Co3O4‑Promoted CeriumOxide Catalyst for Efficient Catalytic N‑Alkylationof Amines with Alcohols

A series of CuO/CeO2 catalysts were prepared through a two-step process: (1) CeO2 supports were firstly prepared by precipitation (P), hydrothermal (HT) and sol-gel (SG) methods, respectively; and (2) CuO was deposited on the above CeO2 supports by deposition-precipitation method. The as-synthesized CeO2 supports and CuO/CeO2 catalysts were characterized by N2-physisorption, XRD, XPS, Raman, and H2-TPR. The CuO/CeO2 catalysts were examined with respect to their catalytic activity for the water–gas shift reaction, and their catalytic activities are ranked as: CuO/CeO2-P > CuO/CeO2-HT > CuO/CeO2-SG. The results suggest that the CeO2 prepared by precipitation (i.e., CeO2-P-300) has the best thermal stability and the most amounts of surface oxygen vacancies, which make the corresponding CuO/CeO2-P catalyst present the largest pore volume, the smallest crystal size of CuO, the highest microstrain (i.e., the highest surface energy) and the most amounts of active sites (i.e., the moderate copper oxide (crystalline) interacted with surface oxygen vacancies of ceria). Therefore, the catalytic activity of CuO/CeO2 catalysts, in nature, depends on the thermal stability and the number of surface oxygen vacancies of the CeO2 supports previously prepared by different methods.

Hydrothermal and co-precipitation methods were studied as two different methods for the synthesis of CeO2nanocatalysts. Co/CeO2 catalysts supported by 2, 4, 6, or 8wt% Co were further synthesized through impregnation and the performance of the catalytic oxidation of CO has been investigated. The highest specific surface area and the best catalytic performance was obtained by the catalyst 4wt% Co/CeO2 with the CeO2 support synthesized by the hydrothermal method (4% Co/CeO2-h), which yielded 100% CO conversion at 130 °C. The formation of CeO2 nanoparticles was confirmed by TEM analysis. XRD and SEM-EDX mapping analyses indicated that CoOx is highly dispersed on the 4% Co/CeO2-h catalyst surface. H2-TPR and O2-TPD results showed that 4% Co/CeO2-h possesses the best redox properties and the highest amount of chemically adsorbed oxygen on its surface among all tested catalysts. Raman and XPS spectra showed strong interactions between highly dispersed Co2+ active sites and exposed Ce3+ on the surface of the CeO2 support, resulting in the formation of the strong redox cycle Ce4+ + Co2+↔ Ce3+ + Co3+.This may explain that 4% Co/CeO2-h exhibited the best catalytic activity among all tested catalysts.

Insight into Single-Atom-Induced Unconventional Size Dependence over CeO2-Supported Pt Catalysts

A new and straightforward method for convenient synthesis of quinolines via a ruthenium‐catalyzed hydrogen‐transfer strategy has been demonstrated. By employing a commercially available ruthenium catalyst system, different α‐2‐nitroaryl alcohols were efficiently converted in combination with a variety of alcohols into various substituted products in reasonable to good yields upon isolation. The synthetic protocol is operationally simple with a broad substrate scope, and there is no need for the use of specialized reducing agents, making it a practical approach for versatile preparation of various quinoline derivatives.

Direct synthesis of quinazolinones via the carbon-supported acid-catalyzed cascade reaction of isatoic anhydrides with amides and aldehydes

A comparative study of CO oxidation over Cu-O-Ce solid solutions and CuO/CeO2 nanorods catalysts

Three morphology CeO2 supports with three-dimensionally ordered mesoporous structure (3DOM), nanotubes (NT) and nanocubes (NC) were synthesized by nanocasting of a mesoporous silica KIT-6 template with cubic Ia3d symmetries, hydrothermal method with and without urea, respectively, and supported cobalt catalysts were investigated on the production of COx-free hydrogen from ammonia decomposition for 300-600oC. Morphological structure of CeO2 significantly influenced the catalytic activities in the ammonia decomposition, and the Co/CeO2-3DOM catalyst had a higher catalytic performance than Co/CeO2-NC and Co/CeO2-NT. It was elucidated by the formation of smaller particles size and more oxygen vacancies. The Co/CeO2-3DOM catalyst exhibited good stability and reusability at 600oC for ammonia decomposition due to the three-dimensionally ordered mesoporous structure as anchoring cobalt active sites and prevention from active site aggregation. A mechanistic insight has been presented to understand the structure-activity relationship based on the structure of the CeO2 supports.

Increasing global concern over the rise of human emissions of CO2 into Earth’s atmosphere has prompted extensive research into ways of utilizing this gas for better economical use. The reaction of CO2 with methane to produce more valuable compounds is one of the important subjects in catalysis, energy and environmental research, since it provides a pathway to reduce these greenhouse gases. This thesis focuses on the development of novel metal-oxide catalysts for the production of synthesis gas (syngas ─ CO and H2) via CO2 reforming of methane, using both the conventional fixed-bed and microwave reactor systems. Mono- and bimetallic catalysts with good microwave absorption properties will be synthesized, and their performances investigated under both catalytic systems. This thesis aims to study the impact of a clean, strong, metal-support interaction on syngas production via CO2 reforming of methane, and to determine the best possible approach to generate carbonaceous materials in a way that is not detrimental to the performance of the catalysts during the reforming reaction. Synthesis of mono-metallic catalysts via hydrothermal method was conducted then treated using conventional thermal calcination and microwave plasma treatment. Microwave plasma’s power and exposure time effects on metal-support interface generation and catalytic performance in the reforming reaction were investigated. Increase in the plasma power from 150 to 250 W generated nanosized nickel particles of 1.5−4 nm on ceria support, whose particle sizes range between 30−85 nm. Conventional thermal calcination generated nickel particle size of 3−30 nm dispersed within the CeO2 support. The catalytic performances of both the plasma treated and the thermally calcined materials were then tested in CO2 with methane using the conventional fixed-bed reactor. The plasma treated samples showed superior and more stable turnover frequencies (TOFs) with time than the thermally calcined samples, which can be ascribed to the strong metal-support interaction and formation of well-dispersed Ni particles generated as a result of concurrent treatment of both the uncalcined ceria support and the loaded metal precursor. Synthesis of bi-metallic catalysts used for syngas production via CO2 reforming of methane using both conventional fixed-bed and microwave reactor systems was then examined. Three different bi-metallic catalysts were synthesized via hydrothermal approach and treated using the conventional thermal calcination. The promoters were chosen based on their potential to either enhance microwave absorption properties or suppress active metal (nickel particle) II enlargement during the synthesis and reaction stages. The performances of these bi-metallic catalysts were investigated in reforming reaction using the fixed-bed reactor to optimize the production of syngas. Our main aims in using the microwave reactor system for the reforming reaction are (i) tuning the formation of the carbonaceous materials via selective heating mechanism, since microwave radiation absorption solely depends on the catalyst properties, (ii) producing carbonaceous materials that will not hinder syngas production but might assist catalytic reaction, and (iii) utilizing the produced carbon composites in electrochemical applications, such as fuel cells. Carbon is well known for its poisoning effect on catalysts during syngas production using the conventional fixed-bed reactor, but its impact on catalytic performance might differ under microwave irradiation, since some carbonaceous materials have excellent microwave absorption properties. Different nanocarbons were grown in-situ on the bi-metallic catalysts by a selective heating mechanism, tuning their structures by the catalytic metal ions which controlled microwave absorption. Superior catalytic performance was obtained on the graphene-containing composite which is attributed to the locally-heated nickel particles. Morphology and composition also determine electrochemical performance, with the highest specific capacitance of ~60 F/g obtained on the multi-walled carbon nanotube/graphitic nanofiber composite. This work opens up excellent way to utilize carbonaceous materials, generally regarded as “waste”, as electrode materials for energy storage devices. It may also have other applications, such as for biosensors, adsorption and batteries.

Reinforcement of methanol catalytic reforming for hydrogen production through Ru-based carbon-coated CeO2 catalyst

Influence of preparation methods of supports on the deNOx performance and alkali-metal resistance over TiO2/CeO2 catalysts in NH3-SCR reaction

CO2 reforming of CH4 (CRM) is not only beneficial to environmental protection, but also valuable for industrial application. Different CeO2 supports were prepared to investigate the matching between Ni and CeO2 over Ni/CeO2 and its effect on CRM. The physicochemical properties of Ni/CeO2-C (commercial CeO2), Ni/CeO2-H (hydrothermal method) as well as Ni/CeO2-P (precipitation method) were characterized by XRD, N2 adsorption at − 196 °C, TEM, SEM–EDS, H2-TPR, NH3-TPD and XPS. Ni0 with good dispersion and CeO2 with more oxygen vacancies were obtained on Ni/CeO2-H, proving the influence on Ni/CeO2 catalysts caused by the preparation methods of CeO2. The initial conversion of both CO2 and CH4 of Ni/CeO2-H was more than five times that of Ni/CeO2-P and Ni/CeO2-C. The better matching between Ni and CeO2 on Ni/CeO2-H was the reason for its best catalytic performance in comparison with the Ni/CeO2-C and Ni/CeO2-P samples.

The controlled preparation and performance of Fe, Co-modified porous ceria nanorods for the total oxidation of propane

Surface-structure effect of nano-crystalline CeO2 support on low temperature CO oxidation

Deciphering the structural origin for the remarkable CO oxidation activities of the CuO-based catalysts with diverse morphological CeO2 supports

Enhanced low-temperature CO oxidation activity through crystal facet engineering of Pd/CeO2 catalysts