Solid state NMR and IR studies of phosphomolybdenum and phosphotungsten heteropoly acids supported on SiO2, $gamma;-Al2O3, and SiO2$z.sbnd;Al2O3

Rao, K. Mallikarjuna; Gobetto, Roberto; Iannibello, A.; Zecchina, Adriano

doi:10.1016/0021-9517(89)90179-6

Cited by 99 publications

(9 citation statements)

References 7 publications

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“…The IR spectra of the different loadings of PWA on silica calcined at 350 • C indicates that most of the characteristic bands of the parent Keggin structure can be found in the PWA fingerprint region (1250-500 cm −1 ), not shown, or appearing in the same assignable position of the bands corresponding to the SiO 2 host material. In comparison with the IR results reported by Mohana Rao et al 26 and Nowinska et al 27 neither a systematic shift nor a weak band at 925 cm −1 , which may result from the higher calcination temperature, could be found for silica supported PWA samples with different loadings.…”

Section: Catalytic Activity Measurementscontrasting

confidence: 68%

Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

Said¹,

El‐Wahab²,

Alian³

2007

J of Chemical Tech & Biotech

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Different ratios of phosphotungestic acid supported on silica gel were prepared by an impregnation method with PWA loadings ranging from 1 to 30% w/w and calcined at 350 and 500 • C for 4 h in a static air atmosphere. The catalysts were characterized by thermogravimety (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N 2 adsorption measurements. The surface acidity and basicity of the catalyst were investigated by the dehydration-dehydrogenation of isopropanol and the adsorption of pyridine (PY) and 2,6-dimethyl pyridine (DMPY). The gas-phase estrification of acetic acid with ethanol was carried out at 185 • C in a conventional fixed-bed reactor at 1 atm using air as carrier gas. The results clearly revealed that the catalyst containing 10% w/w PWA/SiO 2 is the most active and delivers reaction selectively to ester with 85% yield. The Brønsted acid site resulting from hydroxylation of tungsten oxide plays the main role in the formation of ester. Figure 1 shows TG and DTA curves of the pure silica, pure PWA and PWA supported on silica. It is seen 514 Perspective Perspective 55 Sheinthauer M, Cheung TK, Jentoft RE, Grasselli RK, Gates BC and Knozinger H, Characterization of WO x /ZrO 2 by vibrational spectroscopy and n-Pentane isomerization catalysis. J Catal 180:1-13 (1998). 56 Baertsch CD, Soled SL and Iglesia E, Isotopic and chemical titration of acid sites in tungsten oxide domains supported on zirconia. J Phys Chem B 105:1320-1330 (2001). RESULTS AND DISCUSSION Thermal analysis

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Section: Catalytic Activity Measurementscontrasting

confidence: 68%

Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

Said¹,

El‐Wahab²,

Alian³

2007

J of Chemical Tech & Biotech

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“…These supports are found to be suitable as they can preserve the Keggin ion up to higher temperatures [14]. A number of researchers have focused attention on the thermal stability of HPAs by supporting them on various acidic or basic substrates [5,[15][16][17][18][19]. In recent years much attention has been focused on the amphoteric zirconium dioxide (ZrO 2 ) as an outstanding catalyst and catalyst support.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Zirconia Supported Vanadium Incorporated Ammonium Salt of 12-molybdophosphoric Acid Catalyst for Aerobic Oxidation of Benzyl alcohol

et al. 2007

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A series of zirconia supported ammonium salt of molybdophosphoric acid (AMPV) catalysts with and with out vanadium incorporation are prepared in a single step adopting wet impregnation method. These catalysts are characterized by BET surface area, XRD, FT-IR and potentiometric titration. XRD and FT-IR techniques suggest the formation of Keggin ion on zirconia support. The high resolution FT-IR analysis reveals the incorporation of vanadium into the primary structure of Keggin ion. The catalytic functionalities of these catalysts are tested for the aerobic oxidation of benzyl alcohol. The vanadium containing AMPV results in higher selectivity towards the oxidation product compared to the catalyst without vanadium incorporation.

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“…Sin embargo, es aconsejable soportarlos, ya que presentan muy bajos valores de superficie específica (3-5 m 2 /g), lo que limita considerablemente su desempeño como catalizadores heterogéneos. Para superar esta desventaja, los KHPA se soportan sobre diferente tipo de sólidos porosos (sílice, circonia, alúmina o carbono, entre otros) [17,18]. Entre estos, se ha encontrado que los KHPA son más estables cuando el soporte es sílice ya que se genera unainteracción electrostática entre el heteropoliácido y el soporte, a través de la protonación de los grupos hidroxilo superficiales de este último [19][20][21].…”

Section: Introductionunclassified

Nanoestructuras de sílice, con diámetro y distribución de mesoporos variable, modificadas con ácido tungstofosfórico como catalizadores en la síntesis de quinoxalinas

2020

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Se sintetizaron catalizadores (SNX#WPA) basados en ácido tungstofosfórico, en soportes de nanoestructuras de sílice (SNX), con distribución de diámetros y tamaños de mesoporos variables. Las SNX se prepararon en medio de octano/agua, usando poliestireno y bromuro de cetiltrimetilamonio como plantillas. Los materiales se caracterizaron por DRX, TEM y adsorción/desorción de nitrógeno. La relación octano/agua influyó tanto en la morfología y el tamaño de las SNX como en la distribución del tamaño de poro. Las SNX obtenidas utilizando relaciones OCT/H2O en el rango de 0,07-0,35, presentan mesoporos pequeños (5-6 nm) y grandes (28-34 nm), generados principalmente por poliestireno. Los mesoporos grandes y su contribución de volumen fueron claramente más altos que en las muestras SN1, SN2 y SN3. La estructura y la morfología de SNX#WPA fueron similares a las de las SNX usadas como soporte. Además, la caracterización de todos los materiales SNX#WPA por FT-IR y 31P NMR indicó la presencia de especies [PW12O40]3− y [H3-XPW12O40](3-X)− sin degradar. Según los resultados de la valoración potenciométrica, los sólidos presentaron sitios ácidos muy fuertes. Se evaluó la actividad de SNX#WPA como catalizadores en la síntesis de quinoxalinas, a partir de lo cual se obtuvieron altos rendimientos, sin formación de subproductos. De ello resultó que los materiales preparados son catalizadores altamente selectivos y reutilizables.

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Solid state NMR and IR studies of phosphomolybdenum and phosphotungsten heteropoly acids supported on SiO2, $gamma;-Al2O3, and SiO2$z.sbnd;Al2O3

Cited by 99 publications

References 7 publications

Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

Synthesis and Characterization of Zirconia Supported Vanadium Incorporated Ammonium Salt of 12-molybdophosphoric Acid Catalyst for Aerobic Oxidation of Benzyl alcohol

Nanoestructuras de sílice, con diámetro y distribución de mesoporos variable, modificadas con ácido tungstofosfórico como catalizadores en la síntesis de quinoxalinas

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