Comparative study of acid-basic properties of MCF impregnated with niobium and cerium species

Stawicka, Katarzyna; Decyk, Piotr; Wojtaszek-Gurdak, Anna; Ziółek, Maria

doi:10.1016/j.cattod.2018.05.025

Cited by 12 publications

(13 citation statements)

References 40 publications

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“…Heating at 100 • C did not change the spectrum, whereas heating at 200 • C led to some decrease in intensity of the band coming from the bridging bidentate nitrate species and the appearance of a new band at 1716 cm −1 . This band became very intensive after heating at 300 • C. On the basis of literature data [28,32] this band was assigned to dinitrosyl complex (Nb(NO) 2 ) formed by partial desorption of NO from the bidentate nitrate complex and NO adsorption on niobium cations in Nb 2 O 5 in combination with adsorption of NO from the gas phase. Adsorption of NO on niobium cations (LAS) only after heating at 200 • C and 300 • C indicates a very weak Lewis acidity of niobium(V) oxide loaded on SBA-15.…”

Section: A) B)mentioning

confidence: 88%

“…The former can be assigned to the bridging bidentate nitrate (Nb-O) 2 =NO [32] formed in the interaction of two neighboring metal-oxygen species in Nb 2 O 5 crystals with NO molecule. This band is accompanied by another one at 1450 cm −1 coming from ν(N=O)vibration in monodentate nitrito species (NbO-NO) [28,32]. Heating at 100 • C did not change the spectrum, whereas heating at 200 • C led to some decrease in intensity of the band coming from the bridging bidentate nitrate species and the appearance of a new band at 1716 cm −1 .…”

Section: A) B)mentioning

confidence: 95%

“…The surface acid-base properties of all materials were tested by FTIR spectroscopy measurements after pyridine and nitrogen(II) oxide adsorption. Pyridine adsorption allowed the estimation of Lewis and Brønsted acidity [27], whereas NO adsorption provided the information on the Lewis acid-base properties [28].…”

Section: Acid-base Propertiesmentioning

confidence: 99%

“…Moreover, if strong Lewis base species are present on the surface of a solid, NO molecule can be chemisorbed on them forming nitrito or nitrato ions. Nitrogen(II) oxide has been used for identification of niobium species incorporated to silica matrix, namely niobium cations (Lewis acid sites) and NbO − species playing a role of base/redox centers (e.g., [28,31,33,34]). The FTIR spectra of niobium containing SBA-15 materials after adsorption of NO at room temperature (r.t.), followed by heating at 100 • C, 200 • C and 300 • C, are shown in Figure 5.…”

Section: A) B)mentioning

confidence: 99%

“…This band became very intensive after heating at 300 °C. On the basis of literature data [28,32] this band was assigned to dinitrosyl complex (Nb(NO)2) formed by partial desorption of NO from the bidentate nitrate complex and NO adsorption on niobium cations in Nb2O5 in combination with adsorption of NO from the gas phase. Adsorption of NO on niobium cations (LAS) only after heating at 200 °C and 300 °C indicates a very weak Lewis acidity of niobium(V) oxide loaded on SBA-15.…”

Section: A) B)mentioning

confidence: 99%

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Insight into Active Centers and Anti-Coke Behavior of Niobium-Containing SBA-15 for Glycerol Dehydration

Stawicka¹,

Trejda²,

Ziółek³

2021

Catalysts

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Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).

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Section: A) B)mentioning

confidence: 88%