Effective bulk and surface temperatures of the catalyst bed of FT-IR cells used for in situ and operando studies.

The temperature prevailing in the catalyst bed of three different IR spectroscopic reaction cells was assessed by means of thermocouples, an optical pyrometer and reaction rate measurements. One of the cells was a custom-made transmission FT-IR cell for use with thin wafers and the two others were commercial Harrick and Spectra-Tech diffuse reflectance FT-IR (DRIFTS) cells used for the analysis of powdered samples. The rate of CO methanation measured over a 16 wt% Ni/alumina catalyst was used as a means to derive the effective temperature prevailing in the IR cells from that existing in a traditional (non-spectroscopic) reactor having a well-controlled temperature. The sample bed of these three IR cells exhibited a significantly lower temperature than that of the corresponding measure thermocouple, which was yet located in or close to the sample bed. The comparison of Arrhenius plots enabled us to determine a temperature correction valid over a large temperature range. The use of an optical pyrometer was assessed with a view to determining the temperature of the surface of the powdered beds and that at the centre of the wafer. The optical pyrometer proved useful in the case of the catalyst powder, which behaved as a black non-reflecting body. In contrast, the temperature reading was inaccurate in the case of the pressed wafer, probably due to the shiny surface and minute thickness of the wafer, which led to a significant portion of the IR radiation of the surroundings being reflected by and transmitted through the wafer. The optical pyrometer data showed that the temperature of the surface of the powdered beds was significantly lower than that of the bulk of the bed, and that the total flow rate and composition did not affect this value. This work emphasises that the effective bed temperature in spectroscopic cells can be significantly different from that given by measure thermocouples, even when located in the vicinity of the sample, but that the calibration curves derived from rate measurements can be used to overcome this problem.

[1]  D. Rooney,et al.  A modified commercial DRIFTS cell for kinetically relevant operando studies of heterogeneous catalytic reactions , 2008 .

[2]  B. Weckhuysen,et al.  In situ UV–VIS diffuse reflectance spectroscopy–on-line activity measurements , 1998 .

[3]  A. Dent,et al.  Tracing the conversion of aurichalcite to a copper catalyst by combined X-ray absorption and diffraction , 1991, Nature.

[4]  Christophe Dujardin,et al.  Modelling and optimization of IR cell devoted to in situ and operando characterization of catalysts , 2013 .

[5]  B. Weckhuysen,et al.  Dealing with a local heating effect when measuring catalytic solids in a reactor with Raman spectroscopy. , 2006, Physical chemistry chemical physics : PCCP.

[6]  Jens R. Rostrup-Nielsen,et al.  Atom-Resolved Imaging of Dynamic Shape Changes in Supported Copper Nanocrystals , 2002, Science.

[7]  F. Ribeiro,et al.  Determination of the Au active site and surface active species via operando transmission FTIR and isotopic transient experiments on 2.3 wt.% Au/TiO2 for the WGS reaction , 2012 .

[8]  C. D. Baertsch,et al.  Spatially resolved in situ FTIR analysis of CO adsorption and reaction on Pt/SiO2 in a silicon microreactor , 2009 .

[9]  Søren Dahl,et al.  Methanation of CO over nickel: Mechanism and kinetics at high H2/CO ratios. , 2005, The journal of physical chemistry. B.

[10]  C. Hardacre,et al.  Investigating the mechanism of the H2-assisted selective catalytic reduction (SCR) of NOx with octane using fast cycling transient in situ DRIFTS-MS analysis , 2010 .

[11]  J. Lercher,et al.  In situ IR study of the nature and mobility of sorbed species on H-FER during but-1-ene isomerization , 2002 .

[12]  C. Hardacre,et al.  Guest sorption and desorption in the metal-organic framework [Co(INA)(2)] (INA=isonicotinate)--evidence of intermediate phases during desorption. , 2004, Dalton transactions.

[13]  Bert M. Weckhuysen,et al.  Determining the active site in a catalytic process: Operando spectroscopy is more than a buzzword , 2003 .

[14]  F. Meunier.  The design and testing of kinetically-appropriate operando spectroscopic cells for investigating heterogeneous catalytic reactions. , 2010, Chemical Society reviews.

[15]  M. Daturi,et al.  CO and NO adsorption for the IR characterization of Fe2+ cations in ferrierite: An efficient catalyst for NOx SCR with NH3 as studied by operando IR spectroscopy , 2010 .

[16]  G. Mickelson,et al.  Design and operation of a high pressure reaction cell for in situ X-ray absorption spectroscopy , 2007 .

[17]  Y. Schuurman,et al.  An operando DRIFTS investigation into the resistance against CO2 poisoning of a Rh/alumina catalyst during toluene hydrogenation. , 2012, Physical chemistry chemical physics : PCCP.

[18]  Charles T. Campbell,et al.  Design and operating characteristics of a transient kinetic analysis catalysis reactor system employing in situ transmission Fourier transform infrared , 2006 .

[19]  R. Feidenhans'l,et al.  In situ cell for combined XRD and on-line catalysis tests : studies of Cu-based water gas shift and methanol catalysts , 1991 .

[20]  M. Bañares,et al.  Structure–activity relationships in alumina-supported molybdena–vanadia catalysts for propane oxidative dehydrogenation , 2004 .

[21]  M. Flytzani-Stephanopoulos,et al.  Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O2 water–gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates , 2007 .

[22]  S. Phanichphant,et al.  Quantitative analysis of adsorbate concentrations by diffuse reflectance FT-IR. , 2007, Analytical chemistry.

[23]  M. Boudart,et al.  Experimental criterion for the absence of artifacts in the measurement of rates of heterogeneous catalytic reactions , 1982 .

[24]  Philippe Bazin,et al.  Studying the NOx-trap mechanism over a Pt-Rh/Ba/Al2O3 catalyst by operando FT-IR spectroscopy , 2003 .