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Temperature-programmed reduction

About: Temperature-programmed reduction is a(n) research topic. Over the lifetime, 2924 publication(s) have been published within this topic receiving 97092 citation(s).
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Journal ArticleDOI
Abstract: Temperature programmed reduction (TPR) and hydrogen chemisorption combined with reoxidation measurements were used to define the reducibility of supported cobalt catalysts. Different supports (e.g. Al2O3, TiO2, SiO2, and ZrO2 modified SiO2 or Al2O3) and a variety of promoters, including noble metals and metal cations, were examined. Significant support interactions on the reduction of cobalt oxide species were observed in the order Al2O3>TiO2>SiO2. Addition of Ru and Pt exhibited a similar catalytic effect by decreasing the reduction temperature of cobalt oxide species, and for Co species where a significant surface interaction with the support was present, while Re impacted mainly the reduction of Co species interacting with the support. For catalysts reduced at the same temperature, a slight decrease in cluster size was observed in H2 chemisorption/pulse reoxidation with noble metal promotion, indicating that the promoter aided in reducing smaller Co species that interacted with the support. On the other hand, addition of non-reducible metal oxides such as B, La, Zr, and K was found to cause the reduction temperature of Co species to shift to higher temperatures, resulting in a decrease in the percentage reduction. For both Al2O3 and SiO2, modifying the support with Zr was found to enhance the dispersion. Increasing the cobalt loading, and therefore the average Co cluster size, resulted in improvements to the percentage reduction. Finally, a slurry phase impregnation method led to improvements in the reduction profile of Co/Al2O3.

737 citations

Journal ArticleDOI
Abstract: It is shown that temperature-programmed reduction (TPR) is a sensitive technique for the characterization of Co- and CoAl-oxidic phases in CoOAl2O3 catalysts. Four different reduction regions can be present for CoOAI2O3catalysts, which are assigned to four Co phases (I, II, III, and IV). Phase I (reduction at ca. 600 K in TPR at 10 K/min) consists of Co34 crystallites. Phase II (reduction at ca. 750 K) consists of Co3+ ions, in crystallites of proposed stoichiometry Co3AlO6 or in well-dispersed surface species. Phase III (reduction at ca. 900 K) consists of surface Co2+ ions. Phase IV (reduction at ca. 1150 K) consists either of surface Co2+ ions (with more Al3+ ions in their surrounding than in phase III) or of subsurface Co2+ ions, occurring in diluted Co2+Al3+ spinel structures or in CoAl2O4. Al3+ ions influence the reducibility of Co ions strongly. This is explained by polarization of CoO bonds by Al3+ ions. Preparation conditions (calcination flow rate and calcination temperature) influence the structure of CoOAl2O3, namely the Co valency, the extent of solid-state diffusion, and the dispersion. Solid-state diffusion of Co2+ and Al3+ ions occurs above ca. 800 K. The implications of this study for CoO-MoO3Al2O3 hydrodesulfurization catalysts are discussed.

600 citations

Journal ArticleDOI
Abstract: Combined in situ FTIR and on-line mass spectrometric studies have provided simultaneous information of the surface adsorbed species on vanadia/titania catalysts and the composition of reaction products during the selective catalytic reduction (SCR) of NO. The experiments were carried out as temperature programmed surface reaction (TPSR) studies by exposing catalysts with preadsorbed ammonia to either pure NO, pure O2, or a mixture of NO and O2. This allowed detailed information to be obtained concerning the changes in the concentrations and the nature of the surface VO and VOH species. The TPSR studies in O2 showed mainly ammonia desorption and some ammonia oxidation at high temperatures. The SCR reaction was observed to take place during the TPSR studies in both NO and NO + O2, but a greater rate was observed in the latter case. It was found that NH3 reduces the VO species and subsequent reaction with NO results in the formation of reduced VOH species. The results showed that the NO reduction reaction involves the ammonia species adsorbed on VOH Bronsted acid sites. Evidence for the importance of redox reactions was also found. Separate temperature programmed reduction (TPR) studies in H2 showed that the surface vanadia layer breaks up while re-exposing TiOH groups. Subsequent temperature programmed oxidation (TPO) studies in O2 showed this phenomenon to be completely reversible, thus providing direct evidence for spreading/redispersion of vanadia on titania. The TPR/TPO studies also indicated that the Bronsted acid sites essential for the deNOx reaction are associated with V5+OH surface sites.

525 citations

Journal ArticleDOI
01 Nov 2001-Catalysis Letters
Abstract: The composite system of nanostructured gold and cerium oxide, with a gold loading 5–8 wt%, is reported in this work as a very good catalyst for low-temperature water–gas shift. Activity depends largely on the presence of nanosized ceria particles. Various techniques of preparation of an active catalyst are disscussed. The presence of gold is crucial for activity below 300°C. A dramatic effect of gold on the reducibility of the surface oxygen of ceria is found by H2-TPR, from 310–480°C to 25–110°C. All of the available surface oxygen was reduced, while there was no effect on the bulk oxygen of ceria. This correlates well with the shift activity of the Au–ceria system.

515 citations

Journal ArticleDOI
Abstract: Catalytic combustion of volatile organic compounds (VOCs: benzene and toluene) was studied over manganese oxide catalysts (Mn3O4, Mn2O3 and MnO2) and over the promoted manganese oxide catalysts with alkaline metal and alkaline earth metal. Their properties and performance were characterized by using the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The sequence of catalytic activity was as follows: Mn3O4 > Mn2O3 > MnO2, which was correlated with the oxygen mobility on the catalyst. Each addition of potassium (K), calcium (Ca) and magnesium (Mg) to Mn3O4 catalyst enhanced the catalytic activity of Mn3O4 catalyst. Accordingly, K, Ca and Mg seemed to act as promoters, and the promoting effect might be ascribed to the defect-oxide or a hydroxyl-like group. A mutual inhibitory effect was observed between benzene and toluene in the binary mixture. In addition, the order of catalytic activity with respect to VOC molecules for single compound is benzene > toluene, and the binary mixture showed the opposite order of toluene > benzene.

484 citations

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Topic's top 5 most impactful authors

Mehran Rezaei

20 papers, 570 citations

Jacob A. Moulijn

18 papers, 1.6K citations

P.S. Sai Prasad

15 papers, 461 citations

Elisabete Moreira Assaf

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Fernando Cárdenas-Lizana

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