A Model for the Temperature-Programmed Reduction of Low and High Surface Area Ceria

2000 ◽  
Vol 193 (2) ◽  
pp. 273-282 ◽  
Author(s):  
Francesca Giordano ◽  
Alessandro Trovarelli ◽  
Carla de Leitenburg ◽  
Massimiliano Giona
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Temperature Programmed Reduction ◽  
Temperature Programmed

scholarly journals Design and stabilisation of a high area iron molybdate surface for the selective oxidation of methanol to formaldehyde

2016 ◽  
Vol 188 ◽  
pp. 115-129 ◽  
Author(s):  
Stephanie Chapman ◽  
Catherine Brookes ◽  
Michael Bowker ◽  
Emma K. Gibson ◽  
Peter P. Wells
Keyword(s):  
Surface Area ◽  
Selective Oxidation ◽  
High Surface ◽  
High Surface Area ◽  
Fold Increase ◽  
Catalytic Performance ◽  
Iron Molybdate ◽  
Oxidation Of Methanol ◽  
Bulk Catalyst ◽  
Temperature Programmed

The performance of Mo-enriched, bulk ferric molybdate, employed commercially for the industrially important reaction of the selective oxidation of methanol to formaldehyde, is limited by a low surface area, typically 5–8 m2 g−1. Recent advances in the understanding of the iron molybdate catalyst have focused on the study of MoOx@Fe2O3 (MoOx shell, Fe2O3 core) systems, where only a few overlayers of Mo are present on the surface. This method of preparing MoOx@Fe2O3 catalysts was shown to support an iron molybdate surface of higher surface area than the industrially-favoured bulk phase. In this research, a MoOx@Fe2O3 catalyst of even higher surface area was stabilised by modifying a haematite support containing 5 wt% Al dopant. The addition of Al was an important factor for stabilising the haematite surface area and resulted in an iron molybdate surface area of ∼35 m2 g−1, around a 5 fold increase on the bulk catalyst. XPS confirmed Mo surface-enrichment, whilst Mo XANES resolved an amorphous MoOx surface monolayer supported on a sublayer of Fe2(MoO4)3 that became increasingly extensive with initial Mo surface loading. The high surface area MoOx@Fe2O3 catalyst proved amenable to bulk characterisation techniques; contributions from Fe2(MoO4)3 were detectable by Raman, XAFS, ATR-IR and XRD spectroscopies. The temperature-programmed pulsed flow reaction of methanol showed that this novel, high surface area catalyst (3ML-HSA) outperformed the undoped analogue (3ML-ISA), and a peak yield of 94% formaldehyde was obtained at ∼40 °C below that for the bulk Fe2(MoO4)3 phase. This work demonstrates how core–shell, multi-component oxides offer new routes for improving catalytic performance and understanding catalytic activity.

The dissociative adsorption of hydrogen sulfide over nanophase titanium dioxide

1992 ◽  
Vol 7 (10) ◽  
pp. 2840-2845 ◽  
Author(s):  
Donald D. Beck ◽  
Richard W. Siegel
Keyword(s):  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
High Surface ◽  
High Surface Area ◽  
Synthesis Method ◽  
Dissociative Adsorption ◽  
Initial Activity ◽  
Adsorption Activity ◽  
Rutile Structure ◽  
Temperature Programmed

A variety of TiO2 materials, including a nanophase TiO2 powder, were evaluated for their ability to dissociatively adsorb H2S in a H2 environment. A temperature programmed desorption technique was used to determine the rate of sulfide accumulation on the surface of the samples as a measurement of initial activity. The initial activity for the gas condensation-produced nanophase TiO2 with its rutile structure was found to be greater than that for other samples of TiO2 tested. When normalized for surface area, the initial specific activities of the rutile samples studied for the dissociative adsorption of H2S were similar in magnitude, but significantly higher than those of the anatase TiO2 samples investigated. Thus, the improvement in the activity is attributed mainly to the ability of the nanophase synthesis method to produce high surface area rutile TiO2. When evaluated using x-ray photoelectron spectroscopy, the nanophase TiO2 was found to be significantly deficient in oxygen. Annealing this material in oxygen decreased the number of anion vacancies and lowered the activity. Thus, we conclude that oxygen vacancies also contribute to the H2S dissociative adsorption activity.

Hydrogen production by ammonia decomposition using high surface area Mo2N and Co3Mo3N catalysts

2016 ◽  
Vol 6 (5) ◽  
pp. 1496-1506 ◽  
Author(s):  
Seetharamulu Podila ◽  
Sharif F. Zaman ◽  
Hafedh Driss ◽  
Yahia A. Alhamed ◽  
Abdulrahim A. Al-Zahrani ◽  
...  
Keyword(s):  
Citric Acid ◽  
Hydrogen Production ◽  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Ammonia Decomposition ◽  
Molybdenum Nitride ◽  
Ammonium Heptamolybdate ◽  
Temperature Programmed

High surface area bulk molybdenum nitride catalysts were synthesized via temperature-programmed ammonolysis of an ammonium heptamolybdate and citric acid (CA) composite.

scholarly journals Characteristics of High Surface Area Molybdenum Nitride and Its Activity for the Catalytic Decomposition of Ammonia

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 192
Author(s):  
Seo-Hyeon Baek ◽  
Kyunghee Yun ◽  
Dong-Chang Kang ◽  
Hyejin An ◽  
Min Bum Park ◽  
...  
Keyword(s):  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
High Surface ◽  
High Surface Area ◽  
Catalytic Decomposition ◽  
Molybdenum Nitride ◽  
X Ray ◽  
Temperature Programmed Oxidation ◽  
Oxidation Reduction ◽  
Temperature Programmed

High surface area (>170 m2 g−1) molybdenum nitride was prepared by the temperature-programmed nitridation of α-MoO3 with pure ammonia. The process was optimized by adjusting the experimental variables: the reaction temperature, heating rate, and molar flow rate of ammonia. The physicochemical properties of the as-formed molybdenum nitride were characterized by X-ray diffraction, N2 sorption, transmission electron microscopy, temperature-programmed oxidation/reduction, and X-ray photoelectron spectroscopy. Of the experimental variables, the nitridation temperature was found to be the most critical parameter determining the surface area of the molybdenum nitride. When the prepared molybdenum nitride was exposed to air, the specific surface area rapidly decreased because of the partial oxidation of molybdenum nitride to molybdenum oxynitride. However, the surface area recovered to 90% the initial value after H2 treatment. The catalyst with the highest degree of nitridation showed the best catalytic activity, superior to that of unmodified α-MoO3, for the decomposition of ammonia because of its high surface area.

Structure Effects of High Surface Area Molybdenum Nitride Powders, Macrocrystals and Nanoparticles as Catalysts for Thiophene Desulfurization

1998 ◽  
Vol 549 ◽  
Author(s):  
K. L. Roberts ◽  
E. J. Markel
Keyword(s):  
Surface Area ◽  
Specific Activity ◽  
High Surface ◽  
High Surface Area ◽  
Lower Surface ◽  
Metal Catalysts ◽  
Molybdenum Nitride ◽  
Temperature Programmed ◽  
Thiophene Hds ◽  
N Powder

AbstractMo2N powder, macrocrystals and nanoparticles and porous Mo metal were synthesized using temperature programmed reduction of MoO3 powder and crystals with reactant feed gases consisting of NH3 N2/H2 mixtures and pure H2. The Mo-based catalysts were characterized using BET, XRD, TGA, SEM, and STM. The Mo-based catalysts were also analyzed for the hydrodesulfurization (HDS) of thiophene. The relatively lower surface area Mo2N macrocrystalline catalysts (SSA = 44 m2/g) have a greater area specific activity than that of the higher surface area Mo2N powder catalysts (SSA = 150 m2/g) for the HDS of thiophene. Mo metal catalysts have significantly lower activity for thiophene HDS than Mo 2N catalysts and the HDS selectivities of non-sulfided Mo metal catalysts are significantly different from those of Mo 2N catalysts.

scholarly journals Synthesis, characterization, and reactivity of tungsten oxynitride

1998 ◽  
Vol 13 (8) ◽  
pp. 2321-2327 ◽  
Author(s):  
Toby E. Lucy ◽  
Todd P. St. Clair ◽  
S. Ted Oyama
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
X Ray Diffraction ◽  
Heating Rates ◽  
Continuous Transformation ◽  
X Ray ◽  
Synthesis Conditions ◽  
Temperature Programmed ◽  
Temperature Programmed Reaction

High surface area tungsten oxynitride has been prepared by the temperature programmed reaction (TPR) of WO3 with NH3. All samples were characterized by x-ray diffraction (XRD), nitrogen physisorption, CO chemisorption, and elemental analysis. Samples were prepared at different heating rates (β), and a Redhead analysis yielded an activation energy for nitridation of 109 kJ mol−1. A heating rate of 0.016 K s−1 gave optimal synthesis conditions. Solid state intermediates were studied by interrupting the temperature program at various stages. No distinct suboxide phases were found using XRD. The nitridation step was determined to be a continuous transformation from oxide to oxynitride. Surface area, CO uptake, and nitrogen weight % were all found to increase as the reaction progressed. Reactivity experiments showed reasonable hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) activity, but little hydrogenation (HYD) or hydrodesulfurization (HDS) activity.

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

2019 ◽  
Author(s):  
Kailun Yang ◽  
Recep Kas ◽  
Wilson A. Smith
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Catalyst Layer ◽  
Active Surface ◽  
Active Surface Area ◽  
High Concentration ◽  
Copper Electrodes ◽  
Surface Enhanced ◽  
Local Current

<p>This study evaluated the performance of the commonly used strong buffer electrolytes, i.e. phosphate buffers, during CO<sub>2</sub> electroreduction in neutral pH conditions by using in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Unfortunately, the buffers break down a lot faster than anticipated which has serious implications on many studies in the literature such as selectivity and kinetic analysis of the electrocatalysts. Increasing electrolyte concentration, surprisingly, did not extend the potential window of the phosphate buffers due to dramatic increase in hydrogen evolution reaction. Even high concentration phosphate buffers (1 M) break down within the potentials (-1 V vs RHE) where hydrocarbons are formed on copper electrodes. We have extended the discussion to high surface area electrodes by evaluating electrodes composed of copper nanowires. We would like highlight that it is not possible to cope with high local current densities on these high surface area electrodes by using high buffer capacity solutions and the CO<sub>2</sub> electrocatalysts are needed to be evaluated by casting thin nanoparticle films onto inert substrates as commonly employed in fuel cell reactions and up to now scarcely employed in CO<sub>2</sub> electroreduction. In addition, we underscore that normalization of the electrocatalytic activity to the electrochemical active surface area is not the ultimate solution due to concentration gradient along the catalyst layer.This will “underestimate” the activity of high surface electrocatalyst and the degree of underestimation will depend on the thickness, porosity and morphology of the catalyst layer. </p> <p> </p>

scholarly journals Rugae-like FeP nanocrystal assembly on a carbon cloth: an exceptionally efficient and stable cathode for hydrogen evolution

Nanoscale ◽  
2015 ◽  
Vol 7 (25) ◽  
pp. 10974-10981 ◽  
Author(s):  
Xiulin Yang ◽  
Ang-Yu Lu ◽  
Yihan Zhu ◽  
Shixiong Min ◽  
Mohamed Nejib Hedhili ◽  
...  
Keyword(s):  
Gas Phase ◽  
Surface Area ◽  
Hydrogen Evolution ◽  
Hydrogen Generation ◽  
High Surface ◽  
High Surface Area ◽  
Catalytic Efficiency ◽  
Carbon Cloth ◽  
Nanocrystal Assembly

High surface area FeP nanosheets on a carbon cloth were prepared by gas phase phosphidation of electroplated FeOOH, which exhibit exceptionally high catalytic efficiency and stability for hydrogen generation.

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