CO2 Hydrogenation to Methanol over Ce and Zr Containing UiO-66 and Cu/UiO-66

Direct hydrogenation of CO2 to methanol is an interesting method to recycle CO2 emitted e.g., during combustion of fossil fuels. However, it is a challenging process because both the selectivity to methanol and its production are low. The metal-organic frameworks are relatively new class of materials with a potential to be used as catalysts or catalysts supports, also in the reaction of MeOH production. Among many interesting structures, the UiO-66 draws significant attention owing to its chemical and thermal stability, developed surface area, and the possibility of tuning its properties e.g., by exchanging the zirconium in the nodes to other metal cations. In this work we discuss—for the first time—the performance of Cu supported on UiO-66(Ce/Zr) in CO2 hydrogenation to MeOH. We show the impact of the composition of UiO-66-based catalysts, and the character of Cu-Zr and Cu-Ce interactions on MeOH production and MeOH selectivity during test carried out for 25 h at T = 200 °C and p = 1.8 MPa. Significant increase of selectivity to MeOH was noticed after exchanging half of Zr4+ cations with Ce4+; however, no change in MeOH production occurred. It was found that the Cu-Ce coexistence in the UiO-66-based catalytic system reduced the selectivity to MeOH when compared to Cu/UiO-66(Zr), which was ascribed to lower concentration of Cu0 active sites in Cu/UiO-66(Ce/Zr), and this was caused by oxygen spill-over between Cu0 and Ce4+, and thus, the oxidation of the former. The impact of reaction conditions on the structure stability of tested catalyst was also determined.This work was financed by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wrocław University of Technology and the project 0402/0100/17

The Impact of Synthesis Method on the Properties and CO2 Sorption Capacity of UiO-66(Ce)

A series of cerium-based UiO-66 was obtained via hydrothermal and sonochemical methods, using the same quantities of reagents (cerium ammonium nitrate (CAN), terephthalic acid (H2BDC)) and solvents) in each synthesis. The impact of synthesis method and metal to linker ratio on the structural and textural properties of obtained UiO-66(Ce), as well as their composition in terms of Ce4+/Ce3+ ratio, structure defects resulting from missing linker, and CO2 adsorption capacity was discussed. By using typical characterization techniques and methods, such as XRD, N2 and CO2 sorption, TGA, XPS, and SEM, it was shown that the agitation of reacting mixture during synthesis (caused by stirring or ultrasounds) allows to obtain structures that have more developed surfaces and fewer linker defects than when MOF was obtained in static conditions. The specific surface area was found to be of minor importance in the context of CO2 adsorption than the contribution of Ce3+ ions that were associated with the concentration of linker defects.This work was financed by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wrocław University of Technology and Project No 0402/0100/17

Opportunities and challenges in sustainable treatment and resource reuse of sewage sludge: A review

Sludge or waste activated sludge (WAS) generated from wastewater treatment plants may be considered a nuisance. It is a key source for secondary environmental contamination on account of the presence of diverse pollutants (polycyclic aromatic hydrocarbons, dioxins, furans, heavy metals, etc.). Innovative and cost-effective sludge treatment pathways are a prerequisite for the safe and environment-friendly disposal of WAS. This article delivers an assessment of the leading disposal (volume reduction) and energy recovery routes such as anaerobic digestion, incineration, pyrolysis, gasification and enhanced digestion using microbial fuel cell along with their comparative evaluation, to measure their suitability for different sludge compositions and resources availability. Furthermore, the authors shed light on the bio-refinery and resource recovery approaches to extract value added products and nutrients from WAS, and control options for metal elements and micro-pollutants in sewage sludge. Recovery of enzymes, bio-plastics, bio-pesticides, proteins and phosphorus are discussed as a means to visualize sludge as a potential opportunity instead of a nuisance

CNT and H2 Production During CH4 Decomposition over Ni/CeZrO2. I. A Mechanistic Study

This work presents a new insight into the potential of a Ni/CeZrO2 catalyst in two separate processes: (i) Chemical Vapor Deposition (CVD) using methane as a feedstock to obtain carbon nanotubes (CNTs) and H2, and (ii) catalyst regeneration with H2O that yields H2. The direct reaction of methane with H2O (steam methane reforming (SMR)) leads to H2 and CO (and CO2), whereas carbon deposition—regardless of its type—is an unwanted reaction. The concept presented in this work assumes dividing that process into two reactors, which allows one to obtain two valuable products, i.e., CNTs and H2. The literature data on CNT production via CVD ignores the issue of H2 formation. Moreover, there is no data concerning CNT production in fluidized bed reactors over ceria-zirconia supported metal catalysts. The results presented in this work show that CNTs can be formed on Ni/CeZrO2 during CH4 decomposition, and that the catalyst can be easily regenerated with H2O, which is accompanied by a high production of H2. The ability of Ni/CeZrO2 to be regenerated is its main advantage over the Ni-MgO catalyst that is popular for CNT production. This paper also shows that the Ni/CeZrO2 catalyst has the potential to be used for CNT and H2 production in a larger scale process, e.g., in a fluidized bed reactor

Toluene Steam Reforming over Ni/CeZrO2—The Influence of Steam to Carbon Ratio and Contact Time on the Catalyst Performance and Carbon Deposition

The formation of tars during coal or biomass gasification is a serious issue resulting in decreasing efficiency of the process and increased maintenance costs. The decomposition of tars can be conducted via catalytic steam reforming that enriches the produced gas in hydrogen. Nevertheless, the catalyst should be characterized by high activity, stability, and resistance towards carbon deposition. Ceria-zirconia supported nickel (Ni/CeZrO2) is a very good candidate to catalyze tar removal—Ni is an active phase for reforming reactions, while CeZrO2 provides the active sites that play important roles in protecting the catalyst from carbon deposition. Ni/CeZrO2 shows high activity in the steam reforming of model tar compounds. In this paper, its performance in the steam reforming of toluene and carbon deposition is discussed considering the changing parameters of the reaction: the temperature, steam to carbon ratio, and the contact time

CNT and H2 Production during CH4 Decomposition over Ni/CeZrO2. II. Catalyst Performance and Its Regeneration in a Fluidized Bed

In this work, a ceria-zirconia supported nickel catalyst (Ni/CeZrO2) was for the first time used in a fluidized bed reactor in order to obtain carbon nanotubes (CNTs) and H2 in the reaction of the decomposition of CH4. The same catalyst was afterward regenerated with H2O, which was accompanied with the production of H2. The impact of catalyst granulation, temperature, and gas hourly space velocity (GHSV) on the amount and type of carbon deposits was determined using thermogravimetric analysis (TGA) and scanning and transmission electron microscopy (SEM and TEM). The presence of randomly oriented and curved CNTs with an outer diameter of up to 64 nm was proved. The Ni/CeZrO2 particles were loosely covered with CNTs, freely dispersed over CNTs, and strongly attached to the external CNT walls. TEM proved the presence of a Ni/CeZrO2@CNT hybrid material that can be further used as catalyst, e.g., in WGS or DRM reactions. The impact of GHSV on hydrogen production during catalyst regeneration was determined. The catalyst was subjected to cyclic tests of CH4 decomposition and regeneration. According to the obtained results, Ni/CeZrO2 can be used in CH4 conversion to CNTs and H2 (instead of CH4 combustion), e.g., in the vicinity of installations that require methane utilization

Characterization of CeO₂, ZrO₂, and CeZrO₂ crystals on CNT

Carbon nanotubes are increasingly being used as a support for catalyst particles. Carbon nanotubes are also used for filtering and reduction, their widespread use due to the high surface area which allows for attachment to the surface of carbon nanotubes a large amount of metallic (Ni, Fe, Pt, etc.) or oxide particles, serving as catalysts. The use of ceria-zirconia mixed oxide deposited on the surface of the nanotubes has not yet been sufficiently examined. Scanning transmission electron microscope with high-angle annular dark-field imaging and high-resolution transmission electron microscopy imaging were used as primary research techniques. Conducted research using high-angle annular dark-field imaging allows determining that catalyst particles have a regular shape which is the best from the standpoint of catalysis. Using a fast Fourier transform: and diffraction pattern has identified the catalyst particles as CeZrO₂

The Impact of Electromobility in Public Transport in EU Member States on Greenhouse Gas Emission

Celem artykułu jest ocena emisji gazów cieplarnianych elektrycznych autobusów miejskich w państwach członkowskich Unii Europejskiej. W pracy przedstawiono wyniki oceny emisji gazów cieplarnianych w następstwie ładowania akumulatorów autobusów miejskich z wykorzystaniem sieci elektroenergetycznej w poszczególnych krajach. Analizy obejmowały ramy czasowe od 2015 do 2050 r. Wykonano również analizę porównawczą emisji gazów cieplarnianych autobusu elektrycznego oraz autobusu z silnikiem spalinowym.The paper presents the results of the greenhouse gas emission assessment for charging city bus batteries using the power grid in each EU country. The analysis covered the time frame from 2015–2050. A comparative analysis of greenhouse gas emissions of an electric bus and a bus with an internal combustion engine was also carried out

On the HKUST-1/GO and HKUST-1/rGO Composites: The Impact of Synthesis Method on Physicochemical Properties

The chemical stability and adsorptive/catalytic properties of the most widely studied metal–organic framework (MOF), which is HKUST-1, can be improved by its combination with graphene oxide (GO) or reduced graphene oxide (rGO). The chemistry of GO or rGO surfaces has a significant impact on their interaction with MOFs. In this work, we demonstrate that GO and rGO interaction with HKUST-1 influences the morphology and textural properties but has no impact on the thermal stability of the final composites. We also show that synthesis environment, e.g., stirring, to some extent influences the formation of HKUST-1/GO and HKUST-1/rGO composites. Homogeneous samples of the sandwich-type composite can be obtained when using reduced graphene oxide decorated with copper (Cu/rGO), which, owing to the presence of Cu sites, allows the direct crystallisation of HKUST-1 and its further growth on the graphene surface. This work is the first part of our research on HKUST-1/GO and HKUST-1/rGO and deals with the influence of the type of graphene material and synthesis parameters on the composites’ physicochemical properties that were determined by using X-ray diffraction, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis