Synthesis and Application of Metal Mixed Oxide Catalysts (MMOs Catalysts)

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Catalytic Materials".

Deadline for manuscript submissions: closed (10 April 2022) | Viewed by 7185

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Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro, 70125 Bari, Italy
Interests: homogeneous catalysis, heterogeneous catalysis, CO2 conversion; biomass conversion
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Guest Editor
1. Department of Chemistry, University of Bari, 70125 Bari, Italy
2. CIRCC, 70126 Bari, Italy
Interests: catalysis; CO2 conversion; green chemistry; integration of biotechnology and catalysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Heterogeneous catalysis can be considered a pillar of chemical and energy industries. Catalysis by metal oxides (MOs) or mixed metal oxides (MMOs) plays a key role, as it covers a variety of processes and offers the advantages of easy recoverability of catalysts, large surface properties variability and a relatively low preparation cost. MMOs are easily prepared by combinations of two or more (transition) metal oxides in different proportions and stoichiometry, both in crystalline or amorphous form, exploiting the synergism of the surface functions of single metal oxides to increase the activity, selectivity, and stability of the catalyst. They are significantly more complex than metal-based catalysts, with the possible presence of multiple oxidation states and acid/base functionalities, variable local coordination, coexisting bulk, and surface phases and one of the components can operate also as a support. Their high versatility makes them usable for a wide range of catalytic reactions such as selective oxidation and reduction reactions, in thermo-, electro- and photo-catalysis. They apply to the synthesis of a variety of chemicals ranging from pharmaceuticals to intermediates and bulk chemicals. Several methods are used for their preparation which confer to the synthesized MMOs specific characteristics. among them sol–gel, wet impregnation or co-precipitation, hydrothermal methods, microwave irradiation and mechanochemistry are the most used methods. The molecular structures of the MMOs can be characterized with different spectroscopic surface or bulk techniques and using chemi/physisorption methods. This special issue will describe the most advanced synthetic methodologies of mixed oxides, the new characterization techniques, and their application in catalysis.

Considered your expertise in the field, we are pleased to invite you to submit a contribution to this special issue as original research paper, communication, mini review, or review.

Dr. Francesco Nocito
Prof. Dr. Angela Dibenedetto
Guest Editors

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Keywords

  • Heterogeneous catalysis
  • MMOs applications
  • MMOs synthetic procedure and characterization
  • Oxidation reactions MMOs assisted
  • Reduction reactions MMOs assisted

Published Papers (3 papers)

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Research

23 pages, 8445 KiB  
Article
Synthetic Routes to Crystalline Complex Metal Alkyl Carbonates and Hydroxycarbonates via Sol–Gel Chemistry—Perspectives for Advanced Materials in Catalysis
by Schirin Hanf, Carlos Lizandara-Pueyo, Timo Philipp Emmert, Ivana Jevtovikj, Roger Gläser and Stephan Andreas Schunk
Catalysts 2022, 12(5), 554; https://doi.org/10.3390/catal12050554 - 18 May 2022
Cited by 3 | Viewed by 2150
Abstract
Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after [...] Read more.
Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after hydrolysis of the precursors. In our contribution we have therefore shown three different solubilization strategies for metal alkoxides, namely the derivatization, the hetero-metallization and CO2 insertion. The latter strategy leads to a stoichiometric insertion of CO2 into the metal–oxygen bond of the alkoxide and the subsequent formation of metal alkyl carbonates. These precursors can then be employed advantageously in sol–gel chemistry and, after controlled hydrolysis, result in chemically defined crystalline carbonates and hydroxycarbonates. Cu- and Zn-containing carbonates and hydroxycarbonates were used in an exemplary study for the synthesis of Cu/Zn-based bulk catalysts for methanol synthesis with a final comparable catalytic activity to commercial standard reference catalysts. Full article
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11 pages, 2374 KiB  
Article
Tuning the Electronic Structure of CoO Nanowire Arrays by N-Doping for Efficient Hydrogen Evolution in Alkaline Solutions
by Maoqi Cao, Xiaofeng Li, Dingding Xiang, Dawang Wu, Sailan Sun, Hongjing Dai, Jun Luo and Hongtao Zou
Catalysts 2021, 11(10), 1237; https://doi.org/10.3390/catal11101237 - 14 Oct 2021
Cited by 4 | Viewed by 1891
Abstract
Electrochemical hydrogen evolution reactions (HER) have drawn tremendous interest for the scalable and sustainable conversion of renewable electricity to clear hydrogen fuel. However, the sluggish kinetics of the water dissociation step severely restricts the high production of hydrogen in alkaline media. Tuning the [...] Read more.
Electrochemical hydrogen evolution reactions (HER) have drawn tremendous interest for the scalable and sustainable conversion of renewable electricity to clear hydrogen fuel. However, the sluggish kinetics of the water dissociation step severely restricts the high production of hydrogen in alkaline media. Tuning the electronic structure by doping is an effective method to boost water dissociation in alkaline solutions. In this study, N-doped CoO nanowire arrays (N-CoO) were designed and prepared using a simple method. X-ray diffraction (XRD), element mappings and X-ray photoelectron spectroscopy (XPS) demonstrated that N was successfully incorporated into the lattice of CoO. The XPS of Co 2p and O 1s suggested that the electronic structure of CoO was obviously modulated after the incorporation of N, which improved the adsorption and activation of water molecules. The energy barriers obtained from the Arrhenius relationship of the current density at different temperatures indicated that the N-CoO nanowire arrays accelerated the water dissociation in the HER process. As a result, the N-CoO nanowire arrays showed an excellent performance of HER in alkaline condition. At a current density of 10 mA cm−1, the N-CoO nanowire arrays needed only a 123 mV potential, which was much lower than that of CoO (285 mV). This simple design strategy provides some new inspiration to promote water dissociation for HER in alkaline solutions at the atomic level. Full article
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17 pages, 3382 KiB  
Article
Selective Catalytic Reduction of NO by NH3 over Mn–Cu Oxide Catalysts Supported by Highly Porous Silica Gel Powder: Comparative Investigation of Six Different Preparation Methods
by Davyd Urbanas and Edita Baltrėnaitė-Gedienė
Catalysts 2021, 11(6), 702; https://doi.org/10.3390/catal11060702 - 01 Jun 2021
Cited by 4 | Viewed by 2123
Abstract
In this study, Mn-based catalysts supported by highly porous silica gel powder (SSA up to 470 m2·g−1 and total pore volume up to 0.8 cm3·g−1) were prepared by six different methods in liquid solutions (electroless metal [...] Read more.
In this study, Mn-based catalysts supported by highly porous silica gel powder (SSA up to 470 m2·g−1 and total pore volume up to 0.8 cm3·g−1) were prepared by six different methods in liquid solutions (electroless metal deposition, stepwise addition of a reducing agent, wet impregnation, incipient wetness impregnation, urea hydrolysis, and ammonia evaporation) and tested for selective catalytic reduction of NOx with ammonia (NH3-SCR de-NOx). Prior to the activity test all the catalysts prepared were characterized by ICP-OES, SEM, EDX mapping, XPS, XRD and N2 adsorption techniques to provide the comprehensive information about their composition and morphology, investigate the dispersion of active components on the carrier surface, identify the chemical forms and structural properties of the catalytically active species of the catalysts prepared. The results revealed that all the methods applied for preparation of SCR de-NOx catalysts can ensure the uniform distribution of Mn species on the carrier surface, however as it is typical for preparation techniques in a liquid phase the significant reduction in SSA and pore volume along with increasing the loading was observed. Considering both the physicochemical properties and the catalytic performance of the catalysts the least effective preparation method was shown to be ammonia evaporation, while the most attractive techniques are incipient wetness impregnation and electroless metal deposition. Full article
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