TY - JOUR

T1 - Thermodynamic properties of gaseous cerium molybdates and tungstates studied by Knudsen effusion mass spectrometry.

AU - Shugurov, S.M.

AU - Panin, A.I.

AU - Lopatin, S.I.

PY - 2018/9/30

Y1 - 2018/9/30

N2 - Rationale: CeO 2–WO 3 and CeO 2–MoO 3 catalysts have shown excellent performance in the selective reduction of NO x by ammonia (NH 3-selective catalytic reduction) over a wide temperature range. Strong interaction between CeO 2 and WO 3 or MoO 3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria-containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown. Methods: Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas-phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO 2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium molybdates and tungstates was performed by several quantum chemical methods. Results: In the temperature range 2050–2400 K, CeO, CeO 2, XO 2, XO 3, CeWO 3, CeXO 4, CeXO 5 (X = Mo, W) and CeMo 2O 7 were found to be the main vapor species over the CeO 2–Mo(W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO 3, CeXO 4, CeXO 5 (X = Mo, W) and CeMo 2O 7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation. Conclusions: The thermal stability of gaseous cerium oxyacid salts was confirmed by high-temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental ones.

AB - Rationale: CeO 2–WO 3 and CeO 2–MoO 3 catalysts have shown excellent performance in the selective reduction of NO x by ammonia (NH 3-selective catalytic reduction) over a wide temperature range. Strong interaction between CeO 2 and WO 3 or MoO 3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria-containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown. Methods: Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas-phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO 2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium molybdates and tungstates was performed by several quantum chemical methods. Results: In the temperature range 2050–2400 K, CeO, CeO 2, XO 2, XO 3, CeWO 3, CeXO 4, CeXO 5 (X = Mo, W) and CeMo 2O 7 were found to be the main vapor species over the CeO 2–Mo(W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO 3, CeXO 4, CeXO 5 (X = Mo, W) and CeMo 2O 7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation. Conclusions: The thermal stability of gaseous cerium oxyacid salts was confirmed by high-temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental ones.

UR - http://www.scopus.com/inward/record.url?scp=85051415614&partnerID=8YFLogxK

U2 - 10.1002/rcm.8210

DO - 10.1002/rcm.8210

M3 - Article

VL - 32

SP - 1608

EP - 1616

JO - Rapid Communications in Mass Spectrometry

JF - Rapid Communications in Mass Spectrometry

SN - 0951-4198

IS - 18

ER -