Editorial

4 pages, 216 KiB

Open AccessEditorial

Catalysts for Air Pollution Control: Present and Future

by Juan Pablo Bortolozzi, Ezequiel David Banús and Eduardo Miró

Catalysts 2023, 13(9), 1264; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13091264 - 01 Sep 2023

Cited by 1 | Viewed by 1218

Due to the continuous increase in both industrial activities and in the use of internal combustion engines, the quality of atmospheric air has progressively deteriorated, both in urban conglomerates and globally [...] Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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19 pages, 4320 KiB

Open AccessEditor’s ChoiceArticle

Novel Control System Strategy for the Catalytic Oxidation of VOCs with Heat Recovery

by Angel Federico Miranda, María Laura Rodríguez, Federico Martin Serra and Daniel Oscar Borio

Catalysts 2023, 13(5), 897; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13050897 - 16 May 2023

Cited by 1 | Viewed by 1043

Abstract

A theoretical study of the dynamic closed-loop behaviour of a reactor/feed-effluent heat exchanger (FEHE)/furnace system for the catalytic combustion of volatile organic compounds (VOCs) is presented. A 1D pseudohomogeneous plug-flow model is proposed to simulate the non-steady-state operation of the monolith reactor and [...] Read more.

A theoretical study of the dynamic closed-loop behaviour of a reactor/feed-effluent heat exchanger (FEHE)/furnace system for the catalytic combustion of volatile organic compounds (VOCs) is presented. A 1D pseudohomogeneous plug-flow model is proposed to simulate the non-steady-state operation of the monolith reactor and the FEHE, while the furnace behaviour is described by means of a heterogeneous model of lumped parameters. Positive energy feedback is a source of instability that leads to strong thermal oscillations (limit cycles) and may cause damage to the equipment and sintering of the catalyst. The design of a robust and flexible control system and an efficient control strategy are, therefore, required to ensure safe and stable operation. The response of the system under three different control strategies to the most frequent disturbance variables—the feed flowrate (F_V₀) and feed concentration of VOCs (C_0Et)—was evaluated. One of the control strategies consisted of a single-loop feedback system with servomechanism changes in the reactor inlet temperature (T₀) that manipulated the bypass valve and, sequentially, the natural gas flowrate in the furnace (F_NG). This approach made it possible to meet the control objective (reducing VOCs) without losing controllability and while minimizing the use of external fuel. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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18 pages, 11875 KiB

Open AccessEditor’s ChoiceArticle

Catalytic Oxidation of VOC over Cobalt-Loaded Hierarchical MFI Zeolite

by Bozhidar Grahovski, Ralitsa Velinova, Pavletta Shestakova, Anton Naydenov, Hristo Kolev, Iliyana Yordanova, Georgi Ivanov, Krasimir Tenchev and Silviya Todorova

Catalysts 2023, 13(5), 834; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13050834 - 03 May 2023

Cited by 1 | Viewed by 1695

Abstract

The zeolites ZSM-5 with different Si/Al ratios were modified with a buffer solution of HF and NH₄F. This acidic treatment led to the obtaining of a material with secondary mesoporosity. The deposition of cobalt from an aqueous solution of cobalt acetate [...] Read more.

The zeolites ZSM-5 with different Si/Al ratios were modified with a buffer solution of HF and NH₄F. This acidic treatment led to the obtaining of a material with secondary mesoporosity. The deposition of cobalt from an aqueous solution of cobalt acetate on the surface of treated samples generates the formation of different cobalt oxide species: bulk-like Co₃O₄ phases strongly interacting with the support, Co²⁺ in ion exchange positions (γ and β sites) and silicate-like phases. The mechanism of cobalt silicate phase formation is proposed here and includes a replacement of silanol groups and the bridging hydrogens by Co and the inclusion of the Co atoms in tetrahedral framework positions. The catalysts, obtained through use of the treated ZSM-5, exhibit higher activity in the reactions of propane, and n-hexane completes oxidation compared with the catalyst samples containing un-treated zeolite. Both the finer dispersion of metal oxide particles on the hierarchical sample and the presence of secondary mesoporosity improve the effectiveness of the active phase utilization via access to larger number of active sites. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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17 pages, 3730 KiB

Open AccessFeature PaperArticle

The Effect of Metal Ratio and Precipitation Agent on Highly Active Iron-Manganese Mixed Metal Oxide Catalysts for Propane Total Oxidation

by Parag M. Shah, Liam A. Bailey, David J. Morgan and Stuart H. Taylor

Catalysts 2023, 13(5), 794; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13050794 - 23 Apr 2023

Cited by 2 | Viewed by 2217

Abstract

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe_0.50Mn_0.50O_x catalyst was the most active, and this was due to increased surface [...] Read more.

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe_0.50Mn_0.50O_x catalyst was the most active, and this was due to increased surface area along with the formation of a Mn₂O₃ phase that was not present in the other catalysts. The effect of the precipitating agent was evaluated with the Fe_0.50Mn_0.50O_x catalyst, investigating preparation using (NH₄)₂CO₃, K₂CO₃, NH₄OH, KOH, and NaOH. In almost all cases, the activity of propane oxidation was increased compared to the Na₂CO₃-prepared catalyst, with the hydroxide-precipitated catalysts generally being more active than the carbonates. The NH₄OH catalyst was the best performing and this was thought to be due to the formation of a highly active mixed defect spinel structure. Results demonstrate that highly active mixed metal oxide total oxidation catalysts can be prepared using abundant elements, and the choice of precipitating agent is important to maximise the activity. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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22 pages, 9811 KiB

Open AccessFeature PaperArticle

Pt/CeMnO_x/Diatomite: A Highly Active Catalyst for the Oxidative Removal of Toluene and Ethyl Acetate

by Linlin Li, Yuxi Liu, Jiguang Deng, Lin Jing, Zhiquan Hou, Ruyi Gao and Hongxing Dai

Catalysts 2023, 13(4), 676; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13040676 - 30 Mar 2023

Cited by 3 | Viewed by 1328

Abstract

Pt nanoparticles and a CeMnO_x composite were loaded on the surface of the natural diatomite material to generate the Pt/CeMnO_x/diatomite using the redox precipitation and impregnation methods. The physicochemical properties of the catalysts were characterized by means of various techniques. [...] Read more.

Pt nanoparticles and a CeMnO_x composite were loaded on the surface of the natural diatomite material to generate the Pt/CeMnO_x/diatomite using the redox precipitation and impregnation methods. The physicochemical properties of the catalysts were characterized by means of various techniques. The catalytic properties and resistance to H₂O and SO₂ of the catalysts were measured for the oxidation of typical volatile organic compounds (i.e., toluene and ethyl acetate). Among all of the as-prepared samples, Pt/CeMnO_x/diatomite exhibited the highest catalytic activity: the temperatures (T_90%) at a toluene or ethyl acetate conversion of 90% were 230 and 210 °C at a space velocity (SV) of 20,000 mL g⁻¹ h⁻¹, respectively, and the turnover frequency (TOF_Pt) at 220 °C was 1.04 μmol/(g_cat s) for ethyl acetate oxidation and 1.56 μmol/(g_cat s) for toluene oxidation. In particular, this sample showed a superior catalytic activity for ethyl acetate oxidation at low temperatures, with its T_50% being 185 °C at SV = 20,000 mL g⁻¹ h⁻¹. In addition, the Pt/CeMnO_x/diatomite sample possessed good sulfur dioxide resistance during the toluene oxidation process. In the presence of SO₂, some of the SO₂ molecules were adsorbed on diatomite, which protected the active sites from being poisoned by SO₂ to a certain extent. The pathways of ethyl acetate and toluene oxidation over Pt/CeMnO_x/diatomite or Pt/CeMnO_x were as follows: The C–C and C–O bonds in ethyl acetate are first broken to form the CH₃CH₂O* and CH₃CO* species or toluene is first oxidized to benzaldehyde and benzoic acid, and all of these intermediates are then converted to CO₂ and H₂O. This work can provide a strategy to develop efficient catalysts with high catalytic activity, durability, low cost, and easy availability under actual working conditions. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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16 pages, 5833 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Highly Efficient Au/ZnO−ZrO₂ Catalysts for CO Oxidation at Low Temperature

by Roberto Camposeco, Viridiana Maturano-Rojas and Rodolfo Zanella

Catalysts 2023, 13(3), 590; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13030590 - 15 Mar 2023

Cited by 2 | Viewed by 1120

Abstract

A series of gold catalysts on ZnO−ZrO₂ featuring nominal ZnO loads of 3, 5, and 10 wt. % were synthesized by the sol–gel method using Zn(NO₃)₂ and zirconium (IV) propoxide aqueous solutions. In addition, gold catalysts with nominal loads [...] Read more.

A series of gold catalysts on ZnO−ZrO₂ featuring nominal ZnO loads of 3, 5, and 10 wt. % were synthesized by the sol–gel method using Zn(NO₃)₂ and zirconium (IV) propoxide aqueous solutions. In addition, gold catalysts with nominal loads between 1 and 3 wt. % were produced by the method of deposition-precipitation with urea, and their performance in the CO oxidation reaction at low temperature was evaluated. HRTEM outcomes revealed high gold dispersion on the 3Au/5ZnO−ZrO₂ catalyst with Zn/Zr atomic ratio of (5/95) and 3 wt. % of gold, which showed the highest CO conversion at low temperature (−5 °C) under air treatment when the CO oxidation was carried out with a space velocity of ~46,000 h⁻¹. The incorporation of ZnO to ZrO₂ provoked high dispersion of the gold nanoparticles on the support and close size distribution; moreover, the presence of Au¹⁺ and Zr³⁺ species was increased by the Zr−O−Zn interaction, which was stronger than in the single Au/ZrO₂ and Au/ZnO catalysts. DRIFT/GC−MS confirmed that the Au¹⁺/Au⁰ ratio and formation of carbonate species played an important role in determining the CO conversion; likewise, the 3Au/5ZnO–ZrO₂ catalyst was stable at 10 °C for 24 h. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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13 pages, 1601 KiB

Open AccessEditor’s ChoiceArticle

Chlorobenzene Mineralization Using Plasma/Photocatalysis Hybrid Reactor: Exploiting the Synergistic Effect

by N’Zanon Aly KONE, Nacer Belkessa, Youcef Serhane, Sandotin Lassina Coulibaly, Mahamadou Kamagate, Lotfi Mouni, Sivachandiran Loganathan, Lacina Coulibaly, Abdelkrim Bouzaza, Abdeltif Amrane and Aymen Amine Assadi

Catalysts 2023, 13(2), 431; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13020431 - 16 Feb 2023

Cited by 2 | Viewed by 1592

Abstract

Mineralization of gaseous chlorobenzene (major VOC from cement plants) was studied in a continuous reactor using three advanced oxidation processes: (i) photocatalysis, (ii) Dielectric Barrier Discharge (DBD) plasma and (iii) DBD/TiO₂-UV coupling. The work showed an overproduction of OH * and [...] Read more.

Mineralization of gaseous chlorobenzene (major VOC from cement plants) was studied in a continuous reactor using three advanced oxidation processes: (i) photocatalysis, (ii) Dielectric Barrier Discharge (DBD) plasma and (iii) DBD/TiO₂-UV coupling. The work showed an overproduction of OH * and O * radicals in the reaction medium due to the interaction of Cl * and O₃. A parametric study was carried out in order to determine the evolution of the removal efficiency as a function of the concentration, the flow rate and the applied voltage. Indeed, a variation of the flow rate from 0.25 to 1 m³/h resulted in a decrease in the degradation rate from 18 to 9%. Similarly, an increase in concentration from 13 to 100 mg/m³ resulted in a change in degradation rate from 18 to 4%. When the voltage was doubled from 6 to 12 kV, the degradation rate varied from 22 to 29 % (plasma) and from 53 to 75% (coupling) at 13 mg/m³. The evolution of CO_X and O₃ was monitored during the experiments. When the voltage was doubled, the selectivity increased from 28 to 37% in the plasma alone and from 48 to 62 % in the coupled process. In addition, at this same voltage range, the amount of ozone formed varied from 10 to 66 ppm in plasma and 3 to 29 ppm in coupling. This degradation performance can be linked to a synergistic effect, which resulted in an increase in the intensity of the electric field of plasma by the TiO₂ and the improvement in the performance of the catalyst following the bombardment of various high-energy particles of the plasma. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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16 pages, 8469 KiB

Open AccessArticle

Cs_xCo/Na-MOR Coating on Ceramic Monoliths for Co-Adsorption of Hydrocarbons Mixture and Selective Catalytic Reduction of NOx

by Ramiro M. Serra, Leticia E. Gómez, Inés S. Tiscornia, María de los Milagros Deharbe and Alicia V. Boix

Catalysts 2023, 13(1), 106; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13010106 - 03 Jan 2023

Cited by 4 | Viewed by 1264

Abstract

In this work, ceramic monoliths were coated with powders based on exchanged Cs and/or Co cations in Na-mordenite (MOR) zeolite. SEM images showed that zeolite particles fill the macropores of cordierite walls and form a continuous layer of approximately 40 µm with good [...] Read more.

In this work, ceramic monoliths were coated with powders based on exchanged Cs and/or Co cations in Na-mordenite (MOR) zeolite. SEM images showed that zeolite particles fill the macropores of cordierite walls and form a continuous layer of approximately 40 µm with good adherence. XPS analysis revealed that Co and Cs are present on the film surface solely as Co²⁺ and Cs⁺ at exchange positions in zeolite. The monolithic structures were evaluated for the butane-toluene co-adsorption and SCR of NOx with hydrocarbon mixture as the reducing agent. The presence of alkali metal cations in the zeolitic lattice favored the adsorption capacity of both hydrocarbons, while cobalt cations provoked a decrease in the adsorbed amounts due to its weak interaction with the HCs. Breakthrough curves of butane adsorption showed a roll-up phenomenon, associated with a competitive adsorption effect generated from toluene presence. In the desorption process, it was observed that adsorbed toluene hindered the butane diffusion through mordenite channels, which released at higher temperatures (above 250 °C). Cs₂CoM and Cs₇CoM monoliths were more active than the CoM monolith for NO-SCR. The presence of Cs cations close to Co cations increased the hydrocarbons concentration around active sites at high temperatures, according to TPD results, promoting the reduction activity of NO. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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23 pages, 7179 KiB

Open AccessArticle

Highly Resistant LaCo_1−xFe_xO₃ Perovskites Used in Chlorobenzene Catalytic Combustion

by Héctor Acosta Pérez, Carlos A. López, Octavio J. Furlong, Marcelo S. Nazzarro, Sergio G. Marchetti, Luis E. Cadús and Fabiola N. Agüero

Catalysts 2023, 13(1), 42; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13010042 - 25 Dec 2022

Cited by 3 | Viewed by 1583

Abstract

The stability of LaCo_1−xFe_xO₃ perovskite structures (x = 0; 0.25; 0.5; 0.75; 1) was studied in the combustion of chlorobenzene. This family of catalysts was synthesized by the citrate method obtaining pure structures. The Fe doping in the [...] Read more.

The stability of LaCo_1−xFe_xO₃ perovskite structures (x = 0; 0.25; 0.5; 0.75; 1) was studied in the combustion of chlorobenzene. This family of catalysts was synthesized by the citrate method obtaining pure structures. The Fe doping in the original structure induces electronic environments capable of generating the Co²⁺/Co³⁺ redox couple. The characteristics observed in bulk are perfectly reflected on the surface, favoring a high resistance of the solids to chlorine poisoning. Superior stability under reaction conditions was observed in the phase with the lowest Fe content (x = 0.25), remaining stable at 100% combustion of chlorobenzene during 100 h, not observing intermediate reaction products. These results open up a new avenue for designing and fabricating high-performance catalysts in the environmental field Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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25 pages, 8379 KiB

Open AccessEditor’s ChoiceArticle

Activity of Catalytic Ceramic Papers to Remove Soot Particles—A Study of Different Types of Soot

by Sabrina Antonela Leonardi, Eduardo Ernesto Miró and Viviana Guadalupe Milt

Catalysts 2022, 12(8), 855; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12080855 - 03 Aug 2022

Cited by 5 | Viewed by 1784

Abstract

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In [...] Read more.

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In this work, programmed temperature oxidation (TPO) experiments were carried out using Co,Ce or Co,Ba,K catalysts supported on ceramic papers. Soot particles were obtained by burning diesel fuel in a vessel (LabSoot) or by filtering exhaust gases from a turbo diesel engine in a DPF filter (BenchSoot), and compared with a commercial diesel soot: Printex U. Various characterization techniques were useful to relate the characteristics of both the soot particles and the catalysts with the TPO results. The maximum catalytic soot burn rate (T_M) temperatures were in the range of diesel exhaust temperatures that would facilitate in-situ regeneration of the DPF. The Co,Ba,K catalyst showed a higher catalytic effect in LabSoot, as the latter exhibited the largest primary particles and the higher order of graphene layers, for which the potassium-containing catalyst improves the contact between soot and catalyst and favors the combustion of soot, while the Co,Ce catalyst preferentially enhanced the combustion of commercial soot by supplying active oxygen. Full article

(This article belongs to the Special Issue Catalysts for Air Pollution Control: Present and Future)

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