Catalyst characterization temperature-programmed reduction

Dicko, A., Song, X.M, Adnot, A., Sayari, A. (1994). Characterization of Platinum on Sulfated Zirconia Catalysts by Temperature Programmed Reduction. Journal of Catalysis, Vol.150, No.2, (December 1994), pp. 254-261, ISSN 0021-9517... 

Catalysts were characterized using SEM (Hitachi S-4800, operated at 15 keV for secondary electron imaging and energy dispersive spectroscopy (EDS)), XRD (Bruker D4 Endeavor with Cu K radiation operated at 40 kV and 40 mA), TEM (Tecnai S-20, operated at 200 keV) and temperature-programmed reduction (TPR). Table 1 lists BET surface area for the selected catalysts. 

In this work, the catalytic reforming of CH4 by CO2 over Ni based catalysts was investigated to develop a high performance anode catalyst for application in an internal reforming SOFC system. The prepared catalysts were characterized by N2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). 

T. H. Tsai, J. W. Lane, and C. S. Lin Temperature-Programmed Reduction for Solid Materials Characterization, Alan Jones and Brian McNichol Catalytic Cracking Catalysts, Chemistry, and Kinetics,... 

In this study butyl acetate (AcOBu) was hydrogenolysed to butanol over alumina supported Pt, Re, RePt and Re modified SnPt naphtha reforming catalysts both in a conventional autoclave and a high throughput (HT) slurry phase reactor system (AMTEC SPR 16). The oxide precursors of catalysts were characterized by Temperature-Programmed Reduction (TPR). The aim of this work was to study the role and efficiency of Sn and Re in the activation of the carbonyl group of esters. 

The catalysts were characterized by inductively coupled plasma emission spectroscopy (ICP-ES Perkin Elmer Optima 3300RL) to determine cobalt content, x-ray diffraction (XRD Bruker A-500) with crystallite size determination using the Rietveld method, and temperature-programmed reduction (Zeton Altamira AMI-200) using 30 ml/min 10% H2/Ar and a ramp rate of 10°C/min. Surface area... 

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization rate. 

Structural characterization of the prepared Co/alumina catalysts was studied by using the following techniques Brunauer-Emmett-Teller (BET), temperature-programmed reduction (TPR), H2 chemisorption by temperature-programmed desorption (TPD) with 02 pulse reoxidation, and powder x-ray diffraction (XRD). 

Mg pyrovanadate (Mg2V207) was also found to be a selective catalyst for this reaction (30). A later study further showed that the catalytic performance of Mg2V207 was insensitive to the method of preparation, such that there were only minor differences whether or not the oxide contained small amounts of potassium (25). In contrast, the presence of K in Mg orthovanadate degraded its selectivity noticeably. Temperature-programmed reduction with H2 and electrical conductivity characterization in the presence of propane showed that Mg pyrovanadate could be reduced by both H2 and propane faster than Mg orthovanadate containing K (31). 

Temperature Programmed Reduction. Temperature-programmed reduction (TPR), one of the indirect analysis methods, yielded data that suggested that Sn was not reduced to zero-valent state (10,16). Burch (15) has reviewed early work on the characterization of this type of catalyst. Lieske and Volter (21) reported, based on the results obtained from TPR studies, that a minor part of the tin is reduced to the metal, and this Sn(O) combined with Pt to form "alloy clusters" but the major portion of the tin is reduced to only the... 

Temperature-programmed reduction (TPR) is normally used in the characterization of catalysts [18,91-93], In general, to carry out a TPR experiment, a reducing gas mixture, typically 5% hydrogen in nitrogen, flows continuously over the sample [92], The gas flow rate can be varied precisely using either built-in controls or an optional mass flow controller accessory. 

Kinetic studies focus on the selection of an adequate rate expression and determination of the unknown rate parameters it contains (eq 1). Generally, the rate is not measured directly but is derived from a measured quantity, conversion or concentration, at given operating conditions such as catalyst amount and feed rate. Apart from kinetic studies to determine the rate equation, other purposes of measuring rates are comparison of various catalyst formulations in screening of new catalysts, the time-dependent behavior of the catalyst actvity to predict its long term performance and to characterize catalysts such as in temperature programmed reduction (TPR) or sulphidation (TPS) studies. 

It was appreciated at the outset that the characterization of these materials would be an altogether more difficult problem than that of EUROPT-1, by reason of the lower metal content, and the bimetallic nature of EUROPT-4. It was hoped that study of the latter would help resolve some of the questions concerning the intimacy of mixing of the two metals in the functioning catalyst, but these queries have been only partially answered. Temperature programmed reduction (TPR) studies have confirmed the sensitivity of the reduction profile to experimental conditions and sample pretreatment but, notwithstanding reports in the liter-... 

Details of characterization by x-ray and electron diffraction, transmission electron microscopy and XPS are given elsewhere ( ). Temperature programmed reduction (TPR) studies using a 3%H2/N2 gas mixture, were performed on 40 mg catalyst samples in a tubular furnace (heating rate 10 C/min), using TCD and FID detection. Prior to TPR, the sample was heated in air at a specified temperature for 3h. 

In addition to the structure in the dehydrated state, the structure of supported vanadia catalysts under redox reaction conditions is directly related to the catalytic performance. Vanadia catalysts are usually reduced to some extent during a redox reaction, and the reduced vanadia species have been proposed as the active sites [4, 19-24]. Therefore, information on the valence state and molecular structure of the reduced vanadia catalysts is of great interest. A number of techniques have been applied to investigate the reduction of supported vanadia catalysts, such as temperature programmed reduction (TPR) [25-27], X-ray photoelectron spectroscopy (XPS) [21], electron spin resonance (ESR) [22], UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) [18, 28-32], X-ray absorption fine structure spectroscopy (XAFS) [11] and Raman spectroscopy [5, 26, 33-41]. Most of these techniques give information only on the oxidation state of vanadium species. Although Raman spectroscopy is a powerful tool for characterization of the molecular structure of supported vanadia [4, 29, 42], it has been very difficult to detect reduced supported... 

A wide range of techniques has been used on both fresh and used catalysts to characterize the nature of the oxide surface, for example X-ray powder diffraction (XRD) [10-12], UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS) [11, 12], Raman spectroscopy [10, 11, 14—17], X-ray photoelectron spectroscopy (XPS) [11, 12, 18], electron paramagnetic resonance (EPR) [12, 19], infrared spectroscopy [10, 20] and temperature programmed reduction (TPR) [16, 21]. Given the number of... 

The precursor and the calcined catalyst were characterized by various techniques such as nitrogen adsorption, mercury porosimetry, X-ray diffraction (XRD), atomic emission spectrometry by inductively coupled plasma (ICP), thermogravimetric analysis, and temperature-programmed reduction (TPR). More details about the catalyst preparation and characterization can be found in a previous work (22). 

The prepared catalysts and the chemical compositions measured by atomic absorption, are listed in Table 1. Complementary characterization experiments such as hydrogen chemisorption in a pulse apparatus and temperature-programmed reduction (TPR) were performed using experimental systems and methods described in detail elsewhere [10]. 

The catalysts were characterized by BET surface area measurement, XRD, in-situ CO2 H2 chemisorption measurements, and Temperature Programmed Reduction (TPR). CO2 hydrogenation was carried out in a fixed bed flow reactor made of stainless steel. Prior to the activity studies, the catalysts were reduced in 99.99 % H2 flow at 723K for 12hrs. After this, the reaction gas (H2/CO2 = 3) was introduced into the reactor at 573K at 10 atm. The gas phase effluents were analyzed by on-line GC. 

---