Research

30 pages, 16558 KiB

Open AccessFeature PaperArticle

Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO₂

by Caleb Daniel Watson, Michela Martinelli, Donald Charles Cronauer, A. Jeremy Kropf and Gary Jacobs

Catalysts 2021, 11(2), 210; https://doi.org/10.3390/catal11020210 - 05 Feb 2021

Cited by 8 | Viewed by 2369

Abstract

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which [...] Read more.

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO₂ is examined herein. Pt/ZrO₂ catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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10 pages, 1145 KiB

Open AccessArticle

Water–Gas Shift Activity of Pt Catalysts Prepared by Different Methods

by Hilde Bjørkan, Magnus Rønning, Hilde J. Venvik, Tue Johannessen and Anders Holmen

Catalysts 2020, 10(10), 1132; https://doi.org/10.3390/catal10101132 - 01 Oct 2020

Cited by 2 | Viewed by 1935

Abstract

Platinum supported on ceria and zirconia was prepared through different preparation methods: Coprecipitation (CP), spray drying (SD), and flame spray pyrolysis (FSP). The catalysts were characterized by XRD, TPR, N₂ adsorption, and H₂ chemisorption, and the water–gas shift activity in the [...] Read more.

Platinum supported on ceria and zirconia was prepared through different preparation methods: Coprecipitation (CP), spray drying (SD), and flame spray pyrolysis (FSP). The catalysts were characterized by XRD, TPR, N₂ adsorption, and H₂ chemisorption, and the water–gas shift activity in the range 190–310 °C and initial stability at 300–310 °C were tested. Although the spray-dried Pt/CeO₂/ZrO₂ catalyst shows the highest initial activity, it deactivates rapidly at 300 °C and levels out at similar activity as the coprecipitated Pt/CeO₂ and Pt/CeO₂/ZrO₂ within a few hours. Flame spray pyrolysis appears to be a promising preparation method concerning the stability of catalysts, although the initial activity is rather poor. High activity is related to high Pt dispersion, low reduction temperature, and small support particles. The support particle size is also much affected by the preparation method. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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14 pages, 7483 KiB

Open AccessArticle

Zn-Al Mixed Oxides Decorated with Potassium as Catalysts for HT-WGS: Preparation and Properties

by Katarzyna Antoniak-Jurak, Paweł Kowalik, Kamila Michalska, Wiesław Próchniak and Robert Bicki

Catalysts 2020, 10(9), 1094; https://doi.org/10.3390/catal10091094 - 21 Sep 2020

Cited by 7 | Viewed by 2737

Abstract

A set of ex-ZnAl-LDHs catalysts with a molar ratio of Zn/Al in the range of 0.3–1.0 was prepared using co-precipitation and thermal treatment. The samples were characterized using various methods, including X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), [...] Read more.

A set of ex-ZnAl-LDHs catalysts with a molar ratio of Zn/Al in the range of 0.3–1.0 was prepared using co-precipitation and thermal treatment. The samples were characterized using various methods, including X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy FT-IR, N₂ adsorption, Temperature-programmed desorption of CO₂ (TPD-CO₂) as well as Scanning electron microscopy (SEM-EDS). Catalyst activity and long-term stability measurements were carried out in a high-temperature water–gas shift (HT-WGS) reaction. Mixed oxide catalysts with various Zn/Al molar ratios decorated with potassium showed high activity in the HT-WGS reaction within the temperature range of 330–400 °C. The highest activity was found for the Zn/Al molar ratio of 0.5 corresponding to spinel stoichiometry. However, the catalyst with a stoichiometric spinel molar ratio of Zn/Al (ZnAl_0.5_K) revealed a higher tendency for surface migration and/or vaporization of potassium during overheating at 450 °C. The correlation of the activity results and TPD-CO₂ data show that medium basic sites enhance the progress of the HT-WGS reaction. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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19 pages, 5418 KiB

Open AccessFeature PaperArticle

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

by Xinhui Sun, Antonios Arvanitis, Devaiah Damma, Noe T. Alvarez, Vesselin Shanov, Panagiotis G. Smirniotis and Junhang Dong

Catalysts 2020, 10(8), 927; https://doi.org/10.3390/catal10080927 - 12 Aug 2020

Cited by 3 | Viewed by 3338

Abstract

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H₂ and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H₂-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further [...] Read more.

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H₂ and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H₂-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH₄, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH₄, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe³⁺/Fe²⁺ and Cr⁶⁺/Cr³⁺ in WGS membrane reaction while further reduction of Fe²⁺ to Fe⁰ occurred in the CO/CH₄ dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH₄ mixture containing 500 ppmv H₂S also resulted in high-quality MWCNTs similar to those from the H₂S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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18 pages, 5543 KiB

Open AccessArticle

Elucidation of Water Promoter Effect of Proton Conductor in WGS Reaction over Pt-Based Catalyst: An Operando DRIFTS Study

by Lole Jurado, Nuria García-Moncada, Luis F. Bobadilla, Francisca Romero-Sarria and José A. Odriozola

Catalysts 2020, 10(8), 841; https://doi.org/10.3390/catal10080841 - 25 Jul 2020

Cited by 3 | Viewed by 3562

Abstract

A conventional Pt/CeO₂/Al₂O₃ catalyst physically mixed with an ionic conductor (Mo- or Eu-doped ZrO₂) was tested at high space velocity (20,000 h⁻¹ and 80 L h⁻¹ g_cat⁻¹) under model conditions (only [...] Read more.

A conventional Pt/CeO₂/Al₂O₃ catalyst physically mixed with an ionic conductor (Mo- or Eu-doped ZrO₂) was tested at high space velocity (20,000 h⁻¹ and 80 L h⁻¹ g_cat⁻¹) under model conditions (only with CO and H₂O) and industrial conditions, with a realistic feed. The promoted system with the ionic conductor physically mixed showed better catalytic activity associated with better water dissociation and mobility, considered as a rate-determining step. The water activation was assessed by operando diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) studies under reaction conditions and the Mo-containing ionic conductor exhibited the presence of both dissociated (3724 cm⁻¹) and physisorbed (5239 cm⁻¹) water on the Eu-doped ZrO₂ solid solution, which supports the appearance of proton conductivity by Grotthuss mechanism. Moreover, the band at 3633 cm⁻¹ ascribed to hydrated Mo oxide, which increases with the temperature, explains the increase of catalytic activity when the physical mixture was used in a water gas shift (WGS) reaction. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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21 pages, 3129 KiB

Open AccessArticle

Bimetallic Pt-Co Catalysts for the Liquid-Phase WGS

by Alberto José Reynoso, Jose Luis Ayastuy, Unai Iriarte-Velasco and Miguel Ángel Gutiérrez-Ortiz

Catalysts 2020, 10(8), 830; https://doi.org/10.3390/catal10080830 - 24 Jul 2020

Cited by 5 | Viewed by 2744

Abstract

Bimetallic Pt-Co catalysts derived from cobalt aluminate spinel were investigated in the liquid-phase water–gas shift (WGS) reaction and CO hydrogenation. Liquid-phase WGS is a key reaction in the aqueous-phase reforming (APR) of polyols; thus, WGS activity is essential to formulate good APR catalysts. [...] Read more.

Bimetallic Pt-Co catalysts derived from cobalt aluminate spinel were investigated in the liquid-phase water–gas shift (WGS) reaction and CO hydrogenation. Liquid-phase WGS is a key reaction in the aqueous-phase reforming (APR) of polyols; thus, WGS activity is essential to formulate good APR catalysts. In this work, catalysts with different Pt/Co molar ratios were synthesized together with a reference Pt/alumina. All the synthesized catalysts were characterized by various techniques in order to gain knowledge on their structural and surface characteristics. WGS activity was tested with a feedstream of CO/H₂O = 1/15 (space-time of 76.8 kg_cat·s/mol_CO), isothermal operation at 260 °C and 50 bar, for 10 TOS. Bimetallic Pt-Co catalysts showed improved activity in liquid-phase WGS in comparison to bare Co or Pt catalysts, which was ascribed to the synergistic effect. Despite being subjected to an increased hydrogen concentration in the feedstream (H₂/CO between 0 and 12/3), these catalysts maintained a preferential selectivity towards WGS activity. In addition, the effect of temperature (220–260 °C) and pressure (25–50 bar) was investigated over a catalyst with 0.3Pt/CoAl. CO conversion and CO₂ yield were more sensitive to temperature, while a higher pressure favored methane production. The measured activation energy in the 220–260 °C temperature range was 51.5 kJ/mol. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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18 pages, 3508 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

FeCeO_x Supported Ni, Sn Catalysts for the High-Temperature Water–Gas Shift Reaction

by Devaiah Damma and Panagiotis G. Smirniotis

Catalysts 2020, 10(6), 639; https://doi.org/10.3390/catal10060639 - 08 Jun 2020

Cited by 8 | Viewed by 3093

Abstract

In this work, the effect of monometallic Ni or Sn and bimetallic NiSn deposition on the activity of FeCeO_x catalysts in high-temperature water–gas (HT-WGS) reactions was investigated. It was found that the HT-WGS performance of FeCeO_x has significantly improved after the [...] Read more.

In this work, the effect of monometallic Ni or Sn and bimetallic NiSn deposition on the activity of FeCeO_x catalysts in high-temperature water–gas (HT-WGS) reactions was investigated. It was found that the HT-WGS performance of FeCeO_x has significantly improved after the deposition of Sn together with Ni on it. Furthermore, the bimetallic NiSn/FeCeO_x catalyst showed higher activity compared to the monometallic Ni/FeCeO_x and Sn/FeCeO_x catalysts within the tested temperature range (450–600 °C). Although the Ni/FeCeO_x catalyst showed methanation activity at a temperature below 550 °C, the NiSn/FeCeO_x catalyst suppressed the methane formation to zero in the WGS. Besides, the NiSn/FeCeO_x catalyst exhibited an excellent time-on-stream stability without methanation reaction, even at a steam-to-CO ratio as low as 0.8. The combination of Ni and Sn supported on FeCeO_x led to a large lattice strain, the formation of NiSn alloy, and a strong synergistic effect between the bimetallic NiSn and FeCeO_x mixed oxide support interface. All these features are very important in achieving the best activity and stability of NiSn/FeCeO_x in the HT-WGS reaction. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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16 pages, 2478 KiB

Open AccessArticle

Cr-Free, Cu Promoted Fe Oxide-Based Catalysts for High-Temperature Water-Gas Shift (HT-WGS) Reaction

by Sagar Sourav and Israel E. Wachs

Catalysts 2020, 10(3), 305; https://doi.org/10.3390/catal10030305 - 06 Mar 2020

Cited by 13 | Viewed by 4948

Abstract

Ca, Ni, Co, and Ge promoters were examined as potential candidates to substitute for the current toxic Cr in Cu-promoted Fe oxide-based catalysts for the HT-WGS reaction. The Ca and Ni promoters were found to improve catalyst performance relative to promotion with Cr. [...] Read more.

Ca, Ni, Co, and Ge promoters were examined as potential candidates to substitute for the current toxic Cr in Cu-promoted Fe oxide-based catalysts for the HT-WGS reaction. The Ca and Ni promoters were found to improve catalyst performance relative to promotion with Cr. The HS-LEIS surface analysis data demonstrate that Ca and Ge tend to segregate on the surface, while Ni, Co, and Cr form solid solutions in the Fe₃O₄ bulk lattice. The corresponding number of catalytic active sites, redox, and WGS activity values of the catalysts were determined with CO-TPR, CO+H₂O-TPSR, and SS-WGS studies, respectively. The poorer HT-WGS performances of the Ge and Co promoters are related to the presence of surface Ge and Co that inhibits catalyst redox ability, with the Co also not stabilizing the surface area of the Fe₃O₄ support. The Ni promoter uniformly disperses the Cu nanoparticles on the catalyst surface and increases the number of FeO_x-Cu interfacial redox sites. The Ca promoter on the catalyst surface, however, enhances the activity of the FeO_x-Cu interfacial redox sites. The CO+H₂O TPSR results reveal that the redox ability of the active sites follows the SS-WGS performance of the catalysts and show the following trend: 3Cu8CaFe > 3Cu8NiFe ≥ 3Cu8CrFe > 3Cu8CoFe >> 3Cu8GeFe. Furthermore, all the catalysts followed a redox-type reaction mechanism for the HT-WGS reaction. Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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18 pages, 5351 KiB

Open AccessArticle

Promotional Effect of Gold on the WGS Activity of Alumina-Supported Copper-Manganese Mixed Oxides

by Tatyana Tabakova, Ivan Ivanov, Yordanka Karakirova, Daniela Karashanova, Anna Maria Venezia, Petya Petrova, Georgi Avdeev, Elitsa Kolentsova and Krasimir Ivanov

Catalysts 2018, 8(11), 563; https://doi.org/10.3390/catal8110563 - 20 Nov 2018

Cited by 10 | Viewed by 3304

Abstract

The water-gas shift (WGS) reaction is a well-known industrial process used for the production of hydrogen. During the last few decades, it has attracted renewed attention due to the need for high-purity hydrogen for fuel-cell processing systems. The aim of the present study [...] Read more.

The water-gas shift (WGS) reaction is a well-known industrial process used for the production of hydrogen. During the last few decades, it has attracted renewed attention due to the need for high-purity hydrogen for fuel-cell processing systems. The aim of the present study was to develop a cost-effective and catalytically efficient formulation that combined the advantageous properties of transition metal oxides and gold nanoparticles. Alumina-supported copper- manganese mixed oxides were prepared by wet impregnation. The deposition-precipitation method was used for the synthesis of gold catalysts. The effect of the Cu:Mn molar ratio and the role of Au addition on the WGS reaction’s performance was evaluated. Considerable emphasis was put on the characterization of the as-prepared and WGS-tested samples by means of a number of physicochemical methods (X-ray powder diffraction, high-resolution transmission electron microscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and temperature-programmed reduction) in order to explain the relationship between the structure and the reductive and WGS behavior. Catalytic tests revealed the promotional effect of gold addition. The best performance of the gold-promoted sample with a higher Cu content, i.e., a Cu:Mn molar ratio of 2:1 might be related to the beneficial role of Au on the spinel decomposition and the highly dispersed copper particle formation during the reaction, thus, ensuring the presence of two highly dispersed active metallic phases. High-surface-area alumina that was modified with a surface fraction of Cu–Mn mixed oxides favored the stabilization of finely dispersed gold particles. These new catalytic systems are very promising for practical applications due to their economic viability because the composition mainly includes alumina (80%). Full article

(This article belongs to the Special Issue Catalysts for Water-Gas Shift Reaction)

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