Temperature-programmed reduction (TPR) is a technique for the characterization of solid materials and is often used in the field of heterogeneous
catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
to find the most efficient
reduction conditions, an oxidized catalyst precursor is submitted to a programmed temperature rise while a reducing gas mixture is flowed over it. It was developed by John Ward Jenkins whilst developing
heterogeneous catalysts
In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phas ...
for
Shell Oil company
Shell USA, Inc. (formerly Shell Oil Company, Inc.) is the United States-based wholly owned subsidiary of Shell plc, a UK-based transnational corporation " oil major" which is amongst the largest oil companies in the world. Approximately 18,0 ...
, but was never patented.
Process description
A simple container (U-tube) is filled with a solid or catalyst. This sample vessel is positioned in a furnace with temperature control equipment. A
thermocouple
A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of th ...
is placed in the solid for temperature measurement. The air originally present in the container is flushed out with an
inert gas
An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
(
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
). Flow controllers are used to add hydrogen (for example, 10% hydrogen in nitrogen). The composition of the gaseous mixture is measured at the exit of the sample container with appropriate detectors (
thermal conductivity detector The thermal conductivity detector (TCD), also known as a katharometer, is a bulk property detector and a chemical specific detector commonly used in gas chromatography. This detector senses changes in the thermal conductivity of the column eluent an ...
,
mass spectrometer
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is us ...
). Now, the sample in the oven is heated up on predefined values. Heating rates are usually between 1 K/min and 20 K/min. If a reduction takes place at a certain temperature, hydrogen is consumed, which is recorded by the detector. In practice the production of water is a more accurate way of measuring the reduction. This is due to the potential for varying hydrogen concentrations at the inlet, so the decrease in this number may not be precise, however as the starting concentration of water will be zero, any increase can be measured more accurately.
See also
*
Thermal desorption spectroscopy Temperature programmed desorption (TPD) is the method of observing desorbed molecules from a surface when the surface temperature is increased. When experiments are performed using well-defined surfaces of single-crystalline samples in a continuousl ...
References
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External links
Temperature-programmed reduction and oxidation experiments with V2O5 catalystsHigh-Pressure Temperature-Programmed Reduction of Sulfided CatalystsLecture slides on Temperature Programmed Reduction and Oxidation
Hydrogen technologies
Analytical chemistry
Materials science
Surface science
Catalysis