On the Role of Support in Metallic Heterogeneous Catalysis: A Study of Unsupported Nickel\u2013Cobalt Alloy Nanoparticles in Ethanol Steam Reforming

(Co, Ni) bimetallic nanoparticles have been prepared by reducing Ni and Co chloride solutions with sodium borohydride. The obtained materials have been characterized as cast and/or after annealing by means of XRD, magnetic measurements, IR spectroscopy, FE-SEM and TEM microscopies. The resulting nanomaterials, originally amorphous, crystallize into the cubic structure cF4-Cu as homogeneous (Co, Ni) solid solution alloy and with the additional presence of Boron containing phases due to the residual preparation impurities. The bimetallic nanoparticles are active in ethanol conversion in the presence of steam. For low Boron catalysts, the addition of Nickel to Cobalt nanoparticles improves the catalytic activity in ethanol steam reforming allowing yields as high as 87% at 773 K, at high space velocities (GHSV 324,000 h 121 ). The performances of the catalytic unsupported nanoparticles with a Ni/Co atomic ratio equal to 0.26 appear to be better than those of conventional supported catalysts. The state of Boron impurities affect catalytic activity of bimetallic (Co, Ni) NPs. Carbonaceous materials, such as carbon nanotubes and graphitic carbon, form on the catalyst surface upon reaction. Graphical Abstract: [Figure not available: see fulltext.]

A study of Ni/La-Al 2 O 3 catalysts: A competitive system for CO 2 methanation

Ni/La-\u3b3-Al 2 O 3 samples containing 13.6 wt.% Ni and a variable amount of lanthana (0, 4, 14 and 37 wt.%) were prepared by incipient wetness impregnation, using silica-free \u3b3-Al 2 O 3 support. The materials were characterized, as such or after reaction, with XRD, H 2 -TPR, IR, UV\u2013vis-NIR, XPS and FE-SEM techniques. They were tested as catalysts for CO 2 methanation at atmospheric pressure at GHSV 55000 h 121 . The reaction is under kinetic control at T < 650\u2013673 K, while the product mixture is under thermodynamic control above this temperature range. Lanthanum addition strongly increases the activity of Ni/\u3b3-Al 2 O 3 for CO 2 methanation. Methane selectivity is increased to nearly 100% at low temperatures (T < 650 K). The CO 2 methanation reaction on La-doped Ni/\u3b3-Al 2 O 3 occurs with similar activation energies (80 kJ/mol), and with slightly higher reaction order for hydrogen and lower reaction order for CO 2 than those observed for undoped Ni/\u3b3-Al 2 O 3 . Lanthanum acts as a promoter because of the stronger basicity of the lanthana-alumina support allowing stronger adsorption of CO 2 as surface carbonates that can be act as \u201creactant reservoirs\u201d. The Ni/La-alumina catalysts studied here are similarly effective as Ru/alumina catalysts for the selective CO 2 methanation at low temperature and atmospheric pressure

Modeling of Laboratory Steam Methane Reforming and CO2 Methanation Reactors

To support the interpretation of the experimental results obtained from two laboratory-scale reactors, one working in the steam methane reforming (SMR) mode, and the other in the CO2 hydrogenation (MCO2) mode, a steady-state pseudo-homogeneous 1D non-isothermal packed-bed reactor model is developed, embedding the classical Xu and Froment local kinetics. The laboratory reactors are operated with three different catalysts, two commercial and one homemade. The simulation model makes it possible to identify and account for thermal effects occurring inside the catalytic zone of the reactor and along the exit line. The model is intended to guide the development of small size SMR and MCO2 reactors in the context of Power-to-X (P2X) studies

Structural Effects on the C-S Bond Cleavage in Aryl tert-Butyl Sulfoxide Radical Cations

The oxidation of a series of aryl tert-butyl sulfoxides (4-X-C6H4SOC(CH3)(3): 1, X = OCH3; 2, X = CH3; 3, X = H; 4, X = Br) photosensitized by 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Products deriving from the CS bond cleavage in the radical cations 1(+center dot)-4(+center dot) have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQ(center dot) (lambda(max) = 390 nm) and 1(+center dot)-4(+center dot) (lambda(max) = 500-620 nm) was observed. A first-order decay of the sulfoxide radical cations, attributable to C-S bond cleavage, was observed with fragmentation rate constants (k(f)) that decrease by increasing the electron donating power of the arylsulfinyl substituent from 1.8 x 10(6) s(-1) (4(+center dot)) to 2.3 x 10(5) s(-1) (1(+center dot)). DFT calculations showed that a significant fraction of the charge is delocalized in the tert-butyl group of the radical cations, thus explaining the small substituent effect on the C-S bond cleavage rate constants. Via application of the Marcus equation to the kinetic data, a very large value for the reorganization energy (lambda = 62 kcal mol(-1)) has been calculated for the C-S bond scission reaction in 1(+center dot)-4(+center dot)

Structural Effects on the C–S Bond Cleavage in Aryl <i>tert</i>-Butyl Sulfoxide Radical Cations

The oxidation of a series of aryl <i>tert</i>-butyl sulfoxides (4-X-C₆H₄SOC­(CH₃)₃: <b>1</b>, X = OCH₃; <b>2</b>, X = CH₃; <b>3</b>, X = H; <b>4</b>, X = Br) photosensitized by 3-cyano-<i>N</i>-methylquinolinium perchlorate (3-CN-NMQ⁺) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Products deriving from the C–S bond cleavage in the radical cations <b>1</b>^<b>+•</b>–<b>4</b>^<b>+•</b> have been observed in the steady-state photolysis experiments. By laser irradiation, the formation of 3-CN-NMQ^• (λ_max = 390 nm) and <b>1</b>^<b>+•</b>–<b>4</b>^<b>+•</b> (λ_max = 500–620 nm) was observed. A first-order decay of the sulfoxide radical cations, attributable to C–S bond cleavage, was observed with fragmentation rate constants (<i>k</i>_f) that decrease by increasing the electron donating power of the arylsulfinyl substituent from 1.8 × 10⁶ s^–1 (<b>4</b>^+•) to 2.3 × 10⁵ s^–1 (<b>1</b>^+•). DFT calculations showed that a significant fraction of the charge is delocalized in the <i>tert</i>-butyl group of the radical cations, thus explaining the small substituent effect on the C–S bond cleavage rate constants. Via application of the Marcus equation to the kinetic data, a very large value for the reorganization energy (λ = 62 kcal mol^–1) has been calculated for the C–S bond scission reaction in <b>1</b>^<b>+•</b>–<b>4</b>^<b>+•</b>