PROX reaction over Pt3Sn/Al2O3: Structural investigation by operando DRIFTS

International @ INGENIERIE+AMS:YSC:FRMInternational audiencePtxSn based catalysts have presented exhibit enhanced activities for preferential CO oxidation (PROX) as compared to analogous Pt catalysts. Yet, often ill-defined PtSn phases present on the catalyst prevent a full understanding of the reaction mechanism and active sites involved. Therefore we used for this study well-defined Pt and Pt3Sn catalysts, obtained by impregnation of pre-formed Pt or Pt3Sn nanoparticles [1]. Our 1% Pt3Sn/?-Al2O3 and 1% Pt/?-Al2O3 catalysts were used in the CO PROX. Experiments were carried out under controlled conditions to obtain intrinsic kinetics. Additionally an investigation of CO adsorption under the reaction mixture was carried out by operando DRIFTS over the samples. An unusual evolution of the adsorbed CO was noted while ramping up the temperature

Direct evidence of Pt-Sn alloy surface segregation at low temperatures by in situ IR of CO adsorption

National @ INGENIERIE+AMS:FRM:YSCInternational audienceIn the present study, a direct evidence of the surface segregation induced by CO adsorption on the structure of a Pt-Sn alloy supported on alumina is reported for the first time. The surface segregation was monitored by in situ diffuse reflectance FT-IR spectroscopy (DRIFTS) in a 2% CO/H2 atmosphere at various temperatures and showed to occur only below 175°C and was partly reversible following reduction at high temperature. The experiments are performed as well on a Sn-free sample for comparison and the behavior observed is typically to a Pt supported catalyst

Direct evidence of Pt-Sn alloy surface segregation at low temperatures by in situ IR of CO adsorption

National @ INGENIERIE+AMS:FRM:YSCInternational audienceIn the present study, a direct evidence of the surface segregation induced by CO adsorption on the structure of a Pt-Sn alloy supported on alumina is reported for the first time. The surface segregation was monitored by in situ diffuse reflectance FT-IR spectroscopy (DRIFTS) in a 2% CO/H2 atmosphere at various temperatures and showed to occur only below 175°C and was partly reversible following reduction at high temperature. The experiments are performed as well on a Sn-free sample for comparison and the behavior observed is typically to a Pt supported catalyst

DRIFTS of the PReferential OXidation of CO (PROX) over Pt-Sn/Al2O3: evidence of surface segregation under reaction conditions

SSCI-VIDE+ING+YSC:FRMInternational audienceNon

PROX reaction over Pt3Sn/Al2O3: Structural investigation by operando DRIFTS

International @ INGENIERIE+AMS:YSC:FRMInternational audiencePtxSn based catalysts have presented exhibit enhanced activities for preferential CO oxidation (PROX) as compared to analogous Pt catalysts. Yet, often ill-defined PtSn phases present on the catalyst prevent a full understanding of the reaction mechanism and active sites involved. Therefore we used for this study well-defined Pt and Pt3Sn catalysts, obtained by impregnation of pre-formed Pt or Pt3Sn nanoparticles [1]. Our 1% Pt3Sn/?-Al2O3 and 1% Pt/?-Al2O3 catalysts were used in the CO PROX. Experiments were carried out under controlled conditions to obtain intrinsic kinetics. Additionally an investigation of CO adsorption under the reaction mixture was carried out by operando DRIFTS over the samples. An unusual evolution of the adsorbed CO was noted while ramping up the temperature

DRIFTS of the PReferential OXidation of CO (PROX) over Pt-Sn/Al2O3: evidence of surface segregation under reaction conditions

SSCI-VIDE+ING+YSC:FRMInternational audienceNon

DRIFTS of the PReferential OXidation of CO (PROX) over Pt-Sn/Al2O3: evidence of surface segregation under reaction conditions

SSCI-VIDE+ING+YSC:FRMInternational audienceNon

Direct evidence by in situ IR CO monitoring of the formation and the surface segregation of a Pt-Sn alloy

INGENIERIE+AMS:YSC:FRMThe heat of CO adsorption on the Pt atoms of a Pt-Sn alloy phase could be specifically determined from in situ DRIFTS data and was found to be about half that measured on a plain Pt reference. Surprisingly, a reversible surface segregation of the Pt-Sn alloy was observed at temperatures below 175 degrees C

CO PROX over Pt-Sn/Al2O3: A combined kinetic and in situ DRIFTS study

SSCI-VIDE+ING+AMS:FRM:YSCInternational audiencePreferential oxidation of CO (PROX) in hydrogen-rich mixtures was studied over alumina-supported Pt and Pt-Sn catalysts, which exhibited a well-defined metal particle size. The reaction rate was much faster over Pt-Sn/Al2O3 than over Pt/Al2O3. Significantly different apparent activation energies and oxygen reaction orders were found for both samples. Whereas the CO PROX kinetics over Pt/Al2O3 could be described by oxygen adsorption as being rate-determining step, this was not the case for Pt-Sn. In situ Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) showed that Pt-Sn, initially under a mixture of 1% CO/80% H-2, segregated upon the introduction of 2% O-2, even at temperatures where the alloy was stable under reducing conditions. For the CO PROX reaction over Pt-Sn/Al2O3 a bifunctional mechanism is proposed with CO and H being adsorbed on the platinum sites and oxygen being channeled from neighboring SnOx sites. This work suggests a Mars-Van Krevelen type of mechanism for the SnOx, site, in agreement with the low value of 0.2 for the oxygen reaction order over Pt-Sn. (C) 2015 Elsevier B.V. All rights reserved

A water-based and high space-time yield synthetic route to MOF Ni-2(dhtp) and its linker 2,5-dihydroxyterephthalic acid

SSCI-VIDE+ING+SCT:DFAInternational audience2,5- Dihydroxyterephthalic acid (H(4)dhtp) was synthesized on an 189 scale by carboxylation of hydroquinone in molten potassium formate. The hydrated form of the Ni-2(dhtp) MOF (also known as CPO-27-Ni and MOF-74(Ni)) was obtained in 92% yield by refluxing for 1 h a water suspension of the H(4)dhtp linker with an aqueous solution of nickel acetate. The ensuing characterization of the material (XRD, HRTEM, TGA, N-2 adsorption at 77 K - S-BET = 1233 m(2) g(-1)) confirmed the formation of a metal-organic framework of at least equal quality to the ones obtained from the previously reported routes (CPO-27-Ni and MOF-74(Ni)), with a different morphology (namely, well-separated 1 mu m platelets for the herein reported water-based route). The temperature dependence of the magnetic susceptibility was measured and satisfactorily simulated assuming a Heisenberg (H = -2J Sigma SiSi+1) ferromagnetic intrachain interaction (J = +8.1 cm(-1)) and an antiferromagnetic interchain interaction (J' = -1.15 cm(-1)). Overall, the reaction in water appears to follow easily distinguishable steps, the first being the deprotonation of H(4)dhtp by an acetate counterion, leading to a soluble nickel adduct of the linker, en route to the MOF self-assembly