerization

Lignin shows great potential for sustainable production of high-quality fuels and value-added chemicals. The development of efficient and highly stable multifunctional catalysts for the depolymerization of lignin into aromatic chemicals remains a great challenge. In this work, environmentally friendly NiFe2O4 spinel catalyst characterizing with rich oxygen vacancies and porous structures was constructed by introducing Ni to modulate the coordination environment of cations in Fe3O4. Under optimal conditions, the conversion of alkali lignin catalyzed by NiFe2O4 reached 91.0%, the yield of liquid product reached 83.6% and the yield of aromatic monomer products was 31.7%. Combined results from catalyst characterization, product analysis and density functional theory calculations showed that the Lewis acidic center of the catalyst was significantly improved by the introduction of Ni, which promoted the C-O bond breaking in lignin. The Ni-O-Fe structure facilitated the adsorption of lignin substrates and reaction intermediates, which resulted in the improved depolymerization efficiency of lignin. The present work provides valuable insights into the depolymerization of lignin by spinel catalysts, and offers ideas for the future design and development of binary or even ternary spinel catalysts for the depolymerization of lignin.

Surficial engineering of active hydroxyls for ambient formaldehyde oxidation via enhanced Lewis acidity over Zr-doped cryptomelane materials

Lewis acids of solid catalysts have been featured for a pivotal role in promoting various reactions. Regarding the oxidation protocol to remove formaldehyde, the inherent drawback of the best-studied MnO2 materials in acidic sites has eventually caused deficiency of active hydroxyls to sustain low-temperature activity. Herein, the cryptomelane-type MnO2 was targeted and it was tuned via incorporation of Zr metal, exhibiting great advances in not only the complete HCHO-to-CO2 degradation but also cycling performance. Zr species were existent in doping state in the MnO2 lattice, rendering lower crystallinity and breaking the regular growth of MnO2 crystallites, which thereby tripled surface area and created larger volume of smaller mesopores. Meantime, the local electronic properties of Mn atoms were also changed by Zr doping, i.e., more low-valence Mn species were formed due to the electron transfer from Zr to Mn. The results of infrared studies demonstrate the higher possession of Lewis acid sites on ZrMn, and this high degree of electrophilic agents favored the production of hydroxyl species. Furthermore, the reactivity of surface hydroxyls, as investigated by CO temperature programmed reduction and temperature programmed desorption of adsorbed O2, was obviously improved as well after Zr modification. It is speculated jointly with the characterizations of the post-reaction catalysts that the accelerated production of active hydroxyls helped rapidly convert formaldehyde into key intermediate—formate, which was then degraded into CO2, avoiding the side reaction path with undesired intermediate—hydrocarbonate—over the pristine MnO2, where active sites were blocked and formaldehyde oxidation was inhibited. Additionally, Zr decoration could stabilize Lewis acidity to be more resistant to heat degeneration, and this merit brought about advantageous thermal recyclability for cycled application.

Electrocatalytic and Photocatalytic CO2 Methanation: From Reaction Fundamentals to Catalyst Developments

AbstractTransitioning from fossil fuels to renewable energy sources is demanded due to the gradual depletion of petroleum oil/gas and the environmental impact of carbon dioxide (CO2) emissions into the atmosphere. Electrocatalytic and photocatalytic CO2 reduction to methane (CH4) using renewable energy sources is crucial for sustainable chemical/fuel production and greenhouse gas reduction. In recent years, extensive research has focused on understanding the fundamental aspects of the two approaches, such as reaction mechanisms and active sites, and exploring/designing novel catalytic materials. This review initially discusses the reaction fundamentals, including performance evaluation indexes, reactors, and mechanisms, to understand the catalytic reactions. Subsequently, various catalyst preparation strategies and characterization methods are summarized, trying to outline the catalyst design principle based on the obtained understanding of the reaction mechanisms. Finally, research challenges and perspectives for future development in this area are discussed and presented. It is expected to provide a comprehensive understanding of the photo/electrocatalytic CO2 methanation, valuable knowledge to novice researchers, and a helpful reference for future research endeavors.

Synthesis and Characterization of Sorbitol Membraneless Alkaline Fuel Cell Catalysts for Cathode and Anode, Utilizing AgV2O5/C, AgMnO2/C, and PdCeO2/C Catalysts

This study aimed to develop sorbitol fuel cell catalysts for cathode and anode fuels by synthesizing AgV2O5/C, AgMnO2/C, and PdCeO2/C catalysts. The physical characteristics of the catalysts were analyzed using SEM and EDS. The results showed that the prepared catalysts were small, lumpy, and densely clustered on the carbon surface with small particles. The electrochemical characteristics of the oxidation of alkaline fuels using sorbitol as fuel were investigated by assessing sorbitol concentration ratios of 0.1, 0.2, 0.3, 0.4 and 0.5 per 0.1 M alkaline KOH solution through cyclic voltammetry. The PdCeO2/C catalyst at a concentration of 0.1 M sorbitol solution exhibits the highest potential difference at the potential range of -0.5 to 0.5 V, resulting in a maximum current density of 0.2 mA/cm2. The AgV2O5/C and AgMnO2/C catalysts were tested in the reduction reaction, and the concentration ratios of sorbitol solution per 0.1 M alkaline KOH solution varied from 0.1 to 0.5 M. The results demonstrated a decrease in activity in the catalyst reduction reaction as the sorbitol solution concentration increased, indicating a potential correlation with enhanced oxidation resistance. HIGHLIGHTS In order to achieve the highest efficiency and suitability in an electric cell, it is essential for the AgV2O5/C and AgMnO2/C catalysts to possess excellent resistance to cathode oxidation The AgV2O5/C and AgMnO2/C catalysts function as cathode-side catalysts involved in reduction reactions. Consequently, it is imperative for these catalysts to exhibit exceptional resistance to oxidation at the cathode At a concentration of 0.1 M KOH solution, the PdCeO2/C catalyst exhibited a maximum oxidation current density of 0.2 mA/cm² GRAPHICAL ABSTRACT

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

BackgroundDriven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. ResultsIn this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SignificanceThis analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Dual-function macroalgae biochar: Catalyst for hydrogen production and electrocatalyst

In the current study, Enteromorpha intestinalis, a green macroalgae, has been utilized as a substrate to synthesise a new environmentally friendly and cheap dual-functional (catalyst and electrocatalyst) material. The catalyst was used for efficient hydrogen production from alcoholises sodium borohydride and as an anode catalyst for direct methanol fuel cell applications. At the catalyst synthesis stage, orthogonal arrays of Taguchi is used to find the optimum levels of independent variables for the superior catalyst performance that bears the modest kinetics. The experiments performed in accordance with the L16(45) type orthogonal array. The samples treated at relatively moderate acid, impregnation temperature, impregnation time, burning temperature and burning time showed higher catalytic activities with Exp(5) presenting the optimal catalytic activity followed by Exp(1), Exp(15), Exp(8) and Exp(12), respectively. The experimental levels of coded variables (acid molarity, impregnation temperature and time, burning temperature and time) for Exp(5) were 3 M, 50 °C, 24 h, 500 °C and 2 h., respectively. These finding suggest that providing maximum levels of each of independent variable will not provide high catalytic activity. Taking into account the binary and ternary interactions is an efficient way to determine optimal level of each parameter with regards to maximum hydrogen production rate. The morphological and structural characterization of the optimal catalyst was finally carried out with SEM- EDS, XRD and FT-IR. CV and EIS measurements were taken to determine the electrocatalytic activity of final biochar. Experimental studies revealed that the utilization of E. intestinalis-based electrocatalyst as an anode catalyst for direct fuel cell applications is promising. By employing advanced Taguchi-based experimentation, this research establishes the optimum levels of independent variables, enhancing the catalyst's performance, and highlighting a novel approach to modest kinetics improvement.

Hierarchical ZSM-5 zeolite supported RuOx catalysts via organic mesoporous porogens for catalytic oxidation of vinyl chloride

Hierarchical ZSM-5 zeolites supported RuOx catalysts were prepared via the addition of various organic mesoporous porogens (namely starch, cellulose and sucrose) for catalytic oxidation of vinyl chloride (VC). The usage of mesoporous porogens during catalysts preparation was favorable for boosting the catalytic activity of the resultant catalysts, and 1%RuOx/HZ5-10%sucrose exhibited the optimum catalytic activity, impressive catalytic stability and long-term durability. The structure-activity dependence from catalysts characterizations revealed that the higher specific surface area, more abundant strong acid sites and surface adsorbed oxygen species were regarded as the critical parameters for the noticeable improvement of catalytic activity. Based on in situ infrared spectroscopy analysis, 1%RuOx/HZ5-10%sucrose exhibited higher adsorption capacity and more efficient conversion of VC molecules with fewer formation of organic intermediates because of its superior catalytic activity in comparison with the single 1%RuOx/HZ5. Additionally, enol and carboxylate species were demonstrated to be the key organic intermediates in catalytic VC oxidation.

Dehydrative decarbonylation of fatty acids into long-chain olefins over CoNx/NC catalysts

The development of highly efficient, low-cost supported catalysts is crucial for directly deoxygenating biomass fatty acids to long-chain olefins. However, additive-free olefin production, by dehydrative decarbonylation from fatty acids, is scarcely conducted owing to competing decarboxylation reactions. Herein, a green and cost-effective strategy is presented to improve the Co-catalyzed dehydrative decarbonylation of stearic acid, which produces a mixture of heptadecenes with yields of up to 41.3 % and a paraffin yield of 14.7 %. Experimental data, along with a detailed catalyst characterization, revealed that the surface CoNx species acted as the dominant active sites. Furthermore, the specific catalytic performance can be attributed to the dense defect sites, abundant vacancies, and mesoporous structures of the N-doped Carbon (NC) support. The as-prepared CoNx/NC catalysts were recovered and reused up to three times without significant deactivation. Additionally, we propose a possible reaction mechanism for fatty acid deoxygenation. This research makes a significant contribution toward advancing the performance of noble-metal-free deoxygenation catalysts for the production of unsaturated compounds in biomass conversions.

Preparation and NH3-SCR catalytic performance of CeTiOx catalysts with different pore structures

To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiOx, three-dimensionally ordered macroporous (3DOM) CeTiOx, three-dimensionally ordered mesoporous (3DOm) CeTiOx and disordered mesoporous (DM) CeTiOx were synthesized by the sol-gel method. The NH3-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx, and the 3DOM-m CeTiOx shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 °C at a GHSV of 60000 h−1. The characterization of catalysts by XRD, SEM, BET, NH3-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiOx. 3DOM-m CeTiOx has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH3-SCR reaction over the 3DOM-m CeTiOx mainly follows the L-H and E-R mechanisms.

Coprecipitation and hydrothermal synthesis of CaO from dolomite in the presence of Sapindus rarak extract for biodiesel production: catalysts characterization and optimization.

High-purity CaO cubic crystallites extracted from limestone exhibited excellent activity as base catalysts for waste cooking oil (WCO) conversion into biodiesel. Saponin from Sapindus rarak extract acted as a surfactant in CaO extraction and transformation into well-defined cubic microcrystallites. The application of saponin from Sapindus rarak extract as a surfactant for CaO production results in a high level of CaO purity and particle size reduction compared to directly calcined limestone (CaO-MgO). The catalytic activity was evaluated on CaO from hydrothermal and co-precipitation synthesis, MgO and CaO-MgO derived from limestone, giving hydrothermal CaO catalysts enhanced biodiesel yield. Optimization of transesterification conditions using Box Behnken Design response surface methodology achieved 92.40% biodiesel yield at 65 °C, 3 h reaction time and when using 5% of CaO catalysts.

Study of promoted Cu/ZnO and Cu/ZrO2 catalysts for dimethyl adipate hydrogenolysis

Two supports (ZnO, ZrO2) and four promoters (Al2O3, ZnO, CoOx, NiO) were investigated to design environmentally-friendly Cu-based hydrogenolysis catalysts. Both catalyst characterization and activity in dimethyl adipate hydrogenolysis were described....

Revisiting ion-pair interactions in phase transfer catalysis: from ionic compounds to real catalyst systems.

Ion-pairing is a fundamental phenomenon that significantly influences phase-transfer catalysis. In this study, we conduct a comprehensive investigation of ion-pair interactions, aiming to establish a comprehensive understanding of their nature and implications. The study begins with the examination of polar ionic compounds to define the concept of an ion-pair in the context of phase-transfer catalysis. Subsequently, a diverse range of ion-pair catalyst models were explored to gain insight into the factors governing their interactions. Finally, the focus shifts towards the characterisation of real phase-transfer catalysts, bridging the gap between theoretical models and practical applications. Through a combination of computational approaches and theoretical analysis, this work provides valuable insight into the nature of ion-pair interactions within phase-transfer catalysis fields.

Characterization, Application and Optimization of Low Cost Heterogeneous Catalyst in the Production of Biodiesel Using Waste Vegetable Frying Oil

Characterization, Application and Optimization of Low Cost Heterogeneous Catalyst in the Production of Biodiesel Using Waste Vegetable Frying Oil

A Comprehensive Experiment Based on Electrocatalytic Nitrate Reduction into Ammonia: Synthesis, Characterization, Performance Exploration, and Applicable Design of Copper-based Catalysts

A Comprehensive Experiment Based on Electrocatalytic Nitrate Reduction into Ammonia: Synthesis, Characterization, Performance Exploration, and Applicable Design of Copper-based Catalysts

Recent advances in the synthesis, characterization, and catalytic consequence of metal species confined within zeolite for hydrogen-related reactions

We summarize and discuss the progress in the synthesis and characterization of zeolite-encapsulated metal catalysts, and the consequences of encapsulation in terms of activity, selectivity, and stability for the hydrogen-related catalytic reactions.