A study of the dispersion of molybdenum(VI) supported on silica and .gamma.-alumina

Rodrigo, L.; Marcinkowska, K.; Adnot, A.; Roberge, Pierre C.; Kaliaguine, Serge; Stencel, J.M.; Makovsky, Leo E.; Diehl, J. Rodney

doi:10.1021/j100403a027

Cited by 50 publications

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“…The O 2 adsorption stoichiometry was assumed to be ½ O 2 /Ag = 1 (as used by Vannice) to give a Ag dispersion of 0.95%, corresponding to an average Ag diameter of 0.12 lm. Titration with O 2 for samples containing Cs, Re, and Mo was not performed because Cs [25], Re [47], and Mo [48] might interact with O 2 , which would skew the results and make accurate calculations of the average Ag particle sizes unreliable.…”

Section: Catalyst Characterizationmentioning

confidence: 99%

An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

Diao

DiGiulio

Schaal

et al. 2015

Journal of Catalysis

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Section: Catalyst Characterizationmentioning

confidence: 99%

An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

Diao

DiGiulio

Schaal

et al. 2015

Journal of Catalysis

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“…The oxygen chemisorption amounts obtained here represent irreversible uptakes by the samples, as indicated by the lack of a desorption tail at the end of each pulse and these amounts are doubled to obtain atomic oxygen uptake values. Previous studies, 19,20 used T red = 773 K and T ads = 77 K, followed by evacuation and readsorption at 195 K. These conditions were evaluated by Rodrigo et al 21 who concluded that O 2 chemisorption under these conditions does not provide a quantitative determination of Mo dispersion because a fraction of the reduced Mo is in the bulk. It has been shown that oxygen chemisorption sites are easily generated under very mild reduction conditions, such as those employed in this study.…”

Section: Green Contextmentioning

confidence: 99%

“…Prior to TPD studies the catalyst sample was pretreated by passing high purity helium (50 ml min 21 ) at 473 K for 2 h. After pretreatment, the sample was saturated by passing (75 ml min 21 ) 10% NH 3 -He at 353 K, and subsequently flushing at 378 K for 2 h to remove the physisorbed ammonia. TPD analysis was carried out from ambient temperature to 1073 K at a heating rate of 10 K min 21 . The NH 3 uptake amounts were calculated using GRAMS/32 software.…”

Section: Temperature-programmed Desorption (Tpd) Of Nhmentioning

confidence: 99%

Dispersion and reactivity of Mo/Nb2O5 catalysts in the ammoxidation of toluene to benzonitrile

et al. 2002

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A series of Mo/Nb 2 O 5 catalysts were prepared with Mo loadings ranging from 2.5-15 wt% of Mo and characterized by X-ray diffraction (XRD), pulse oxygen chemisorption, temperature-programmed desoprtion of ammonia. Dispersion of molybdena was determined by oxygen chemisorption at 623 K in a dynamic method. At low Mo loadings molybdenum oxide is found to be present in a highly dispersed state. XRD results show the presence of crystalline MoO 3 at higher Mo loadings (from 10 wt%). The dispersion of molybdena was found to decrease with increased Mo loading due to formation of MoO 3 . The catalytic properties were evaluated for the vapour phase ammoxidation of toluene to benzonitrile and are related to different characterization results.

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“…(36,37) At low loadings a larger quantity of the silicomolybdic species was present in the catalysts prepared from the ammonium paramolybdate.…”

Section: Regeneration In the Presence Of Watermentioning

confidence: 99%

Stability

2002

Metal-Oxygen Clusters

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A large number of publications have reported studies of the thermal stability of heteropoly oxometalates as part of investigations of other aspects of these materials. Although these reports may have been discussed elsewhere in this monograph where relevant, they have also been included here. The present discussion of thermal stability is, for convenience, restricted to unsupported heteropoly oxometalates with that pertaining to the supported materials included in the section on the properties of the latter. A cautionary note should be added here. The results from studies of stability are dependent not only on the method employed for such evaluations, but in addition are frequently dependent on the conditions under which the experiment was performed.One of the earliest studies of the stability of the heteropoly acids employed differential thermal analysis and X-ray diffraction. (1) With each of the four acids examined, an endotherm and an exotherm are observed at 300 C or less and 340 C or more, respectively (Table 5.1). The low-temperature endotherm is attributed to the removal of water whereas the high-temperature exotherm signals the decomposition of the anion. The authors note that metatungstic acid H 8 [W 12 O 40 ]ÁxH 2 O decomposes at 50 C. When the void in the center of the [W 12 O 40 ] 8À anion is occupied by Si 4 or P 5 , the decomposition temperature increases by approximately 400 or 500 C, respectively. The presence of a positively charged species reduces the effect of thermal vibrations and thus of decomposition.Thermogravimetric analyses of H 3 XW 12 O 40 with X being zinc, iron, cobalt, boron, silicon, or phosphorus, their potassium salts, and their ether-addition compounds have been reported. (2) With the ®rst three acids, three peaks were observed whereas only two were obtained with the latter three acids (Table 5.2). The third peak was attributed to decomposition of the anion. 42CHAPTER 5 STABILITY 43

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A study of the dispersion of molybdenum(VI) supported on silica and .gamma.-alumina

Cited by 50 publications

References 0 publications

An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

Dispersion and reactivity of Mo/Nb2O5 catalysts in the ammoxidation of toluene to benzonitrile

Stability

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