Special Issue "Surface Chemistry and Catalysis"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (30 November 2015)

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Guest Editor
Dr. Michalis Konsolakis

School of Production Engineering & Management, Chania, GR-73100, Crete, Greece
Website | E-Mail
Phone: +30 28210 37682
Interests: heterogeneous catalysis; surface science; materials science and electro-catalysis with particular emphasis on structure-activity relationships

Special Issue Information

Dear Colleagues,

Heterogeneous catalysis plays a prominent role in our society. The majority of industrial chemical processes, involving the manufacturing of commodity chemicals, pharmaceuticals, clean fuels, etc., as well as the pollution abatement technologies have a common catalytic origin. As catalysis proceeds at the surface, it is of paramount importance to gain insight into the fundamental understanding of local surface chemistry, which in turn governs the catalytic performance.

Thanks to the surface science approach, we can obtain a profound insight into the structure of a surface, the chemical state of active sites, the interfacial reactivity, the way molecules bind and react, the role of surface defects and imperfections (e.g., surface oxygen vacancies), and the mode of action of various surface promoters/poisons. Τo elucidate the aforementioned surface phenomena, sophisticated techniques are necessary to reveal the composition and the structure/morphology of the surface, as well as the chemical entity of adsorbed species. Moreover, time-resolved methods are required to investigate the dynamic phenomena occurring at the surface, such as adsorption/desorption, diffusion and chemical reactions. The deep understanding at atomic level of catalyst surface could pave the way towards the design of novel catalytic systems for real-life energy and environmental applications

The present Special Issue is mainly focused on the recent developments in relation to catalyst surface that can be obtained by means of advanced characterization techniques (both ex situ and in situ), computational calculations (e.g., DFT method) and time-resolved methods. Studies in both model and conventional catalysts, with particular emphasis into the structure-activity relationships (SARs), are especially welcomed.

Dr. Michalis Konsolakis
Guest Editor

Keywords

  • heterogeneous catalysis
  • catalyst characterization
  • surface analysis
  • structure-activity correlation
  • spectroscopic studies
  • surface reactions
  • time-resolved analysis
  • operando studies
  • tailoring surface reactivity
  • computational studies

Published Papers (15 papers)

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Editorial

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Open AccessEditorial Surface Chemistry and Catalysis
Catalysts 2016, 6(7), 102; doi:10.3390/catal6070102
Received: 11 July 2016 / Revised: 12 July 2016 / Accepted: 12 July 2016 / Published: 15 July 2016
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Abstract
Nowadays, heterogeneous catalysis plays a prominent role.[...] Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available

Research

Jump to: Editorial, Review

Open AccessFeature PaperArticle Influence of Cobalt Precursor on Efficient Production of Commercial Fuels over FTS Co/SiC Catalyst
Catalysts 2016, 6(7), 98; doi:10.3390/catal6070098
Received: 30 November 2015 / Revised: 6 June 2016 / Accepted: 28 June 2016 / Published: 7 July 2016
Cited by 3 | PDF Full-text (5642 KB) | HTML Full-text | XML Full-text
Abstract
β-SiC-supported cobalt catalysts have been prepared from nitrate, acetate, chloride and citrate salts to study the dependence of Fischer–Tropsch synthesis (FTS) on the type of precursor. Com/SiC catalysts were synthetized by vacuum-assisted impregnation while N2 adsorption/desorption, XRD, TEM, TPR, O
[...] Read more.
β-SiC-supported cobalt catalysts have been prepared from nitrate, acetate, chloride and citrate salts to study the dependence of Fischer–Tropsch synthesis (FTS) on the type of precursor. Com/SiC catalysts were synthetized by vacuum-assisted impregnation while N2 adsorption/desorption, XRD, TEM, TPR, O2 pulses and acid/base titrations were used as characterization techniques. FTS catalytic performance was carried out at 220 °C and 250 °C while keeping constant the pressure (20 bar), space velocity (6000 Ncm3/g·h) and syngas composition (H2/CO:2). The nature of cobalt precursor was found to influence basic behavior, extent of reduction and metallic particle size. For β-SiC-supported catalysts, the use of cobalt nitrate resulted in big Co crystallites, an enhanced degree of reduction and higher basicity compared to acetate, chloride and citrate-based catalysts. Consequently, cobalt nitrate provided a better activity and selectivity to C5+ (less than 10% methane was formed), which was centered in kerosene-diesel fraction (α = 0.90). On the contrary, catalyst from cobalt citrate, characterized by the highest viscosity and acidity values, presented a highly dispersed distribution of Co nanoparticles leading to a lower reducibility. Therefore, a lower FTS activity was obtained and chain growth probability was shortened as observed from methane and gasoline-kerosene (α = 0.76) production when using cobalt citrate. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
Open AccessFeature PaperArticle Hydrogen Production by Ethanol Steam Reforming (ESR) over CeO2 Supported Transition Metal (Fe, Co, Ni, Cu) Catalysts: Insight into the Structure-Activity Relationship
Catalysts 2016, 6(3), 39; doi:10.3390/catal6030039
Received: 30 November 2015 / Revised: 18 February 2016 / Accepted: 2 March 2016 / Published: 8 March 2016
Cited by 17 | PDF Full-text (4864 KB) | HTML Full-text | XML Full-text
Abstract
The aim of the present work was to investigate steam reforming of ethanol with regard to H2 production over transition metal catalysts supported on CeO2. Various parameters concerning the effect of temperature (400–800 °C), steam-to-carbon (S/C) feed ratio (0.5, 1.5,
[...] Read more.
The aim of the present work was to investigate steam reforming of ethanol with regard to H2 production over transition metal catalysts supported on CeO2. Various parameters concerning the effect of temperature (400–800 °C), steam-to-carbon (S/C) feed ratio (0.5, 1.5, 3, 6), metal entity (Fe, Co, Ni, Cu) and metal loading (15–30 wt.%) on the catalytic performance, were thoroughly studied. The optimal performance was obtained for the 20 wt.% Co/CeO2 catalyst, achieving a H2 yield of up to 66% at 400 °C. In addition, the Co/CeO2 catalyst demonstrated excellent stability performance in the whole examined temperature range of 400–800 °C. In contrast, a notable stability degradation, especially at low temperatures, was observed for Ni-, Cu-, and Fe-based catalysts, ascribed mainly to carbon deposition. An extensive characterization study, involving N2 adsorption-desorption (BET), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM/EDS), X-ray Photoelectron Spectroscopy (XPS), and Temperature Programmed Reduction (H2-TPR) was undertaken to gain insight into the structure-activity correlation. The excellent reforming performance of Co/CeO2 catalysts could be attributed to their intrinsic reactivity towards ethanol reforming in combination to their high surface oxygen concentration, which hinders the deposition of carbonaceous species. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Gold-Iron Oxide Catalyst for CO Oxidation: Effect of Support Structure
Catalysts 2016, 6(3), 37; doi:10.3390/catal6030037
Received: 26 November 2015 / Revised: 11 January 2016 / Accepted: 26 January 2016 / Published: 7 March 2016
Cited by 5 | PDF Full-text (5691 KB) | HTML Full-text | XML Full-text
Abstract
Gold-iron oxide (Au/FeOx) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated
[...] Read more.
Gold-iron oxide (Au/FeOx) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O), have been used for the deposition of gold via a deposition-precipitation (DP) method. The structure of iron oxide has been tuned by either selecting precipitated pH of 6.7–11.2 for Fe_OH or changing calcination temperature of from 200 to 600 °C for Fe_O. Then, 1 wt. % Au catalysts on these iron oxide supports were measured for low-temperature CO oxidation reaction. Both fresh and used samples have been characterized by multiple techniques including transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and temperature-programmed reduction by hydrogen (H2-TPR). It has been demonstrated that the surface properties of the iron oxide support, as well as the metal-support interaction, plays crucial roles on the performance of Au/FeOx catalysts in CO oxidation. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
Open AccessFeature PaperArticle Study of N2O Formation over Rh- and Pt-Based LNT Catalysts
Catalysts 2016, 6(3), 36; doi:10.3390/catal6030036
Received: 11 January 2016 / Accepted: 17 February 2016 / Published: 1 March 2016
Cited by 7 | PDF Full-text (4513 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, mechanistic aspects involved in the formation of N2O over Pt-BaO/Al2O3 and Rh-BaO/Al2O3 model NOx Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by
[...] Read more.
In this paper, mechanistic aspects involved in the formation of N2O over Pt-BaO/Al2O3 and Rh-BaO/Al2O3 model NOx Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by using H2 and NH3 as reductants. It was found that N2O formation involves the presence of gas-phase NO, since no N2O is observed upon the reduction of nitrates stored over both Pt- and Rh-BaO/Al2O3 catalyst samples. In particular, N2O formation involves the coupling of undissociated NO molecules with N-adspecies formed upon NO dissociation onto reduced Platinum-Group-Metal (PGM) sites. Accordingly, N2O formation is observed at low temperatures, when PGM sites start to be reduced, and disappears at high temperatures where PGM sites are fully reduced and complete NO dissociation takes place. Besides, N2O formation is observed at lower temperatures with H2 than with NH3 in view of the higher reactivity of hydrogen in the reduction of the PGM sites and onto Pt-containing catalyst due to the higher reducibility of Pt vs. Rh. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Charge Transfer Mechanism in Titanium-Doped Microporous Silica for Photocatalytic Water-Splitting Applications
Catalysts 2016, 6(3), 34; doi:10.3390/catal6030034
Received: 30 November 2015 / Revised: 4 February 2016 / Accepted: 16 February 2016 / Published: 29 February 2016
Cited by 5 | PDF Full-text (4945 KB) | HTML Full-text | XML Full-text
Abstract
Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress,
[...] Read more.
Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti4+ ions embedded on the inner pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. This provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Methanol Reforming over Cobalt Catalysts Prepared from Fumarate Precursors: TPD Investigation
Catalysts 2016, 6(3), 33; doi:10.3390/catal6030033
Received: 30 November 2015 / Revised: 2 February 2016 / Accepted: 16 February 2016 / Published: 24 February 2016
Cited by 1 | PDF Full-text (3047 KB) | HTML Full-text | XML Full-text
Abstract
Temperature-programmed desorption (TPD) was employed to investigate adsorption characteristics of CH3OH, H2O, H2, CO2 and CO on cobalt-manganese oxide catalysts prepared through mixed Co-Mn fumarate precursors either by pyrolysis or oxidation and oxidation/reduction pretreatment. Pyrolysis temperature
[...] Read more.
Temperature-programmed desorption (TPD) was employed to investigate adsorption characteristics of CH3OH, H2O, H2, CO2 and CO on cobalt-manganese oxide catalysts prepared through mixed Co-Mn fumarate precursors either by pyrolysis or oxidation and oxidation/reduction pretreatment. Pyrolysis temperature and Co/Mn ratio were the variable synthesis parameters. Adsorption of methanol, water and CO2 was carried out at room temperature. Adsorption of H2 and H2O was carried out at 25 and 300 °C. Adsorption of CO was carried out at 25 and 150 °C. The goal of the work was to gain insight on the observed differences in the performance of the aforementioned catalysts in methanol steam reforming. TPD results indicated that activity differences are mostly related to variation in the number density of active sites, which are able to adsorb and decompose methanol. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle First-Principles Modeling of Direct versus Oxygen-Assisted Water Dissociation on Fe(100) Surfaces
Catalysts 2016, 6(2), 29; doi:10.3390/catal6020029
Received: 5 November 2015 / Revised: 4 February 2016 / Accepted: 15 February 2016 / Published: 18 February 2016
Cited by 2 | PDF Full-text (1567 KB) | HTML Full-text | XML Full-text
Abstract
The O–H bond breaking in H2O molecules on metal surfaces covered with pre-adsorbed oxygen atoms is an important topic in heterogeneous catalysis. The adsorption configurations of H2O and relevant dissociation species on clean and O-pre-adsorbed Fe(100) surfaces were investigated
[...] Read more.
The O–H bond breaking in H2O molecules on metal surfaces covered with pre-adsorbed oxygen atoms is an important topic in heterogeneous catalysis. The adsorption configurations of H2O and relevant dissociation species on clean and O-pre-adsorbed Fe(100) surfaces were investigated by density functional theory (DFT). The preferential sites for H2O, HO, O, and H were investigated on both surfaces. Both the first H abstraction from adsorbed H2O and the subsequent OH dissociation are exothermic on the O-pre-adsorbed Fe(100) surface. However, the pre-adsorbed O significantly reduces the kinetics energy barriers for both reactions. Our results confirmed that the presence of pre-adsorbed oxygen species could significantly promote H2O dissociation. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
Open AccessArticle Aerobic Catalytic Oxidation of Cyclohexene over TiZrCo Catalysts
Catalysts 2016, 6(2), 24; doi:10.3390/catal6020024
Received: 8 December 2015 / Revised: 7 January 2016 / Accepted: 12 January 2016 / Published: 29 January 2016
Cited by 3 | PDF Full-text (1637 KB) | HTML Full-text | XML Full-text
Abstract
The aerobic oxidation of hydrocarbon is of great significance from the viewpoints of both fundamental and industry studies as it can transfer the petrochemical feedstock into valuable chemicals. In this work, we investigated the aerobic oxidation of cyclohexene over TiZrCo catalysts, in which
[...] Read more.
The aerobic oxidation of hydrocarbon is of great significance from the viewpoints of both fundamental and industry studies as it can transfer the petrochemical feedstock into valuable chemicals. In this work, we investigated the aerobic oxidation of cyclohexene over TiZrCo catalysts, in which 2-cyclohexen-1-one was produced with a high selectivity of 57.6% at a conversion of 92.2%, which are comparable to the best results reported for the aerobic oxidation of cyclohexene over heterogeneous catalysts. The influences of kinds of solvent, substrate concentration and reaction temperature were evaluated. Moreover, the catalytic performance of the TiZrCo catalyst and the main catalytic active species were also discussed. The results of SEM, XRD and XPS suggested that the surface CoO and Co3O4 species are the catalytic active species and contribute to the high activity and selectivity in the present cyclohexene oxidation. The present catalytic system should have wide applications in the aerobic oxidation of hydrocarbons. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Competition of CO and H2 for Active Oxygen Species during the Preferential CO Oxidation (PROX) on Au/TiO2 Catalysts
Catalysts 2016, 6(2), 21; doi:10.3390/catal6020021
Received: 14 December 2015 / Revised: 15 January 2016 / Accepted: 19 January 2016 / Published: 27 January 2016
Cited by 5 | PDF Full-text (657 KB) | HTML Full-text | XML Full-text
Abstract
Aiming at an improved mechanistic understanding of the preferential oxidation of CO on supported Au catalysts, we have investigated the competition between CO and H2 for stable, active oxygen (Oact) species on a Au/TiO2 catalyst during the simultaneous exposure
[...] Read more.
Aiming at an improved mechanistic understanding of the preferential oxidation of CO on supported Au catalysts, we have investigated the competition between CO and H2 for stable, active oxygen (Oact) species on a Au/TiO2 catalyst during the simultaneous exposure to CO and H2 with various CO/H2 ratios at 80 °C and 400 °C by quantitative temporal analysis of products (TAP) reactor measurements. It is demonstrated that, at both higher and lower temperature, the maximum amount of active oxygen removal is (i) independent of the CO/H2 ratio and (ii) identical to the amount of active oxygen removal by CO or H2 alone. Hence, under preferential CO oxidation (PROX) reaction conditions, in the simultaneous presence of CO and H2, CO and H2 compete for the same active oxygen species. In addition, also the dependency of the selectivity towards CO oxidation on the CO/H2 ratio was evaluated from these measurements. Consequences of these findings on the mechanistic understanding of the PROX reaction on Au/TiO2 will be discussed. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
Open AccessArticle Ni Catalysts Supported on Modified Alumina for Diesel Steam Reforming
Catalysts 2016, 6(1), 11; doi:10.3390/catal6010011
Received: 12 November 2015 / Revised: 18 December 2015 / Accepted: 7 January 2016 / Published: 13 January 2016
Cited by 5 | PDF Full-text (1536 KB) | HTML Full-text | XML Full-text
Abstract
Nickel catalysts are the most popular for steam reforming, however, they have a number of drawbacks, such as high propensity toward coke formation and intolerance to sulfur. In an effort to improve their behavior, a series of Ni-catalysts supported on pure and La-,
[...] Read more.
Nickel catalysts are the most popular for steam reforming, however, they have a number of drawbacks, such as high propensity toward coke formation and intolerance to sulfur. In an effort to improve their behavior, a series of Ni-catalysts supported on pure and La-, Ba-, (La+Ba)- and Ce-doped γ-alumina has been prepared. The doped supports and the catalysts have been extensively characterized. The catalysts performance was evaluated for steam reforming of n-hexadecane pure or doped with dibenzothiophene as surrogate for sulphur-free or commercial diesel, respectively. The undoped catalyst lost its activity after 1.5 h on stream. Doping of the support with La improved the initial catalyst activity. However, this catalyst was completely deactivated after 2 h on stream. Doping with Ba or La+Ba improved the stability of the catalysts. This improvement is attributed to the increase of the dispersion of the nickel phase, the decrease of the support acidity and the increase of Ni-phase reducibility. The best catalyst of the series doped with La+Ba proved to be sulphur tolerant and stable for more than 160 h on stream. Doping of the support with Ce also improved the catalytic performance of the corresponding catalyst, but more work is needed to explain this behavior. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Characterization and Catalytic Activity of Mn-Co/TiO2 Catalysts for NO Oxidation to NO2 at Low Temperature
Catalysts 2016, 6(1), 9; doi:10.3390/catal6010009
Received: 7 November 2015 / Revised: 27 December 2015 / Accepted: 5 January 2016 / Published: 11 January 2016
Cited by 8 | PDF Full-text (2019 KB) | HTML Full-text | XML Full-text
Abstract
A series of Mn-Co/TiO2 catalysts were prepared by wet impregnation method and evaluated for the oxidation of NO to NO2. The effects of Co amounts and calcination temperature on NO oxidation were investigated in detail. The catalytic oxidation ability in
[...] Read more.
A series of Mn-Co/TiO2 catalysts were prepared by wet impregnation method and evaluated for the oxidation of NO to NO2. The effects of Co amounts and calcination temperature on NO oxidation were investigated in detail. The catalytic oxidation ability in the temperature range of 403–473 K was obviously improved by doping cobalt into Mn/TiO2. These samples were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and hydrogen temperature programmed reduction (H2-TPR). The results indicated that the formation of dispersed Co3O4·CoMnO3 mixed oxides through synergistic interaction between Mn-O and Co-O was directly responsible for the enhanced activities towards NO oxidation at low temperatures. Doping of Co enhanced Mn4+ formation and increased chemical adsorbed oxygen amounts, which also accelerated NO oxidation. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Phosphotungstate-Based Ionic Silica Nanoparticles Network for Alkenes Epoxidation
Catalysts 2016, 6(1), 2; doi:10.3390/catal6010002
Received: 28 October 2015 / Revised: 13 December 2015 / Accepted: 14 December 2015 / Published: 24 December 2015
Cited by 1 | PDF Full-text (2268 KB) | HTML Full-text | XML Full-text
Abstract
An inorganic-organic porous silica network catalyst was prepared by linking silica nanoparticles using ionic liquid and followed by anion-exchange with phosphotungstate. Characterization methods of FT-IR, TG, SEM, TEM, BET, etc., were carried out to have a comprehensive insight into the catalyst. The
[...] Read more.
An inorganic-organic porous silica network catalyst was prepared by linking silica nanoparticles using ionic liquid and followed by anion-exchange with phosphotungstate. Characterization methods of FT-IR, TG, SEM, TEM, BET, etc., were carried out to have a comprehensive insight into the catalyst. The catalyst was used for catalyzing cyclooctene epoxidation with high surface area, high catalytic activity, and convenient recovery. The conversion and selectivity of epoxy-cyclooctene could both reach over 99% at 70 °C for 8 h using hydrogen peroxide (H2O2) as an oxidant, and acetonitrile as a solvent when the catalyst was 10 wt. % of cyclooctene. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Open AccessArticle Synthesis of Ethanol from Syngas over Rh/MCM-41 Catalyst: Effect of Water on Product Selectivity
Catalysts 2015, 5(4), 1737-1755; doi:10.3390/catal5041737
Received: 20 August 2015 / Revised: 24 September 2015 / Accepted: 10 October 2015 / Published: 19 October 2015
Cited by 5 | PDF Full-text (720 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The thermochemical processing of biomass is an alternative route for the manufacture of fuel-grade ethanol, in which the catalytic conversion of syngas to ethanol is a key step. The search for novel catalyst formulations, active sites and types of support is of current
[...] Read more.
The thermochemical processing of biomass is an alternative route for the manufacture of fuel-grade ethanol, in which the catalytic conversion of syngas to ethanol is a key step. The search for novel catalyst formulations, active sites and types of support is of current interest. In this work, the catalytic performance of an Rh/MCM-41 catalyst has been evaluated and compared with a typical Rh/SiO2 catalyst. They have been compared at identical reaction conditions (280 °C and 20 bar), at low syngas conversion (2.8%) and at same metal dispersion (H/Rh = 22%). Under these conditions, the catalysts showed different product selectivities. The differences have been attributed to the concentration of water vapor in the pores of Rh/MCM-41. The concentration of water vapor could promote the water-gas-shift-reaction generating some extra carbon dioxide and hydrogen, which in turn can induce side reactions and change the product selectivity. The extra hydrogen generated could facilitate the hydrogenation of a C2-oxygenated intermediate to ethanol, thus resulting in a higher ethanol selectivity over the Rh/MCM-41 catalyst as compared to the typical Rh/SiO2 catalyst; 24% and 8%, respectively. The catalysts have been characterized, before and after reaction, by N2-physisorption, X-ray photoelectron spectroscopy, X-ray diffraction, H2-chemisorption, transmission electron microscopy and temperature programmed reduction. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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Review

Jump to: Editorial, Research

Open AccessReview A Review of Surface Analysis Techniques for the Investigation of the Phenomenon of Electrochemical Promotion of Catalysis with Alkaline Ionic Conductors
Catalysts 2016, 6(1), 15; doi:10.3390/catal6010015
Received: 30 November 2015 / Revised: 6 January 2016 / Accepted: 6 January 2016 / Published: 18 January 2016
Cited by 4 | PDF Full-text (1755 KB) | HTML Full-text | XML Full-text
Abstract
Electrochemical Promotion of Catalysis (EPOC) with alkali ionic conductors has been widely studied in literature due to its operational advantages vs. alkali classical promotion. This phenomenon allows to electrochemically control the alkali promoter coverage on a catalyst surface in the course of
[...] Read more.
Electrochemical Promotion of Catalysis (EPOC) with alkali ionic conductors has been widely studied in literature due to its operational advantages vs. alkali classical promotion. This phenomenon allows to electrochemically control the alkali promoter coverage on a catalyst surface in the course of the catalytic reaction. Along the study of this phenomenon, a large variety of in situ and ex situ surface analysis techniques have been used to investigate the origin and mechanism of this kind of promotion. In this review, we analyze the most important contributions made on this field which have clearly evidenced the presence of adsorbed alkali surface species on the catalyst films deposited on alkaline solid electrolyte materials during EPOC experiments. Hence, the use of different surface analysis techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), or scanning tunneling microscopy (STM), led to a better understanding of the alkali promoting effect, and served to confirm the theory of electrochemical promotion on this kind of catalytic systems. Given the functional similarities between alkali electrochemical and chemical promotion, this review aims to bring closer this phenomenon to the catalysis scientific community. Full article
(This article belongs to the Special Issue Surface Chemistry and Catalysis) Printed Edition available
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