{"id":5177,"date":"2024-08-27T13:51:51","date_gmt":"2024-08-27T13:51:51","guid":{"rendered":"http:\/\/121.199.166.88\/?post_type=resources&p=5177"},"modified":"2024-12-06T21:06:34","modified_gmt":"2024-12-06T21:06:34","slug":"temperature-programmed-reduction-using-the-autochem","status":"publish","type":"resources","link":"https:\/\/micromeritics.com.cn\/en\/resources\/temperature-programmed-reduction-using-the-autochem\/","title":{"rendered":"Temperature Programmed Reduction Using the AutoChem"},"content":{"rendered":"\n

Temperature-programmed reduction (TPR) is a widely used tool for the characterization of metal oxides, mixed metal oxides, and metal oxides dispersed on a support. The TPR method yields quantitative information of the reducibility of the oxide\u2019s surface, as well as the heterogeneity of the reducible surface. TPR is a method in which a reducing gas mixture (typically 3% to 17% hydrogen diluted in argon or nitrogen) flows over the sample. A thermal conductivity detector (TCD) is used to measure changes in the thermal conductivity of the gas stream. The TCD signal is then converted to concentration of active gas using a level calibration. Integrating the area under the concentration vs. time (or temperature) yields total gas consumed.<\/p>\n\n\n\n

Figure 1 shows a TPR profile for the reaction; Mx<\/sub>Oy<\/sub> + yH2<\/sub> \u2192 xM + yH2<\/sub>O where Mx<\/sub>Oy<\/sub> is a metal oxide. This figure illustrates a TPR spectrum where the peak maximum indicates the temperature that corresponds to the maximum rate of reduction. The TPR method provides a qualitative, and sometimes quantitative, picture of the reproducibility of the catalyst surface, as well as its high sensitivity to chemical changes resulting from promoters or metal\/support interactions.<\/p>\n\n\n

\n
\"Temperature-programmed
Figure 1. Temperature-programmed reduction profile for a metal
oxide. Trace A displays the TCD signal output as a function of time.
Trace B displays the temperature as a function of time during a 10 \u00b0C
heating rate from ambient to 400 \u00b0C.<\/figcaption><\/figure>\n<\/div>\n\n\n

Therefore, the TPR method is also suitable for quality control of different catalyst charges since deviations in manufacturing methods often result in different reduction profiles. Figure 2 illustrates a TPR profile for a reagent grade silver oxide (AgO) sieved to a minus 325 mesh. These data were generated using the AutoChem and show the recorded thermal conductivity signal as a function of the temperature. The specific reaction is AgO + H2<\/sub> \u2192 Ag + H2<\/sub>O. Thirty-six analyses of this particular batch of silver oxide were performed using two different AutoChems. For these 36 analyses, the average Tmax<\/sub> and H2<\/sub> consumed were:<\/p>\n\n\n\n

<\/td>Average<\/td>Sigma<\/td><\/tr>
Tmax<\/sub><\/td>119.43 \u00b0C<\/td>7.23<\/td><\/tr>
H2<\/sub> consumed<\/td>95.39 cc\/STP<\/td>1.47 cc\/STP<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The theoretical hydrogen consumption for this reaction is 96.72 cc of hydrogen at STP. Thus, the experimental H2<\/sub> consumption as measured in this series of experiments was 99.7% of theoretical. TPR ultimately yields a bulk reduction of the sample; the peak maxima are an indication of the reducibility of the metal oxide phase. Careful observation of Figure 2 shows a small, broad peak at higher temperatures than Tmax<\/sub>. This peak is attributable to the reduction of some bulk oxide in the sample. The specific particle size of the sample is an important experimental variable; in fact, for bulk oxides an increase in Tmax is predicted for an increasing particle size. TPR results are greatly influenced by 1) the programmed heating rate, 2) H2<\/sub> concentration in the flowing gas stream, and 3) the flow rate of the gas itself. For example, as the heating is increased, Tmax<\/sub> would also increase. Decreasing the hydrogen concentration in the flowing gas or decreasing the flow rate of the reducing gas would also increase Tmax<\/sub>. Therefore, precise control over these experimental variables, as is available in the AutoChem, is required when attempting to compare data taken in different laboratories.<\/p>\n\n\n

\n
\"Temperature
Figure 2. Temperature-programmed reduction profile of silver oxide.
The TCD signal is shown as a function of temperature.<\/figcaption><\/figure>\n<\/div>\n\n\n

One of the most significant advantages of temperature-programmed methods such as TPR, is that they are very sensitive probes of oxidic surfaces such as supported catalysts. Temperature-programmed methods are some of the best and quickest methods to fingerprint a metal oxide or a supported metal catalyst, and have become extremely valuable and economic methods for catalyst characterization. TPR, in particular, is a very sensitive characterization technique for determining the condition of a catalyst, particularly when using a new catalyst preparation or modifying a catalyst. The structural sensitivity of the TPR method is illustrated in Figure 3. This is the recorded spectrum for the reduction of a binary-mixed metal oxide catalyst of copper and manganese. The profile was obtained with 10% H2<\/sub> in argon flowing at 50 sccm with a linear heating rate of 10 \u00b0C per minute. The four peak areas were obtained by a simple valley-to-baseline integration; the volume of hydrogen consumed was calculated by a TCD concentration previously obtained.<\/p>\n\n\n

\n
\"Temperature
Figure 3. Temperature-programmed reduction profile of mixed copper
manganese oxide catalyst. The trace displays the TCD signal as a
function of temperature.<\/figcaption><\/figure>\n<\/div>","protected":false},"excerpt":{"rendered":"

Temperature-programmed reduction (TPR) is a widely used tool for the characterization of metal oxides, mixed metal oxides, and metal oxides dispersed on a support. The TPR method yields quantitative information of the reducibility of the oxide\u2019s surface, as well as the heterogeneity of the reducible surface. TPR is a method in which a reducing gas […]<\/p>\n","protected":false},"featured_media":0,"parent":0,"template":"","meta":{"_acf_changed":true},"methods":[25],"resource_type":[8],"class_list":["post-5177","resources","type-resources","status-publish","hentry","methods-chemisorption","resource_type-application-notes"],"acf":[],"_links":{"self":[{"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/resources\/5177","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/resources"}],"about":[{"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/types\/resources"}],"wp:attachment":[{"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/media?parent=5177"}],"wp:term":[{"taxonomy":"methods","embeddable":true,"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/methods?post=5177"},{"taxonomy":"resource_type","embeddable":true,"href":"https:\/\/micromeritics.com.cn\/en\/wp-json\/wp\/v2\/resource_type?post=5177"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}