Operando FTIR Research Articles

A Hybrid Ru(II)/TiO2 Catalyst for Steadfast Photocatalytic CO2 to CO/Formate Conversion Following a Molecular Catalytic Route

Herein, we employed a molecular Ru(II) catalyst immobilized onto TiO2 particulates of (4,4'-Y2-bpy)RuII(CO)2Cl2 (RuP; Y = CH2PO(OH)2), as a hybrid catalyst system to secure the efficient and steady catalytic activity of a molecular bipyridyl Ru(II)-complex-based photocatalytic system for CO2 reduction. From a series of operando FTIR spectrochemical analyses, it was found that the TiO2-fixed molecular Ru(II) complex leads to efficient stabilization of the key monomeric intermediate, RuII-hydride (LRuII(H)(CO)2Cl), and suppresses the formation of polymeric Ru(II) complex (-(L(CO)2Ru-Ru(CO)2L)n-), which is a major deactivation product produced during photoreaction via the Ru-Ru dimeric route. Active promotion of the monomeric catalytic route in a hetero-binary system (IrPS + TiO2/RuP) that uses TiO2-bound Ru(II) complex as reduction catalyst led to highly increased activity as well as durability of photocatalytic behavior with respect to the homogeneous catalysis of free Ru(II) catalyst (IrPS + Ru(II) catalyst). This catalytic strategy produced maximal turnover numbers (TONs) of >4816 and >2228, respectively, for CO and HCOO- production in CO2-saturated N,N-dimethylformamide (DMF)/TEOA (16.7 vol % TEOA) solution containing a 0.1 M sacrificial electron donor.

A simultaneous operando FTIR & Raman study of propane ODH mechanism over V-Zr-O catalysts

Simultaneous operando Raman and transmission FTIR spectroscopic measurements have been combined for the study of the structure-activity relationships of V-Zr-O catalysts during propane oxidative dehydrogenation (ODH). The combination of both spectroscopies during reaction allows the identification of reaction intermediates and yields structural information about the catalyst. The experimental results are compared with available data in the literature to propose a reaction mechanism for propane ODH on V-Zr-O catalytic systems, and to identify the role of different oxygen species bound to vanadium sites. The results are consistent with a Mars-van Krevelen mechanism. Besides, they clearly show higher activity of bridging oxygen sites (V-O-V, V-O-Zr) than terminal VO bonds.

Towards a greater olefin share in polypropylene cracking – Amorphous mesoporous aluminosilicate competes with zeolites

For plastic waste cracking the path for production of high olefins yield without loose in gasoline fraction is an intriguing option. Among the commercial FAU zeolites of different properties and mesoporous HAlMCM-48 materials, the catalysts of polypropylene (PP) cracking being able to operate in low-temperature regime was searched. The aim was to investigate the effects of the presence of mesopore system in the context of internal and external acidic features on PP cracking. The advanced operando FT-IR and UV–vis characterization coupled with GC and MS analysis offered insight into the nature of active species during cracking reaction as well as into the nature of coke deposit formed after reaction. The results for series of FAU zeolites were faced with mesoporous HAIMCM-48 as the catalyst of similar cracking competence, as it will be documented.

Enhancing the CO2 methanation activity of γ-Al2O3 supported mono- and bi-metallic catalysts prepared by glycerol assisted impregnation

Conventional Ni/Al2O3 catalyst, currently used for COx removal in ammonia production, admits room for improvement as catalysts for application in low temperature CO2 methanation, which is the aim of this work. The Incipient Wetness Impregnation (IWI) has been replaced by Glycerol Assisted Impregnation (GAI) method and, afterwards, a secondary metal (Ru) has been co-impregnated forming a bimetallic system. The monometallic as well as bimetallic systems have been characterized by several techniques (TGA, XRD, N2-physisorption, TEM, H2-TPR, H2-TPD, STEM-EDX and operando FTIR) and tested for CO2 methanation reaction in a downflow fixed bed reactor (conditions: P =1 bar, H2: CO2 ratio = 4 and WHSV = 30,000 mL h−1 g−1). GAI method together with a reducing calcination atmosphere (20 %H2/N2) results effective to avoid the formation of large metal particles during the synthesis, especially for Ru/Al2O3 formulation. In fact, the Ru dispersion of the catalyst prepared by GAI (RuAlGAI) is around 5 times higher than that of RuAlIWI catalyst. On the other hand, NiAlGAI presents larger population of reduced particles but bigger in size than NiAlIWI catalyst, which finally provides the former with slightly higher metal surface and superior catalytic performance. By co-impregnating small amounts of Ru (0.5, 1.0 or 1.5 wt%) the Ni surface is considerably increased which, together with Ru synergistic collaboration, results in a methane yield rise from 20 to 44 % at 300 °C. The operando FTIR results show no differences in the reaction pathway with GAI preparation method and incorporation of Ru, but different evolution of reaction intermediates concentration with temperature. The bimetallic Ni-RuAl system presents much higher capacity to adsorb CO and hydrogenate the reaction intermediates (adsorbed formates and carbonyls) by dissociated H2 than its monometallic counterparts.

HCl-doping of V/TiO2-based catalysts reveals the promotion of NH3-SCR and the rate limiting role of NO oxidative activation

NH3-SCR is the best available technology for NOx abatement from power plant, incinerators, gasifiers, and a well-established technology for on board NOx emission control; in the last 40 years, the reaction mechanism and kinetics have been deeply investigated, but the understanding of the nature of surface intermediates and rate determining steps is still object of a lively discussion. A major factor, though, has been largely neglected in the scientific literature, that is the presence of HCl in the flue gases generated by coal, biomass and plastics. In this work, the effect of HCl on NH3-SCR over V2O5 catalysts was investigated through combined kinetic analysis and operando FTIR. Unexpectedly, after HCl-doping, the catalyst intrinsic activity of a commercial catalyst increased by a factor of 5. Besides, it was found that while the NH3 surface coverage is little affected by HCl-doping, the chemisorption capacity of NO + O2 undergoes a remarkable promotion that scales with the promotion of the reaction rate. The HCl-effect provided thus an indirect but unambiguous piece of evidence that NO-activation by an O-species is a key rate controlling step of NH3-SCR.

Electrochemistry of the Interaction of Methane with Platinum at Room Temperature Investigated through Operando FTIR Spectroscopy and Voltammetry

Electrochemical processes show potential to enable new catalytic technologies that facilitate the conversion of light alkanes in more mild conditions than those traditionally employed in thermochem...

Decoupling the effect of Ni particle size and surface oxygen deficiencies in CO2 methanation over ceria supported Ni

The study describes decoupling the effect of surface oxygen vacancies and Ni particle size in the CO2 methanation over CeO2 supported Ni nanoparticles. The availability of surface oxygen vacancies with the interaction between Ni and CeO2 served to appreciably enhance the catalytic capacity for activation of CO2, generating higher conversion rates, larger selectivity to CH4 and lower activation energies relative to Ni/SiO2. A structure-sensitivity in the reaction over Ni/CeO2 was established without the interference of different concentrations of surface oxygen vacancies, where the turnover frequencies of CO2 decreased with increasing the Ni nanoparticle sizes (8−21 nm). The TPSR and Operando FT-IR analysis demonstrated that formate was the critical intermediate for CH4 formation. The CO formation with smaller nickel size resulted from the carboxyl species. In addition, the long-term evaluations and TGA measurements revealed small Ni nanoparticles suffered a temporary loss of activity due to the carbon deposition.

Operando Investigation of Toluene Oxidation over 1D Pt@CeO2 Derived from Pt Cluster-Containing MOF.

A unique 1D nanostructure of Pt@CeO2-BDC was prepared from Pt@CeBDC MOF. The Pt@CeO2-BDC was rich in oxygen vacancies (i.e., XPS Oβ/(Oα + Oβ) = 39.4%), and on the catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D mesoporous polycrystalline CeO2. Toluene oxidation was conducted in a spectroscopic operando Raman-online FTIR reactor to elucidate the reaction mechanism and establish the structure-activity relationship. The reaction proceeds as follows: (I) adsorption of toluene as benzoate intermediates on Pt@CeO2-BDC at low temperature by reaction with surface peroxide species; (II) reaction activation and ring-opening involving lattice oxygen with a concomitant change in defect densities indicative of surface rearrangement; (III) complete oxidation to CO2 and H2O by lattice oxygen and reoxidation of the reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt2+ with minor amounts of Pt0 and Pt4+ on the surface, facilitated the adsorption and reaction activation. The Pt-CeO2 interface generates reduced ceria sites forming nearby adsorbed peroxide at low temperature that oxidize toluene into benzoate species by a Langmuir-Hinshelwood mechanism. As the reaction temperature increases, the role of lattice oxygen becomes important, producing CO2 and H2O mainly by the Mars-van Krevelen mechanism.

A highly selective FER-based catalyst to produce n-butenes from isobutanol

The conversion of isobutanol to light olefins over zeolites was investigated by IR operando spectroscopy. FER zeolites showed a surprisingly high selectivity for the direct conversion of iso-butanol to linear butenes, hence catalyzing dehydration and skeletal isomerization in one step. As a fundamental understanding of the separate reactions is required to design superior catalysts, an in-situ and operando FT-IR mechanistic study of the reaction was carried out. The spectroscopic data, the derived species participating and their respective role are analyzed using chemometric (PCA and MCR-ALS) tools. We highlighted the role played by the external acid sites and the requirement of a specific distance between these sites to ensure the n-butene selectivity and point that the internal Brønsted acidity has an adverse effect on the catalyst stability. Moreover, there is no correlation between the carbon species formed on the surface and the exceptional selectivity towards n-butenes, allowing to exclude a “carbon pool” mechanism.

Oxygen Reduction Pathways in the Li-O2 Battery: Understanding Solvent-Water Interactions

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the capacity of Li-ion batteries. We must explore alternatives to Li-ion if we are to have any hope of meeting the long-term requirements for energy storage. One such alternative technology is the Li-air (O2) battery; its theoretical specific energy exceeds that of Li-ion five-fold, but many obstacles face its realisation.1–4 It is assumed that H2O in the Li-O2 battery will result in irreversible formation of LiOH and thus gas streams must be dried before entering the battery. Projections have suggested that this would sacrifice one third of the pack weight to a gas filtration unit required to bring atmospheric H2O content to functional levels (<1 ppm).5–9 Understanding the specific solvent properties that are associated with H2O tolerance, or distinct lack of, can guide rational selection of solvents able to tolerate wet air streams and reduce the requirements of the gas filtration unit, increasing the practical energy density.Here we consider competition between reversible 2e- O2 reduction and proton coupled irreversible 4e- O2 reduction. The predisposition to favour one of these O2 reduction pathways is largely solvent dependent. We have combined a range of methods including cyclic voltammetry, operando pressure analysis, NMR, FTIR, Raman, UV-vis spectroscopy and SEM to investigate the O2 reduction pathways in four common Li-air electrolytes containing H2O.10 H2O concentrations spanning 0–36% were employed to understand the onset and of the irreversible 4e- O2 reduction process across these solvents, with specific solvent properties being attributed to their performance. The results of these studies will be presented, along with their implications on rational future solvent development for rechargeable Li-O2 battery electrolytes. Reference s : [1] X. Gao, Y. Chen, L. Johnson and P. G. Bruce, Nat. Mater. 15 (2016) 882–888.[2] N. Feng, P. He and H. Zhou, Adv. Energy Mater. 6 (2016) 1502303.[3] L. Ma, T. Yu, E. Tzoganakis, K. Amine, T. Wu, Z. Chen and J. Lu, Adv. Energy Mater. 8 (2018) 1–13.[4] D. Aurbach, B. D. McCloskey, L. F. Nazar and P. G. Bruce, Nat. Energy 1 (2016) 16128.[5] K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu and V. Srinivasan, Energy Environ. Sci. 7 (2014) 1555-1563.[6] P. Tan, W. Shyy, T. S. Zhao, R. H. Zhang and X. B. Zhu, Appl. Energy 182 (2016) 569–575.[7] C. Shu, J. Wang, J. Long, H. K. Liu and S. X. Dou, Adv. Mater. 31 (2019) 1–43.[8] A. Dai, Q. Li, T. Liu, K. Amine and J. Lu, Adv. Mater. 31 (2018) 1805602.[9] D. G. Kwabi, T. P. Batcho, S. Feng, L. Giordano, C. V. Thompson and Y. Shao-Horn, Phys. Chem. Chem. Phys., 18 (2016) 24944–24953.[10] H. Guo, W. Luo, J. Chen, S. Chou, H. Liu and J. Wang, Adv. Sustain. Syst. 2 (2018) 1700183.

Unique design of superior metal-organic framework for removal of toxic chemicals in humid environment via direct functionalization of the metal nodes

Unique chemical and thermal stabilities of a zirconium-based metal-organic framework (MOF) and its functionalized analogues play a key role to efficiently remove chemical warfare agents (ex., cyanogen chloride, CNCl) and simulant (dimethyl methylphosphonate, DMMP) as well as industrial toxic gas, ammonia (NH3). Herein, we for the first time demonstrate outstanding performance of MOF-808 for removal of toxic chemicals in humid environment via special design of functionalization of hydroxo species bridging Zr-nodes using a triethylenediamine (TEDA) to form ionic frameworks by gas phase acid-base reactions. In situ experimental analyses and first-principles density functional theory calculations unveil underlying mechanism on the selective deposition of TEDA on the Zr-bridging hydroxo sites (μ3-OH) in Zr-MOFs. The crystal structure of TEDA-grafted MOF-808 was confirmed using synchrotron X-ray powder diffraction (SXRPD). Furthermore, operando FT-IR spectra elucidate why the TEDA-grafted MOF-808 shows by far superior sorption efficiency to other MOF varieties. This work provides design principles and applications how to optimize MOFs for the preparation for versatile adsorbents using diamine grafting chemistry, which is also potentially applicable to various catalysis.

Pd-modified beta zeolite for modulated hydro-cracking of low-density polyethylene into a paraffinic-rich hydrocarbon fuel

The catalytic properties of a microporous beta zeolite and Pd-loaded analogue were assessed in the cracking of low-density polyethylene (LDPE). The idea behind this study was to investigate the potential of zeolite beta from a different perspective, aiming at producing a hydrocarbon fuel, i.e. formed by saturated hydrocarbons, without the addition of external H2 but using the self-generated hydrogen, or hydrogen-transfer reactions. For this, a catalytic system was carefully prepared and compared to the bare beta zeolite; a protonic Pd-containing beta zeolite has a similar texture, structure and acidity features as in the base zeolite. The characterisation showed that this catalyst was achieved. The operando FTIR catalytic results indicated that the Pd-beta zeolite reaches a high selectivity towards the C2-C5 and aromatics fractions, with better control of the composition of the C2-C5 fraction leading to high isoparaffinic content, and a relatively low share of olefinic compounds. Additionally, the retardation in the coke forming reactions was evidenced, due to the high Pd-hydrogenation efficiency. Further insights were rationalized about the coke content and the catalyst auto-regeneration. From the process point of view, it was found that the use of a beta zeolite having well-dispersed Pd is an effective way to upgrade the LDPE into a paraffinic-rich hydrocarbon fuel.

Operando Reactor-Cell with Simultaneous Transmission FTIR and Raman Characterization (IRRaman) for the Study of Gas-Phase Reactions with Solid Catalysts.

Raman and transmission FTIR spectroscopic techniques have been coupled in a new homemade reactor-cell designed in a joint CSIC-LCS collaboration. The setup is easily adapted to any FTIR and fiber-coupled Raman spectrometers and gas analysis techniques. It allows for simultaneous operando FTIR and Raman spectroscopic measurement, which provide complementary characterization of adsorbed species, reaction intermediates, and structural properties of the catalyst. This system was validated with the study of vanadium-based catalysts during propane oxydehydrogenation (ODH). The combined use of both spectroscopies with gas analysis techniques to measure the activity contributes to the understanding of propane ODH and the identification of the role of different oxygen species bound to vanadium sites. For example, the simultaneous characterization of the catalyst under the same conditions by IR and Raman confirms that the V═O mode has the same frequency in both spectroscopies and that bridging oxygen sites (V-O-V, V-O-Zr) present higher activity than terminal V═O bonds. These results demonstrate the high potential of the new simultaneous transmission IR-Raman operando rig to correlate the activity and the structure of catalysts, thus assisting the rational design of catalytic processes.

Low-temperature Pd/FER NOx adsorbers: Operando FT-IR spectroscopy and performance analysis

A Pd-doped FER zeolite sample is synthesized and investigated for potential use in the low-temperature NOx adsorption. The catalyst is characterized by BET, XRD, TEM, NaCl titration and by in-situ FT-IR spectroscopy following adsorption of CO, NH3 and NO for the characterization of the Pd sites. Over the calcined sample, Pd is present mainly as PdOx clusters/particles; near 13 % of Pd is present in the form of isolated ions.The NOx adsorption / desorption performances at low temperature are investigated by microreactor studies and operando FT-IR upon NO/O2 adsorption followed by TPD under relevant operating conditions, i.e. in the presence of water and carbon dioxide. It is found that NO adsorbs in the form of Pd nitrosyls (hydrated and anhydrous) and nitrates; near 59 μmol/gcat of NOx could be adsorbed, corresponding to a NO/Pd ratio near 0.6. Upon heating, nitrosyls decompose and transform into anhydrous species leading to NO desorption in the low-T region (below 200 °C) and at higher temperature, with maximum near 370 °C. The presence of CO negatively affects the NOx storage capacity, due to a competition of CO and NO over the Pd storage sites.

Ultrafast time-resolved quantum cascade laser diagnostic for revealing the role of surface formate species in the photocatalytic oxidation of methanol

QCL-assisted operando FT-IR spectroscopy revealed the role of surface formate species in the photocatalytic oxidation of methanol over TiO2.

(Invited) Aqueous Thermal-Electrochemical Catalysis for Light Alkane Upgrading

The recent dramatic increase in supply of natural gas in the United States, largely enabled by rises in shale gas production, presents a unique opportunity to develop new catalytic processes that utilize abundant light alkanes for chemical manufacturing and transportation fuel synthesis. Alkenes as well as alcohols and other oxygenates are attractive target product molecules because they are either commodity chemicals or serve as precursors for production of commodity synthetic materials. This presentation will describe several approaches for designing new catalysts and reaction schemes for light alkane upgrading. These approaches include thermal catalytic, electrocatalytic, and hybrid thermal-electrocatalytic reactions in both batch and flow conditions. The presented work shows that oxidative functionalization of C-H bonds is possible using only air, water, and electricity as inputs when suitable catalysts and reaction conditions are utilized. Results demonstrate conversion of methane and ethane into a number of oxygenates and hydrocarbons at temperatures below 60 ºC in aqueous conditions, and quantify the associated catalytic performance. These efforts are supplemented by ex situ materials characterization and operando FTIR spectroscopy measurements, which provide new insights into the nature of these aqueous thermal and thermal-electrocatalytic reactions. The use of reactive oxidizing species generated from air and water for low temperature hydrocarbon catalysis has enormous potential to open new avenues of research. Additionally, the fundamental insights gained on the role of water in driving product selectivity in these reactions will be of interest to the broader catalysis community, which often encounter water in the gas phase as a side reactant.

Conversion of CO2 to C1 chemicals: Catalyst design, kinetics and mechanism aspects of the reactions

The conversion of carbon dioxide, an abundant and inexpensive feedstock to valuable chemicals is a contemporary challenge with multiple facets. There is a need to elucidate the process of utilizing CO2 to gain a fundamental understanding to overcome the challenges. This review focuses on the reactions converting CO2 to C1 valuable chemicals via reforming and hydrogenation reactions to produce syngas, methane, and methanol. Prior art and recent trends in the development of novel catalysts are highlighted with regards to kinetic and mechanistic aspects of the reactions. Several highly emerging characterization techniques such as operando XAS and FTIR and DFT simulation are used to study state of catalyst surface and reaction intermediates involved in the reactions. Furthermore, parameters affecting the selectivity towards desired products and methods to improve the performance are explained in greater details. The technical challenges of CO2 conversion into useful fuels/chemicals are summarized comprehensively. Finally, the future outlook and direction for the development of catalyst are provided to overcome the limitations and achieve higher utilization of CO2 to eradicate the problems associated with global warming.

Slowing down the deactivation of H-ZSM-5 zeolite catalyst in the methanol-to-olefin (MTO) reaction by P or Zn modifications

Abstract The benefits of H-ZSM-5 zeolite modification with H3PO4 or ZnCl2 have been analyzed during the methanol to olefins (MTO) reaction. The catalysts were prepared, characterized and tested using three different reactors: fixed-bed, operando FTIR and UV–vis. The spent catalysts were further characterized for analyzing the nature and location of the species trapped. The results show that the zeolite modified with H3PO4 has suffered a simultaneous dealumination, leading to a decrease of number of acid sites and activity. However, the zeolite modified with ZnCl2 shows the inclusion of Zn transforming Bronsted into Lewis acid sites, leading to reaction intermediates (hydrocarbon pool species) that decreases the rate of reaction but improves propylene selectivity (+10%), slows downs coke formation (-42%) and expands catalytic lifetime (+80%). The distinct effect of Zn modification, typically associated with the promotion of aromatics, is explained on the grounds of the severe transformation of the strong and Bronsted acid sites.

Photo-assisted SCR over highly dispersed silver sub-nanoparticles in zeolite under visible light: An Operando FTIR study

In this study, the photo-assisted SCR-NH3 activities of vanadium containing zeolite X (ZX-V) and Ag@ZX-V catalysts are investigated under visible-light and soft temperature conditions (RT and T = 150 °C). The highly dispersed silver was incorporated into the zeolite structure as Agnδ+ nano and sub-nano-clusters with small particle size using a new photochemical concept. The catalysts were characterized using different techniques such as XRD, N2 sorption, H-TEM, and DR–UV–Vis. An in situ FTIR study of adsorbed CO was also performed for the characterization of the metal sites and their accessibility. The catalytic reaction was investigated using the operando FTIR technique allowing the study of both Ag@ZX-V and ZX-V catalytic surfaces, and the gas phase of the reaction in real time. Both catalysts are not active in dark and only Ag@ZX-V exhibits a photocatalytic activity under visible light. At RT, the results show that silvers clusters promote the photocatalytic oxidation of NH3/NO, and no SCR is observed. This probably due to an energy transfer from the metallic site to the triplet oxygen and the formation of highly oxidant singlet oxygen. However, at T = 150 °C a significant photo-assisted SCR activity is observed under visible light irradiation with more than 18% of additional NOx removal. The different behavior of the material at 150 °C in respect to its activity at RT is mainly attributed to the additional formation of silver nanoparticles and to the possible formation and conversion of intermediates that are not formed and or converted at RT (thermodynamic limitation). Basing on this study, a possible mechanism of the photo-assisted SCR reaction over Ag@ZX-V catalyst is proposed.

Selective catalytic reduction of NOx over Cu- and Fe-exchanged zeolites and their mechanical mixture

SCR-NH3 activities of Cu-SAPO-34 (Cu-CZC) and Fe-Mordenite (Fe-MOR) and their mechanical mixture (50:50) were investigated in the temperature range 150–450 °C using operando FTIR spectroscopy. Structural and textural studies assessed the quality of the material synthesis, while in situ IR characterisation allowed the quantification of the acidic sites at the surface of the zeolites, as well as the cationic distribution inside the pores. As expected, Cu-CZC showed high NOx activity at lower temperatures (75% of NOx conversion at T < 300 °C), while Fe-MOR was more active (>85%) at higher temperatures (300–450 °C). The co-presence of Cu and Fe in the mechanical mixture catalyzes the undesirable oxidation of ammonia and leads to the formation of NO, especially at high temperatures. However, the mechanical mixture of Cu-CZC and Fe-MOR has been found to efficiently operate in the presence of excess ammonia (NH3/NOx = 1.3) in a much broader temperature range comparing to the catalysts modified with only one transition metal (Fe or Cu) and also respect to a sample containing both cations in a single zeolitic framework, thus opening new opportunities in the catalytic reduction of NOx.