Reduction temperature-programmed

Reduction is an unavoidable step in the preparation of metallic catalysts. It is often also a critical step, because if it is not done correctly the catalyst may sinter or may not reach its optimum state of reduction. The reduction of a metal oxide MO by H2 is described by the equation 

Thermodynamics predicts under which conditions a catalyst can be reduced. As with every reaction, the reduction will proceed when the change in Gibbs free energy, AG, has a negative value. Equation (2-2) shows how AG depends on pressures and temperature  

If the reaction in which the metallic fraction serves as a catalyst produces water as a by-product, it may well be that the catalyst converts back to an oxide. One should always be aware that in fundamental catalytic studies, where reactions are usually carried out under differential conditions (i.e. low conversions) the catalyst may be more reduced than is the case under industrial conditions. An example is the behavior of iron in the Fischer-Tropsch reaction, where the industrial iron catalyst at work contains substantial fractions of Fe304, while fundamental studies report that iron is entirely carbidic and in the zero-valent state when the reaction is run at low conversions [6], 

Reduction reactions of metal oxides by hydrogen start with the dissociative adsorption of H2, which is a much more difficult process on oxides than on metals. Atomic hydrogen takes care of the actual reduction. Depending on how fast or how slow the dissociative adsorption is in comparison to the subsequent reduction reactions which comprise diffusion of atomic hydrogen into the lattice, reaction with oxygen and removal of the hydroxyl species formed, two limiting cases are distinguished [1,7]. 

In temperature programmed reduction one follows the degree of reduction of the catalyst as a function of time, while the temperature increases at a linear rate. We follow the theoretical treatment of the TPR process as given by Hurst et al. [1] and by Wimmers et al. [8]. Formally, one can write the rate expression for the reduction reaction in (2-1), under conditions where the reverse reaction from metal to oxide can be ignored, as 

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. 

The consumption of hydrogen was monitored with a TCD held constantly at 100°C and recorded at a signal rate of 1 point/s. The hydrogen consumption was quantified by means of calibration with pure CuO (Merck 99.9%). The temperature of the sample bed was measured by means of a thermocouple inside the U-tube (with tip within the catalyst bed), and followed an exact linear ramp throughout the TPR run. A cold trap was used to prevent water passing through the TCD. The TPR experimental conditions were selected in agreement with criteria reported elsewhere [89], 

From calorimetric TPR-TPO experiments heats of reduction and reoxidation of eationic or metal species can be determined. Data obtained from these experiments may provide kinetie data of theoretical significance as well as an insight into the mechanism of the reduetion processes. 

TPR profiles of copper exchanged ETS-10, obtained by differential scanning calorimetry (DSC) and carried out with a hydrogen stream in heUum, are presented in Fig. 3.11 [26]. All the reduction profiles show complex structure, in which a stepwise reduction of CuO to Cu through CU2O intermediates occurred with overlapping of the two peaks. By analysis of this profiles authors gained useful information con- 

This coupling can be used for characterization of acidic or basic character of solid catalysts, and for study of solid-gas reactions. Systems used for these measurements are usually modified DSC instruments connected with GC/MS by a heated capillary tube [28-32]. In a typical experiment small pulses of probe gas are injected at regular intervals in to the carrier gas stream from a gas sampling valve. The gas flows are regulated by mass flow controllers. The concentration of ammonia down-stream of the sample is monitored with the GC/MS and heat evolution with the calorimeter. 

Isothermal titration calorimetry is a technique that can directly measure liquid-solid or liquid-liquid interactions. This method has been used for determination of acid-base properties of solid catalysts in an inert phase (n-decane), for determination of heats of reaction in liquid phase (alkylation, anisole+benzoic anhydride on H-Beta zeolite), and for determination of heats of adsorption of different pollutants on an adsorbent [33], It is also recognized as the only technique that can directly measure the binding energies of biological processes such as protein-ligand binding and protein-protein binding [34]. 

Instrument that is usually employed in this technique is differential heat flow calorimeter of Tian-Calvet type equipped by a stirring system. A programmable 

A common method used in the characterization of catalysts is the temperature programmed reduction. This method consists in passing a reducing gas (usually H2 diluted in an inert) with increasing programmed temperature. The reduction rate can be determined by the H2 consumption needed for the reduction of the oxide to a metal or to some intermediate phase, by measuring continuously the vmreacted H2 in the exit gas. The reduction depends on the composition and structure of the reducible oxide and can be identified by one or more peaks at different temperatures. The results provide also information about the reduction of bimetals, oxidation state, and the interaction between the metal oxide and the support, besides the 

The reduction is thermodynamically possible, since the free energy change, as given by Eq. (6.57), depends on the oxide and the reaction conditions, namely. 

Quantitative analysis allows calculating the degree of reduction. This calculation is shown in Appendix quantifying the H2 consumption during the reduction. 

The degree of reduction is the ratio of the number of moles of hydrogen consumed for the reduction of a metal oxide and the stoichiometric number of moles of hydrogen needed to reduce it to the metal, or  

The profiles have different maximum temperatures. For the bulk NiO, the maximum is about 750 K, which is in accordance with the literature [25, 34, 35]. For the bulk CuO, the maximum is about 708 K. 

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Temperature-Programmed Reduction for Solid Materials Characterization, Alan Jones and Brian McNichol... 

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. 

Temperature-programmed reduction TPR was used to determine the reduction behaviors of the catalyst samples. It was carried out using 50 mg of a sample and a temperature ramp from 35 to 800°C at 5°C/min. The carrier gas was 5% H2 in Ar. A cold trap was placed before the detector to remove water produced during the reaction. 

A. Jones and B.D. McNicol (eds.), Temperature Programmed Reduction for Solid Materials and Characterization, New York M. Dekker, 1986... 

Fig. 2. Temperature-programmed reduction profiles for Ni2P/Si02, Ni2P/Al20j, and Ni2P /C-AI2O3.

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). 

Physical properties of the prepared catalysts were measured by an adsorption analyzer [Quantachrome Co., Autosorb-lC]. The structure of prepared catalysts were investigated by XRD [Simmazdu Co., XRD-6000] with a Cu-Ka radiation source (X = 1.54056 A), voltage of 40.0 kV, ciurent of 30.0 mA and scan speed of 5.0 deg/min. Also, temperature-programmed reduction (TPR) profiles of the samples were investigated by a sorption analyzer [Micromeritics Co., Autochem II] and obtained by heating the samples from room temperature to 1100°C at a rate of lOTl/min in a 5 % H2/Ar gas flow (50 ml/min). 

Figure 4.20. Experimental set-ups for temperature programmed reduction, oxidation and desorption. Upper left The reactor is inside the oven, the temperature of which can be increased linearly with time. Gas consumption by the catalyst is monitored by the change in thermal conductivity of the gas mixture it is essential to remove traces of water, etc. because these would affect the thermal conductivity measurement. Lower-left ...

Temperature-programmed reaction methods form a class of techniques in which a chemical reaction is monitored while the temperature increases linearly in time. Several forms are in use temperature-programmed reduction, oxidation and sulfidation. 

Surface areas were determined from the adsorption isotherms of nitrogen at 77 K, using a Micromeritics ASAP 200 instrument. Powder X-ray diffraction patterns were obtained with a CGR theta 60 instrument using CuKa monochromated radiation. Reducibility and the amount of Cu species were determined by temperature programmed reduction (TPR) with H2 (H2/Ar 3/97, vol/vol). The experimental set up has been described previously [6]. 

Maximum temperatures and hydrogen consumption during the temperature programmed reduction of Cu/oxides by hydrogen, and NO taken up by Cu atom. 

Figure 2. Temperature programmed reduction profiles of Cu on zirconia and suifated zirconia with increasing amount of SCf2.

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,... 

BET area Kg-1) H2 temperature-programmed reduction (25-500° C) p.molH2g1 N2 (N20) formed (mmolg-1) ... 

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 pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

Temperature programmed reduction (TPR) experiments. TPRs were performed for each material using a quartz reactor tube (4 mm i d ), in which a 100 mg sample was mounted on loosely packed quartz wool. Samples were predried overnight at 120 °C. The sample was heated at 5 °C /min up to 700 °C under 20 mL/min flow of a 2 1 mixture of H2 Ar. 

N2-BET analysis and porosity measurements were done on a Micrometries ASAP 2000 apparatus at liquid nitrogen temperature. Temperature-programmed desorption of ammonia (NH3-TPD) and temperature-programmed reduction by H2 (H2-TPR) were performed with a Micromeritics AutoChem 2910 apparatus. 

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