On-line Product Analysis Research Articles

Electrocatalytic nitrogen reduction in continuous-flow cell via water oxidation at ambient conditions: Promising for ammonia or diazene?

Electrochemical nitrogen reduction reaction (eNRR) is recognized as an alternative green approach to the traditional energy-demanding and fossil-based catalytic processes (e.g. Haber Bosch). In this study, we implement eNRR in a proton exchange membrane (PEM) water electrolyzer in which nitrogen (N2) is fed in the cathode. This operation mode has been suggested as a way to overcome mass transfer limitations, however, there is a lack of developed evaluation protocols for appropriate product identification. Herein, we exemplify the spirit of the evaluation protocols for gas phase operation at the device level with a combination of online product analysis and isotopic labeling. Our protocol involves control experiments by replacing the cathodic N2 feed with (i) inert gas (i.e. Ar) and (ii) isotopic labeled 15N2 and by replacing the anodic water feed with isotopic labeled D2O. Taking advantage of the gas phase operation in the cathode product analysis is realized with online techniques i.e. quadrupole mass-spectrometer (QMS) and Fourier transform infrared (FTIR) spectrometer. This allows us to verify the production of diazene (N2H2) resulted from genuine N2 reduction, rather than from nitrogen-containing contaminants. Our methodology provides a pathway for how the false positive results can be eliminated in the gas phase study and a platform for follow-up studies using promising or exotic catalysts in the cathode, especially to validate the eNRR products or discover more products.

Spectro-kinetics of the methanol to hydrocarbons reaction combining online product analysis with UV–vis and FTIR spectroscopies throughout the space time evolution

The well-studied methanol to hydrocarbons reaction over a ZSM-5 zeolite catalyst has been used to develop a spectro-kinetic approach to obtain an overall reaction mechanism involving both retained species and gas-phase products. We combined two in situ spectroscopic techniques (ultraviolet–visible and Fourier-transform infrared spectroscopies) with online product analysis to obtain the time- and space time-resolved evolution of the entire reaction media. A ZSM-5 zeolite catalyst was tested in two commercial spectroscopic cells at 400 °C using different space times (different inlet flow rates). Specifically, our work focusses on the effect of the space time (key parameter in any kinetic study) and how to tune other parameters such as partial pressure of methanol to resolve, from the spectroscopic and gas-phase points of view, the mechanisms of reaction and deactivation. Our approach reinforces the previous interpretation of these two combined networks in the selected reaction, thus, proving that the spectro-kinetic approach is a robust methodology to simultaneously build overall reaction and deactivation mechanisms.

A Versatile Ambient‐to‐High‐Pressure Reaction Transmission Cell for in situ/operando Infrared Spectroscopic Investigations

AbstractInvited for this month's cover is the group of Angelika Brücker at the Leibniz Institute for Catalysis in Rostock (Germany). The cover picture shows a self‐developed stainless‐steel reaction cell for operando transmission FTIR studies of heterogeneous catalytic gas‐phase reactions at pressures up to 30 bar and temperatures up to 300°C, which is connected to a mass spectrometer for online product analysis. The performance of the cell has been tested in three types of CO2 hydrogenation reactions (CO2 Fischer‐Tropsch synthesis, CO2 methanation, CO2 conversion to dimethyl ether) on various solid catalysts implemented as self‐supporting wafers. Catalytic data obtained with this cell showed the same trends as those measured in a fixed‐bed plug‐flow reactor, thus confirming their reliability. Read the full text of their Full Paper at 10.1002/cmtd.202100024.

Cover Picture: A Versatile Ambient‐to‐High‐Pressure Reaction Transmission Cell for in situ/operando Infrared Spectroscopic Investigations (Chemistry ‐ Methods 7/2021)

The Front Cover shows a self-developed stainless-steel reaction cell for operando transmission FTIR studies of heterogeneous catalytic gas-phase reactions at pressures up to 30 bar and temperatures up to 300°C, which is connected to a mass spectrometer for online product analysis. The performance of the cell has been tested in three types of CO2 hydrogenation reactions (CO2 Fischer-Tropsch synthesis, CO2 methanation, CO2 conversion to dimethyl ether) on various solid catalysts implemented as self-supporting wafers. Catalytic data obtained with this cell showed the same trends as those measured in a fixed-bed plug-flow reactor, thus confirming their reliability. More information can be found in the Full Paper by Jane Weiß et al.

Implications of Co‐Feeding Water on the Growth Mechanisms of Retained Species on a SAPO‐18 Catalyst during the Methanol‐to‐Olefins Reaction

AbstractThe dynamics of retained and deactivating species in a SAPO‐18 catalyst during the methanol‐to‐olefins reaction have been followed using a combination of ex‐situ and in‐situ techniques in differential and integral reactors.The retained species were analyzed using extraction, in‐situ FTIR and in‐situ UV‐vis spectroscopies combined with online product analysis (gas chromatography and mass spectrometry). The composition of the extracted soluble species was determined using gas chromatography‐mass spectrometry and that of the insoluble species using high‐resolution mass spectrometry. We observe a decrease in the formation and degradation rates of retained species when co‐feeding water, whereas the extent of the decreases is the same across the entire spectrum of retained molecules. This indicates that co‐feeding water unselectively quenches the formation of active and deactivating species. At the same time, the catalyst has an extended lifetime when co‐feeding water due to the diffusion of species (particularly olefins) out of the SAPO‐18 crystals, and subsequent growth of heavy polycyclic aromatic structures that imply less deactivation. These conclusions can be extrapolated to other MTO catalysts with relatively similar pore topology such as SAPO‐34 or SSZ‐13 structures.

Silicon redistribution, acid site loss and the formation of a core–shell texture upon steaming SAPO-34 and their impact on catalytic performance in the Methanol-to-Olefins (MTO) reaction

SAPO-34 is a commercially-implemented silicoaluminophosphate catalyst for selective high yield production of ethene and propene from methanol, but high temperature regeneration in the presence of steam leads to its deactivation. A comprehensive investigation of the effect of prolonged hydrothermal treatment on the structure and properties of SAPO-34 explains the changes in its catalytic methanol-to-olefins (MTO) performance. Microcrystalline powdered SAPO-34 (ca. 3 µm crystals, Al17.1P15.6Si3.3O72) and two batches of larger single crystals of SAPO-34 of different Si concentration (20–100 µm; Al17.3P14.7Si4.0O72 and Al17.7P12.3Si5.9O72) were steamed (pH2O = 0.95 atm) at 873–1023 K for up to 240 h. The acidity (NH3-TPD), crystallinity (PXRD), framework cation environment (solid-state 27Al, 29Si and 31P MAS NMR) and porosity were followed for all materials; larger crystals were amenable to single crystal X-ray diffraction, FIB-SEM and synchrotron IR microspectroscopy, including operando study during methanol and dimethyl ether conversions. Some level of steaming improved the lifetime of all SAPO-34 materials in MTO catalysis without affecting their olefin selectivity, although more severe conditions led to the formation of core–shell structures, microporosity loss and eventually at 1023 K, recrystallization to a dense phase. All these irreversible changes occurred faster in crystals with higher Si contents. The initial increase in catalytic lifetime results from an activated reduction in acid site density (Eact = 146(18) kJ mol−1), a result of redistribution of Si within the SAPO framework without porosity loss. Operando IR with online product analysis during methanol conversion suggests similar reaction pathways in calcined and steamed crystals, but with greatly reduced methoxy group densities in the latter. The gradual development of optically dark crystal cores upon progressive steaming was shown by FIB-SEM to be due to the formation of regions with meso- and macropores, and these were shown by IR mapping to possess low hydroxyl densities.

Suppressing H2 Evolution and Promoting Selective CO2 Electroreduction to CO at Low Overpotentials by Alloying Au with Pd

CO 2 electroreduction is a promising technology to produce chemicals and fuels from renewable resources. Polycrystalline and nanostructured metals have been tested extensively while less effort has been spent on understanding the performance of bimetallic alloys. In this work, we study compositionally variant, smooth Au-Pd thin film alloys to discard any morphological or mesoscopic effect on the electrocatalytic performance. We find that the onset potential of CO formation exhibits a strong dependence on the Pd content of the alloys. Strikingly, palladium, a hydrogen evolution catalyst with reasonable exchange current density, suppresses hydrogen evolution when alloyed with gold in the presence of CO 2 . Cyclic voltammetry, in situ surface enhanced infrared absorption spectroscopy, and potential-dependent online product analysis strongly suggest that by alloying Au with Pd a significant increase in the surface coverage of adsorbed CO occurs with increasing Pd content at low overpotentials (e.g., approximately -0.35 V vs RHE). Such an increase in CO coverage suppresses H 2 evolution due to the lack of vacant active sites. Moreover, the overall increase in the binding energy with the CO 2 intermediates gained with the addition of Pd increases the CO production at low overpotentials, where polycrystalline Au suffers from poor CO 2 adsorption and poor selectivity for CO production. These results show that promising CO 2 reduction electrode materials (e.g., Au) can be alloyed not only to tune the catalyst's activity but also to deliberately decrease the availability of surface sites for competitive H 2 evolution.

Rational design of CrOx/LaSrMnCoO6 composite catalysts with superior chlorine tolerance and stability for 1,2-dichloroethane deep destruction

1,2-dichloroethane (1,2-DCE) is a representative industrial chlorinated volatile organic compound (CVOC) making great hazardous to the environment and human health. In this work, LaSrMnCoO6 (LSMC) double perovskite-type materials with high thermal stability and coke resistance in 1,2-DCE oxidation were prepared by a facile sol-gel method. Based on this, a series of CrOx/LaSrMnCoO6 catalysts (Cr/LSMC, CrOx loading = 5 to 20 wt.%) which combine the merits of CrOx (high activity and chlorine tolerance) and LaSrMnCoO6 were synthesized and adopted in deep oxidation of 1,2-DCE for the first time. As expected, obvious synergistic effects between CrOx and LSMC on 1,2-DCE destruction were observed. Amongst, 10 wt.% CrOx/LaSrMnCoO6 (10Cr/LSMC) shows the best catalytic activity with 90% of 1,2-DCE destructed at 400 °C. Furthermore, the outstanding catalytic durability and water resistance of 10Cr/LSMC in 1,2-DCE oxidation were also demonstrated. In addition to this, the reaction pathway of 1,2-DCE decomposition over Cr/LSMC materials was discussed based on the results of online product analysis. We found that the enhanced catalytic performance of Cr/LSMC materials can be reasonably attributed to their high reducibility, excellent 1,2-DCE adsorption capability, and large amounts of surface active lattice oxygen species. It can be anticipated that the Cr/LSMC catalysts are promising materials for CVOC elimination and the results from this work could also provide some new insights into the design of catalysts for CVOC efficient destruction.

Phase Coexistence of Multiple Copper Oxides on AgCu Catalysts during Ethylene Epoxidation

Alloy catalysts under reaction conditions are complex entities. In oxidizing atmospheres, multiple phases can coexist on a catalyst’s surface as a result of phase segregation and preferential oxidation. Such a scenario can result in unusual substoichiometric and metastable phases that could play important roles in catalytic processes. For instance, AgCu alloys—known to exhibit enhanced epoxide selectivity in partial oxidation of ethylene—form an oxide-like surface structure under reaction conditions. Under these conditions, copper oxides are stable, while silver oxides are not. Consequently, copper segregates to the alloy’s surface and forms an oxide overlayer. Little is known about the structure or function of such overlayers, and it is unknown whether they play an active role in the catalyst’s enhanced selectivity. In order to develop a clearer picture of such catalysts, the current work utilizes several in situ spectroscopic and microscopic techniques to examine the copper oxide phases that form when AgCu is exposed to epoxidation conditions. It is found that several forms of oxidic Cu coexist simultaneously on the active catalyst’s surface, namely, CuO, Cu2O, and some previously unreported form of oxidized Cu, referred to here as CuxOy. Online product analysis, performed during the in situ spectroscopic measurements, shows that increased epoxide selectivity is correlated with the presence of mixed copper oxidation states and the presence of the CuxOy species. These results support previous theoretical predictions that oxidic copper overlayers on silver play an active role in epoxidation. These results furthermore emphasize the need for in situ spectromicroscopic methods to understand the complexity of alloy catalysts.

Ethylene Epoxidation at the Phase Transition of Copper Oxides.

Catalytic materials tend to be metastable. When a material becomes metastable close to a thermodynamic phase transition it can exhibit unique catalytic behavior. Using in situ photoemission spectroscopy and online product analysis, we have found that close to the Cu2O-CuO phase transition there is a boost in activity for a kinetically driven reaction, ethylene epoxidation, giving rise to a 20-fold selectivity enhancement relative to the selectivity observed far from the phase transition. By tuning conditions toward low oxygen chemical potential, this metastable state and the resulting enhanced selectivity can be sustained. Using density functional theory, we find that metastable O precursors to the CuO phase can account for the selectivity enhancements near the phase transition.

Comparison of Fast Pyrolysis Behavior of Cornstover Lignins Isolated by Different Methods

The effect of lignin isolation methods on lignin fast pyrolysis was investigated utilizing an online product analysis methodology to give high mass balance closure for the products. Lignin samples with high purity were isolated from cornstover using three methods: Bjorkman milling, organosolv extraction, and gamma-valerolactone (GVL) extraction. Although milled wood lignin has been extensively studied, characterization and the fast pyrolysis of milled cornstover lignin has not been previously reported. The current study shows that the milled cornstover lignin contains a higher molecular weight and more aryl ether linkages relative to organosolv and GVL extracted cornstover lignin. During fast pyrolysis, considerably more phenolics, especially those with side chain double bonds derived from aryl ether cleavage, were formed from the milled cornstover lignin concomitant with less char formation.

Co-Electrolysis, Quo Vadis?

This work focuses on the impact of reaction parameters of high-temperature co-electrolysis of carbon dioxide and water on the electrochemical performance and product gas distribution. Experiments have been performed with a conventional electrode (cathode) supported solid oxide cell. The electrochemical performance was investigated by I/V-curve measurements and impedance spectroscopy. The temperature was varied in the range of 750 to 900 °C. At 900 °C the impact of different feed gas compositions was investigated. The provided volumetric water vapor content was changed from 40 % with 20 % H2 up to 47.5 % with 5 % H2 in addition to the varied CO2 to H2O ratios 0, 1:1, 1:2 and 1:3. Parameter controlled syngas tailoring was shown by ramps of increasing current densities (at 0.001 mA·s-1) and coupled online product analysis at feed flow rates of 2, 3 and 6 nl·h-1, confirming its principle.

Combined Operando X-ray Diffraction/Raman Spectroscopy of Catalytic Solids in the Laboratory: The Co/TiO2 Fischer-Tropsch Synthesis Catalyst Showcase.

A novel laboratory setup for combined operando X‐ray diffraction and Raman spectroscopy of catalytic solids with online product analysis by gas chromatography is presented. The setup can be used with a laboratory‐based X‐ray source, which results in important advantages in terms of time‐on‐stream that can be measured, compared to synchrotron‐based experiments. The data quality was much improved by the use of a relatively high‐energy MoKα radiation instead of the more conventional CuKα radiation. We have applied the instrument to study the long‐term deactivation of Co/TiO2 Fischer–Tropsch synthesis (FTS) catalysts. No sign of Co sintering or bulk oxidation was found during the experiments. However, part of the metallic Co was converted into cobalt carbide (Co2C), at elevated pressure (10 bar). Furthermore, graphitic‐like coke species are clearly formed during FTS at atmospheric pressure, whereas at elevated pressure fluorescence hampered the interpretation of the measured Raman spectra.

Application of infrared reflection and Raman spectroscopy for quantitative determination of fat in potato chips

Potato chips are important products in the snack industry. The most significant parameter monitored during their quality control process is fat content. The Soxhlet method, which is applied for this purpose, is time consuming and expensive. We demonstrate that both infrared and Raman spectroscopy can effectively replace the extraction method.Raman, mid-infrared (MIR) and near-infrared (NIR) spectra of the homogenised laboratory-prepared chips were recorded. On the basis of obtained spectra, partial least squares (PLS) calibration models were constructed. They were characterised by the values of relative standard errors of prediction (RSEP) in the 1.0–1.9% range for both calibration and validation data sets. Using the developed models, six commercial products were successfully quantified with recovery in the 98.5–102.3% range against the AOAC extraction method. The proposed method for fat quantification in potato chips based on Raman spectroscopy can be easily adopted for on-line product analysis.

Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques.

We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

Electrocatalytic Hydrogenation of 5‐Hydroxymethylfurfural in the Absence and Presence of Glucose

Electrocatalytic hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-dihydroxymethylfuran (DHMF) or other species, such as 2,5-dimethylfuran, on solid metal electrodes in neutral media is addressed, both in the absence and in the presence of glucose. The reaction is studied by combining voltammetry with on-line product analysis by using HPLC, which provides both qualitative and quantitative information about the reaction products as a function of electrode potential. Three groups of catalysts show different selectivity towards: (1) DHMF (Fe, Ni, Ag, Zn, Cd, and In), (2) DHMF and other products (Pd, Al, Bi, and Pb), depending on the applied potential, and (3) other products (Co, Au, Cu, Sn, and Sb) through HMF hydrogenolysis. The rate of electrocatalytic HMF hydrogenation is not strongly catalyst-dependent because all catalysts show similar onset potentials (-0.5 ± 0.2 V) in the presence of HMF. However, the intrinsic properties of the catalysts determine the reaction pathway towards DHMF or other products. Ag showed the highest activity towards DHMF formation (up to 13.1 mM cm(-2) with high selectivity> 85%). HMF hydrogenation is faster than glucose hydrogenation on all metals. For transition metals, the presence of glucose enhances the formation of DHMF and suppresses the hydrogenolysis of HMF. On poor metals such as Zn, Cd, and In, glucose enhances DHMF formation; however, its contribution in the presence of Bi, Pb, Sn, and Sb is limited. Remarkably, in the presence of HMF, glucose hydrogenation itself is largely suppressed or even absent. The first electron-transfer step during HMF reduction is not metal-dependent, suggesting a non-catalytic reaction with proton transfer directly from water in the electrolyte.

X-ray absorption spectroscopy and heterogeneous catalysis: Performances at the SOLEIL's SAMBA beamline

New plug-flow cells suitable for the X-ray absorption spectroscopy (XAS) study of heterogeneous catalysts by transmission and fluorescence detection modes are described. These cells are also suitable for combination with Raman spectroscopy providing valuable complementary information on the state of the catalyst in working conditions. On-line product analysis is obtained either by mass spectrometry or Raman spectroscopy providing a full description of the activity of the catalyst. These tools are successfully used for time-resolved investigations of heterogeneous catalysts in working conditions using the capability of the Quick-XAS monochromators installed at the SAMBA-SOLEIL beamline. The performances of the full set-up including spectrometers and reaction cells are illustrated by a study of the calcination step of a bimetallic hydrodesulphurisation catalyst and of the activation/reaction processes of a Fischer–Tropsch catalyst.

Complete Quantitative Online Analysis of Methanol Electrooxidation Products via Electron Impact and Electrospray Ionization Mass Spectrometry

We report on a novel approach for complete quantitative online product analysis in electrocatalytic reactions, combining electron impact ionization mass spectrometry (EI-MS) and electrospray ionization mass spectrometry (ESI-MS) for simultaneous detection of both volatile and nonvolatile reaction products. The potential of this method is demonstrated using continuous methanol oxidation in a flow cell. The overall reaction rate was followed via the Faradaic current; CO(2) formation was monitored mass spectrometrically via a membrane inlet system, and formaldehyde and formic acid were detected by ESI-MS after a derivatization-extraction-separation procedure introduced recently (Zhao, W.; Jusys, Z.; Behm, R. J. Anal. Chem.2010, 82, 2472-2479) providing quantitative data on the product distribution. In a more general sense, this approach is applicable for a wide range of reactions at the solid-liquid interface or in liquid phase.

Rapeseed oil methyl ester pyrolysis: On-line product analysis using comprehensive two-dimensional gas chromatography

Thermochemical conversion processes play a crucial role in all routes from fossil and renewable resources to base chemicals, fuels and energy. Hence, a fundamental understanding of these chemical processes can help to resolve the upcoming challenges of our society. A bench scale pyrolysis set-up has been used to study the thermochemical conversion of rapeseed oil methyl ester (RME), i.e. a mixture of fatty acid methyl esters. A GC × GC, equipped with both a flame ionization detector (FID) and a time-of-flight mass spectrometer (TOF-MS), allows quantitative and qualitative characterization of the reactor feed and product. Analysis of the latter is accomplished using a dedicated high temperature on-line sampling system. Temperature programmed analysis, starting at −40 °C, permits effluent characterization from methane up to lignoceric acid methyl ester (C 25H 50O 2), in a single run of the GC × GC. The latter combines a 100% dimethylpolysiloxane primary column with a 50% phenyl polysilphenylene-siloxane secondary column. Modulation is started when the oven temperature reaches 40 °C, thus dividing the chromatogram in a conventional 1D and a comprehensive 2D part. The proposed quantification approach allows to combine the quantitative GC × GC analysis with 2 other on-line 1D GC analyses, resulting in a complete and detailed product composition including the measurement of CO, CO 2, formaldehyde and water. The GC × GC reveals that the product stream contains a huge variety of valuable products, such as linear alpha olefins, unsaturated esters and aromatics, that could not have been identified and quantified accurately with conventional 1D GC because of peak overlap.

Direct ethanol fuel cells: The effect of the cell discharge current on the products distribution

In the present work the results of the continuous and on-line product analysis during a Direct Ethanol Polymer Electrolyte Membrane Fuel Cell operation (DE-PEMFC) are presented. The effect of both cell discharge current and operating temperature on (a) the ethanol's conversion, (b) the reaction products distribution and (c) the reaction yield towards each released product, is examined. The MEA used during the experiments is comprised of a PtRu/C anode, a Nafion®-115 membrane and a Pt/C cathode. It is found that the increase of the cell current and the operating temperature lead to an increase of the ethanol conversion. The maximum ethanol conversion is found to be 4.6% and it is recorded when the cell current is 120mA and the cell temperature is 90°C. The main products detected during the fuel cell operation are acetaldehyde (CH3CHO), acetic acid (CH3COOH) and small amounts of carbon dioxide (CO2). The selectivity of acetaldehyde ranges from 45% to 70%, the selectivity of acetic acid ranges from 25% to 45% and the selectivity of CO2 ranges from 5% to 15%. As it concerns the reaction yield towards each product, it is found that the increase of the temperature results in an increase of the yield. Furthermore, from the Arrhenius plots based on the products formation rate, it is found that the acetaldehyde is favored over PtRu/C compared to the other products. Finally, based on the apparent activation energy of the CO2 formation rate (50kJmol−1), it is concluded, that the C–C bond breakage of the ethanol molecule is difficult to occur over the anode catalyst.