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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 October 2022) | Viewed by 26450

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Special Issue Editors

Dr. Bozhidar Stefanov

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Guest Editor

Department of Chemistry, Faculty of Electronic Engineering and Technologies, Technical University of Sofia, Sofia, Bulgaria
Interests: photocatalysts; thin films; sol-gel deposition; computational modeling; FTIR; Raman spectroscopy; photoelectrocatalysis; photodeposition; functionalization of photocatalysts; optical properties; optical modeling of thin films
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Dr. İlknur Bayrak Pehlivan

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Co-Guest Editor

Department of Materials Science and Engineering, Solid State Physics, Uppsala University, Box 35, 751 03 Uppsala, Sweden
Interests: electrocatalysis; electrochemical ammonia synthesis; direct ammonia fuel cell; high entropy alloys; solar water splitting; electrochromism

Prof. Dr. Silvia Todorova

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Co-Guest Editor

Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: heterogeneous catalysis; complete oxidation of volatile organic compounds; in situ infrared spectroscopy; characterization of new catalysts by different methods (FTIR, TPR, solid-state NMR, XRD, XPS, and adsorption); catalysis of supported metal on porous materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Heterogeneous catalysis has seen a surge in academic interest due to its important applications, such as renewable-energy conversion, environmental remediation, organic products synthesis and transformations, green catalysis, and many others. Although unnoticed on its own, symmetry and its implications is often a main topic of research in the field of catalysis. Hence, this Special Issue of Symmetry is dedicated to the theme “Heterogeneous Catalysis: Topics and Advances.”

The issue is open to submissions covering any aspects of heterogeneous catalysis, fundamental or practical. Special attention will be paid to research, focused on the the implications of symmetry in catalysis, such as (but not limited to): effects of crystallographic structure, shape and orientation on catalytic activity; effects of substrate symmetry in catalysis; symmetric/asymmetric activity and reaction pathways in catalysts; effects of support morphology and structure on catalytic activity (e.g., photonic effects in photocatalysts supported on highly-ordered substrate), etc.

Dr. Bozhidar Stefanov
Dr. İlknur Bayrak Pehlivan
Dr. Silvia Todorova
Guest Editors

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Keywords

heterogeneous catalysis
catalysts structure-activity relationships
symmetric and asymmetric activity in catalysts
shape-selective synthesis of catalysts
catalyst support structure effects on activity
photonic effects in photocatalysis
molecular symmetry effects on catalytic activity

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Published Papers (10 papers)

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Research

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15 pages, 2382 KiB

Open AccessFeature PaperArticle

Tuning the Cu/Ce Ratio for Improved Benzene Oxidation over Gold-Promoted Alumina-Supported CuO-CeO₂

by Tatyana Tabakova, Petya Petrova, Yordanka Karakirova, Georgi Avdeev, Elitsa Kolentsova and Lyuba Ilieva

Symmetry 2023, 15(2), 263; https://doi.org/10.3390/sym15020263 - 17 Jan 2023

Cited by 2 | Viewed by 1619

Abstract

Increased levels and detrimental effects of volatile organic compounds (VOCs) stimulate research efforts to develop catalysts with high efficiency in complete hydrocarbon oxidation. This work is focused on the complete oxidation of benzene as a probe reaction for VOCs elimination over alumina-supported CuO-CeO₂ mixed oxide promoted by gold. The benzene molecule is the most stable among the aromatic hydrocarbons with toxic and often carcinogenic effects known as BTEX (benzene, toluene, ethylbenzene, and xylenes) owing to the symmetry and stability of the benzene ring. Use of low-cost materials as support is an appropriate strategy aimed at improving catalyst economic profitability. The effect of the Cu-Ce ratio, namely 2:1 and 1:5, and the role of supported gold in the catalyst performance were evaluated. Analysis of the impact of support composition in benzene oxidation was based on sample characterization by textural measurements, PXRD, EPR spectroscopy, and the TPR technique. Special attention was paid to the disturbed symmetry of the ceria crystallographic structure by defects formation and its implication for the catalytic activity. Gold on alumina-supported binary oxide catalysts exhibited a significantly higher activity than promoted supported monometallic oxides. The best performance of the Au/Cu-Ce 1:5 sample was related to the highest concentration of paramagnetic Cu²⁺ ions and the best copper species dispersion evidenced by PXRD, EPR, and TPR results. The catalyst achieved stable total oxidation to CO₂ and water by 94% benzene conversion at 250 °C, thus implying the potential of this composition in developing efficient catalytic materials for atmospheric pollutant abatement. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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13 pages, 3012 KiB

Open AccessArticle

Nickel Nanoparticles Anchored on Activated Attapulgite Clay for Ammonia Decomposition to Hydrogen

by Ling-Feng Zhang, Zhong-Pan Hu, Shi-Hang Liang, Feng Xu and Zhong-Yong Yuan

Symmetry 2022, 14(12), 2627; https://doi.org/10.3390/sym14122627 - 12 Dec 2022

Cited by 4 | Viewed by 1906

Abstract

Ammonia decomposition to hydrogen technique is an effectively way to solve the problems associated with the storage and transportation of hydrogen, but the development of a high-performance catalyst for ammonia decomposition is a great challenge. Ni species supported on activated attapulgite clay (AATP) is prepared by a homogeneous precipitation method for ammonia decomposition to CO_x-free H₂. The structural properties of the Ni/AATP catalysts are characterized by thermogravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy, H₂ temperature-programmed reduction, and N₂ sorption technique. It is revealed that the porous structure and high surface area of rod-like symmetric AATP results in highly dispersed NiO particles because the presence of a strong interaction between AATP and NiO particles. In particular, the Si-OH in AATP can react with Ni species, forming Si-O-Ni species at the interface between Ni and AATP. The Ni/AAPT catalysts are used for ammonia decomposition, the 20%-Ni/ATTP catalyst shows a 95.3% NH₃ conversion with 31.9 mmol min⁻¹ g_cat⁻¹ H₂ formation rate at 650 °C. This study opens a new way to utilize natural minerals as an efficient support of catalysts towards ammonia decomposition reaction. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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13 pages, 3327 KiB

Open AccessFeature PaperArticle

Pt-Modified Nano-Sized Mn₂O₃ Oxide Prepared from the Mn₃O₄ Phase with Tetragonal Symmetry for CO Oxidation

by Silviya Todorova, Anton Naydenov, Maya Shopska, Hristo Kolev, Iliyana Yordanova and Krasimir Tenchev

Symmetry 2022, 14(12), 2543; https://doi.org/10.3390/sym14122543 - 1 Dec 2022

Viewed by 1879

Abstract

One of the current problems in the environmental catalysis is the design of an effective and less costly catalytic system for the oxidation of CO. The nano-sized α-Mn₂O₃ oxide has been prepared and modified with 0.5 wt.% Pt. The catalysts have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and diffuse-reflectance infrared spectroscopy (DRIFTS). Finely divided PtO and Pt(OH)₂ are being formed on the Mn₂O₃ surface as a result of the strong interaction between platinum and the nano-oxide. Based on DRIFTS investigations and the model calculations, a Langmuir–Hinshelwood type of mechanism is supposed for CO oxidation on Pt/Mn₂O₃. The CO and oxygen are adsorbed on different types of sites. The Mars–van Krevelen mechanism is the most probable one over pure Mn₂O₃, thus suggesting that CO₂ is adsorbed on the oxidized sites. The CO adsorption in the mixture CO + N₂ or in the presence of oxygen (CO + N₂ + O₂) leads to a partial reduction in the Pt⁺ surface species and the formation of linear Pt¹⁺−CO and Pt⁰−CO carbonyls. Both of them take part in the CO oxidation reaction. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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13 pages, 4870 KiB

Open AccessArticle

Computational Study of H₂ Catalytic Combustion on Pd₃₈ Cluster Model and Pd(111) Slab Model

by Dabin Qi, Xudong Luo, Yulong Yao, Na Qi, Xiaojun Lu, Hao Chen and Hongqi Shi

Symmetry 2022, 14(8), 1544; https://doi.org/10.3390/sym14081544 - 28 Jul 2022

Cited by 1 | Viewed by 1698

Abstract

Hydrogen is one of the exhaust gases produced by nuclear power stations. Due to the potential danger of incomplete combustion and the emission of hydrogen, hydrogen catalytic combustion is introduced to ensure the safety of nuclear power stations. Palladium is a widely used catalyst for hydrogen catalytic combustion. H₂ catalytic combustion on a Pd(111) slab model and Pd₃₈ cluster model were simulated using density functional theory (DFT), in order to analyze the H₂ oxidation mechanism on the catalyst surface. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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14 pages, 2691 KiB

Open AccessArticle

Effect of Zeolite Catalyst on the Pyrolysis Kinetics of Multi-Layered Plastic Food Packaging

by Irma Kremer, Tihomir Tomić, Zvonimir Katančić, Zlata Hrnjak-Murgić, Matko Erceg, Stefano Vecchio Ciprioti and Daniel Rolph Schneider

Symmetry 2022, 14(7), 1362; https://doi.org/10.3390/sym14071362 - 1 Jul 2022

Cited by 11 | Viewed by 2226

Abstract

Pyrolysis is gaining more significance as a technology used to produce alternative fuels and chemicals. This study dealt with the catalytic pyrolysis of a realistic waste mixture of multi-layered plastic food packaging. The thermal behavior, kinetic parameters, and kinetic model of multi-layered plastic food packaging pyrolysis were determined to show its potential for process scale-up. In particular, we aimed to evaluate the effect of a ZSM-5 zeolite catalyst, modified with iron(III) oxide. The pyrolysis process on this decagonal structure was investigated using thermogravimetric analysis under nitrogen flow at four heating rates ranging between 40 and 600 °C. The kinetic study was conducted using the model-free isoconversional Friedman method as well as advanced statistical analysis to determine the reaction mechanism of the process. The thermal decomposition occurred in the range of 350–510 °C, with a mass loss greater than 90%. The kinetic study revealed a complex pyrolysis process, which consisted of three decomposition stages, diffusion, and Avrami-Erofeev reaction types. The activation energy values determined by the Friedman method rose with the degree of conversion, from 127 kJ mol⁻¹ at 0.01 to 219 kJ mol⁻¹ at 0.95. The doping of the catalyst lowered the activation energy of the reaction by 44% and 8% in the first and second stages, respectively, and increased the acidity of the zeolites, thus enhancing the reactivity on the surface of the catalysts. Lower activation energy meant less energy was required to heat the pyrolysis reactor since the onset temperature of sample decomposition was reduced. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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20 pages, 5398 KiB

Open AccessArticle

Design Control of Copper-Doped Titania–Zirconia Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

by Tanya Tsoncheva, Gloria Issa, Radostina Ivanova, Momtchil Dimitrov, Daniela Kovacheva, Genoveva Atanasova and Jiří Henych

Symmetry 2022, 14(4), 751; https://doi.org/10.3390/sym14040751 - 6 Apr 2022

Cited by 4 | Viewed by 2053

Abstract

This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO₂–TiO₂ mixed oxides with diverse compositions, followed by the consecutive chemisorption and hydrolysis of copper ammonia complexes on them. The nitrogen physisorption, XRD, SEM, HRTEM, TPR, XPS, UV-Vis, and Raman spectroscopies were applied for the catalysts’ characterization. Methanol decomposition and the total oxidation of ethyl acetate, both of which with potential for sustainable environmental protection, were used as catalytic tests. The complex relationship between the phase composition, structure, and morphology of titania–zirconia mixed oxides and the state and catalytic behavior of the copper oxide species supported on them was investigated. In comparison with the conventional impregnation technique, the novel preparation procedure revealed the generation of more uniform and homogeneously dispersed needle-like copper oxide crystallites in the mesoporous TiO₂–ZrO₂ host matrix, which typically ensure improved catalytic performance. The synergistic activity between the loaded copper species and TiO₂–ZrO₂ support was discussed. All ternary composites exhibited superior catalytic activity in total oxidation of ethyl acetate. The specific behavior of the catalysts in methanol decomposition was related to the irreversible phase transformations by the influence of the reaction medium. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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16 pages, 5413 KiB

Open AccessArticle

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

by Marcin Janczarek, Zhishun Wei, Tharishinny R. Mogan, Lei Wang, Kunlei Wang, Akio Nitta, Bunsho Ohtani and Ewa Kowalska

Symmetry 2021, 13(9), 1682; https://doi.org/10.3390/sym13091682 - 12 Sep 2021

Cited by 3 | Viewed by 2053

Abstract

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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18 pages, 3466 KiB

Open AccessArticle

Design and Catalytic Behaviour of Hosted in Activated Carbon Foam Co_xZn_1−xFe₂O₄ Ferrites

by Tanya Tsoncheva, Radostina Ivanova, Nikolay Velinov, Daniela Kovacheva, Ivanka Spassova, Daniela Karashanova and Nartzislav Petrov

Symmetry 2021, 13(8), 1532; https://doi.org/10.3390/sym13081532 - 20 Aug 2021

Cited by 1 | Viewed by 2213

Abstract

Carbon foams with different surface functionality and tailored texture characteristics were prepared from mixtures containing coal tar pitch and furfural in different proportions. The obtained materials were used as a host matrix for the preparation of zinc- and cobalt-mixed ferrite nanoparticles. The texture, morphology, phase composition, and the related redox and catalytic properties of the obtained composites were characterized by low-temperature nitrogen physisorption, XRD, SEM, HRTEM, FTIR, Mössbauer spectroscopy, TPR and catalytic decomposition of methanol to syngas. The impact of the carbon support on the formation of Co- and Zn-mixed ferrites was discussed in detail using KIT-6 silica-based modifications as reference samples. The catalytic behavior of the ferrites was considered in a complex relation to their composition, morphology, location in the porous matrix and metal ions distribution in the spinel sub-lattices. The higher amount of furfural in the carbon foam precursor promoted the formation of cobalt-rich, more accessible and highly active methanol decomposition to syngas spinel particles. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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9 pages, 2902 KiB

Open AccessArticle

Effects of Anodic Aluminum Oxide Substrate Pore Geometry on the Gas-Phase Photocatalytic Activity of ZnO/Al₂O₃ Composites Prepared by Atomic Layer Deposition

by Bozhidar I. Stefanov, Blagoy S. Blagoev, Lars Österlund, Boriana R. Tzaneva and George V. Angelov

Symmetry 2021, 13(8), 1456; https://doi.org/10.3390/sym13081456 - 9 Aug 2021

Cited by 7 | Viewed by 2174

Abstract

We report on the photocatalytic activity of ZnO layers deposited by atomic layer deposition on a porous anodic aluminum oxide substrate with hexagonal pore symmetry and varied pore dimensions. ZnO/Al₂O₃ composites were prepared with pore diameters in the range 93–134 nm and interpore distance in the range 185–286 nm, and their photocatalytic activity was measured for gas-phase photocatalytic oxidation of acetaldehyde at varying UV illumination intensities (0.08–3.94 mW cm⁻²). The results show that substrates with narrower pore diameters (<115 nm, in the case of this study) have a detrimental effect on the photocatalyst performance, despite their higher effective surface. The results are explained on the basis of limited mass transfer inside the porous structure and can be used as a guideline in the purposeful design of photocatalysts with a nanoporous or nanotubular structure. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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Review

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19 pages, 1206 KiB

Open AccessFeature PaperReview

Catalytic Pyrolysis of Plastic Waste and Molecular Symmetry Effects: A Review

by Saša Papuga, Milica Djurdjevic, Andrea Ciccioli and Stefano Vecchio Ciprioti

Symmetry 2023, 15(1), 38; https://doi.org/10.3390/sym15010038 - 23 Dec 2022

Cited by 20 | Viewed by 6470

Abstract

The present review addresses the latest findings and limitations in catalytic pyrolysis for the processing of plastic waste into valuable fuels. Compared to thermal degradation of plastics, catalytic pyrolysis provides better results in regards to the quality of the obtained liquid hydrocarbon fuel. Different types of catalysts can be used in order to improve the thermal degradation of plastics. Some of the most used catalysts are different types of zeolites (HUSY, HZSM-5, H

β

), Fluid Catalytic Cracking (FCC), silica-alumina catalysts, or natural clays. There is a need to find affordable and effective catalysts in the aim of achieving commercialization of catalytic pyrolysis of plastic waste. Therefore, this study summarizes and presents the most significant results found in the literature in regards to catalytic pyrolysis. This paper also investigates the symmetry effects of molecules on the pyrolysis process. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis: Topics and Advances)

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