100° Temperature reduction of wet methane combustion: highly active Pd–Ni/Al2O3 catalyst versus Pd/NiAl2O4

Article
J. Shen, R.E. Hayes, X. Wu, N. Semagina
ACS Catalysis 5 (5), 2916-2920
Publication year: 2015

The crucial role of Ni mode addition to Pd catalysts for low-temperature wet methane combustion is addressed, resulting in excellent performance of ultralow-Ni-containing catalysts versus inactive nickel–alumina spinel. Traditional impregnation–calcination and colloidal techniques of bimetallic catalyst preparation yield monometallic Pd particles on a binary NiAl2O4 support and Pd and Ni nanoparticles on the parent Al2O3 support, respectively. The catalyst is potentially valuable for natural gas catalytic combustion technologies because it decreases the required temperature for complete methane combustion in 5% water presence in the feed by 100 degrees versus monometallic Pd. © 2015 American Chemical Society, reprinted with permission.

Nickel boosts ring‐opening activity of iridium

Article
H. Ziaei‐Azad, N. Semagina
ChemCatChem 6 (3), 885-894
Publication year: 2014

Save the rare: To avoid inefficient use of rare and expensive catalytic metals, iridium atoms are placed only in the outermost layer of the nanoparticles, with inexpensive metal (nickel) inside, which boosts the catalytic performance:

A variety of bimetallic Ni–Ir catalysts were synthesised by preforming nanoparticles in the presence of polyvinylpyrrolidone, followed by deposition on γ-alumina and high-temperature polymer removal. The Ni–Ir (1:1 molar ratio) nanoparticles prepared by the hydrogen-sacrificial technique (Ir reduction on the preformed Ni nanoparticles with surface Ni hydride) allowed increasing indane ring opening activity per total amount of Ir as compared to monometallic Ir. The simultaneous reduction of Ni and Ir precursors was not as efficient. The catalysts were characterised with UV/Vis spectroscopy, TEM, temperature-programmed reduction, CO2temperature-programmed desorption, CO diffuse reflectance Fourier transform spectroscopy, X-ray photoelectron spectroscopy and CHN analysis. The study only explored the catalyst’s metal function and allows saving rare and expensive iridium without loss of its outstanding performance as a ring-opening catalyst. © 2014 Wiley-VCH.

Negative impact of high stirring speed in laboratory-scale three-phase hydrogenations

Article
I. Ayranci, S. Kresta, J. Shen, N. Semagina
Industrial & Engineering Chemistry Research 53 (46), 18091-18094
Publication year: 2014

An increase in stirring speed is generally considered to be an a priori means of reducing external mass-transfer limitations in fast three-phase hydrogenations that are performed in a stirred tank. We provide experimental evidence for a 300-mL stirred reactor that, above a certain impeller speed, the efficiency of gas–liquid mass-transfer decreases, resulting in the decreased reaction rate. The phenomenon is attributed to the high degree of gas recirculation with large cavities behind the blades. The recirculation may decrease hydrogen concentration in the remainder of the tank, thus decreasing the concentration gradient that controls mass transfer. The model reaction in this work was 2-methyl-3-butyn-2-ol semihydrogenation with Lindlar catalyst Pd–Pb/CaCO3. The test impellers were a Rushton turbine, a down-pumping pitched blade turbine, and up-pumping A340 impellers. The kinetic experiments were combined with the measurement of volumetric gas–liquid mass-transfer coefficient, flow pattern analysis and impeller power demand calculations. Although the study does not include kinetic analysis, it provides guidance to the three-phase reaction system analysis that the highest stirring speed may enhance mass-transfer limitations and should not be used without caution. © 2014 American Chemical Society, reprinted with permission.

Is it always necessary to remove a metal nanoparticle stabilizer before catalysis?

Article
J. Shen, H. Ziaei-Azad, N. Semagina
Journal of Molecular Catalysis A: Chemical 391, 36-40
Publication year: 2014

Highlights

  • Ru and Ir nanoparticles were stabilized by PVP and deposited on alumina.
  • The effect of calcination–reduction treatments was studied.
  • For efficient ring opening catalysis, complete stabilizer removal is not necessary.
  • For CO chemisorption, complete stabilizer removal is mandatory.

 

Abstract

The answer is no. It depends on the catalyzed reaction and the active metal. For Ru and Ir nanoparticles stabilized by polyvinylpyrrolidone (PVP), their activities in an indan ring opening are not affected by the residual polymer, while CO chemisorption requires complete polymer removal. The in situ cleaning effect of the reaction atmosphere was found negligible. The findings are supported by TEM, XPS, CHN analysis, indan- and CO-TPD, CO chemisorption analyses and catalytic measurement. The necessity for complete polymer removal must be evaluated on a case-by-case basis; in some cases mild catalyst pretreatment is enough. © 2014 Elsevier, reprinted with permission.

Bimetallic catalysts: Requirements for stabilizing PVP removal depend on the surface composition

Article
H. Ziaei-Azad, N. Semagina
Applied Catalysis A: General 482, 327-335
Publication year: 2014

Highlights

  • Effect of PVP removal on catalysis by bimetallic nanoparticles was studied.
  • Pd–Ir catalysts stabilized by PVP were tested after calcination treatments.
  • Ring opening activity of catalysts with Ir-rich surface does not require clean surface.
  • Pd-rich catalysts must be cleaned before the catalysis.

Abstract

Alloy and core–shell bimetallic Pd–Ir nanoparticles stabilized by polyvinylpyrrolidone (PVP) and deposited on alumina were subjected to PVP removal via thermal treatments. Less than 25% of the PVP was removed at 200 °C calcination/375 °C reduction, while the 400 °C calcination eliminated over 95% of PVP. The treated samples were tested in the gas-phase ring opening of indane at 350 °C. The cleaning was paramount for the bimetallic catalysts with Pd-rich surfaces that only exhibited activity after 400 °C calcination, while the catalysts with Ir-rich surfaces were similarly active irrespective of the presence or absence of the PVP residuals. For the CO chemisorption, complete cleaning was required for all catalysts. The study is supported by CO-DRIFTS, CO-TPD, indane-TPD, carbon analysis, TEM, CO chemisorption and catalytic measurements, and shows that the necessity to remove PVP depends on the nature of metals in bimetallic catalysts and their surface arrangements. © 2014 Elsevier, reprinted with permission.

Suppression of addition reactions during thermal cracking using hydrogen and sulfided iron catalyst

Article
F.K. Habib, C. Diner, J.M. Stryker, N. Semagina, M.R. Gray
Energy & Fuels 27 (11), 6637-6645
Publication year: 2013

Due to the complexity of the vacuum residue fraction of petroleum and bitumen, a model compound was used to probe cracking and addition reactions in the liquid phase. Hydrogenation reactions were conducted in a batch microreactor at 430 °C, 13.9 MPa H2 for 30 min using a solution of 1,3,6,8-tetrahexylpyrene (THP) in tetralin. Sulfided iron was prepared on α-alumina, γ-alumina, and glass beads as support materials. The hypothesis of this study was that addition reactions can be suppressed under hydrogenation conditions by using iron sulfide as a low-activity catalyst in the presence of hydrogen gas and a hydrogen donor solvent, by saturating olefin intermediates. The products were analyzed by high performance liquid chromatography, gas chromatography, matrix-assisted laser desorption ionization mass spectrometry, and proton nuclear magnetic resonance spectroscopy to investigate conversion and product distribution for different catalysts and without added catalyst. The results show that sulfided iron can give significant suppression of addition reactions, decreasing from 63 mol % for the noncatalytic reaction to 13 mol % under catalytic conditions, and shifting the selectivity toward cracking, without competitive hydrogenation of the aromatics. The catalysts were characterized by measuring bulk and surface composition, and by scanning electron microscopy before and after the reaction. The data show that catalyst does not have an impact on conversion; therefore, the data do not support the claim that free radicals are efficiently hydrogenated. The results confirm the presence of iron sulfide on the catalyst surface and a change in its crystalline structure from pyrite to pyrrhotite during reaction. This study shows the value of using a low-cost iron catalyst, as compared to the commercial nickel-based catalysts, as an additive to reduce the amount of coke formation in thermal cracking processes conducted in the presence of hydrogen. © American Chemical Society, reprinted with permission.

Size-and structure-controlled mono-and bimetallic Ir–Pd nanoparticles in selective ring opening of indan

Article
H. Ziaei-Azad, C.X. Yin, J. Shen, Y. Hu, D. Karpuzov, N. Semagina
Journal of Catalysis 300, 113-124
Publication year: 2013

Highlights

  •  Size- and structure-controlled Pd/Ir mono- and bimetallic particles were synthesised.
  •  Two contiguous surface Ir atoms form an active site in indan ring opening (RO).
  •  Pd serves as an inert surface diluting or Ir dispersing agent.
  •  Pd(core)Ir(shell) gives 19% higher selective RO yield than industrial PtIr catalyst.

Abstract

Nearly monodispersed 1.6 nm Ir, 2.3 nm Pd nanoparticles, 2.7 nm Pd(core)–Ir(shell) and 2.2 nm Pd–Ir alloys with mixed surface atoms were synthesised in the presence of polyvinylpyrrolidone (PVP) and studied in the atmospheric ring opening of indan. The nanoparticles and supported catalysts were characterised by UV–vis spectroscopy, TGA, TEM, EDX, TPR, XPS, ISS and XANES. The nanoparticle size and structure control allowed insights into the bimetallic catalyst functioning. As soon as two contiguous surface Ir atoms exist on the nanoparticle surface, they display the same catalytic properties, most likely through the dicarbene ring-opening mechanism. Palladium serves only as a dispersing agent in Pd(core)–Ir(shell) structures providing 100% Ir dispersion, or as an inert surface diluting metal in Pd–Ir formulations with mixed nanoparticle surface. The Pd–Ir core–shell structure allows maximum selective ring-opening yield, which is 19% higher than that for the industrial Pt–Ir catalyst. © 2013 Elsevier, reprinted with permission.

PVP-stabilized mono-and bimetallic Ru nanoparticles for selective ring opening

Article
J. Shen, X. Yin, D. Karpuzov, N. Semagina
Catalysis Science & Technology 3 (1), 208-221
Publication year: 2013

Selective ring opening of naphthenic molecules in oil upgrading should result in no loss in molecular weight. Benzocyclopentane (indan) ring opening was studied under hydrogen atmospheric pressure at 609 K over poly-(vinylpyrrolidone)-stabilized Ru, Ir and Pd monometallic and Ru–Ir and Ru–Pd bimetallic nanocatalysts prepared by simultaneous reductions. The particle size (mostly within 2 nm) and their monodispersity were confirmed by transmission electron microscopy, while X-ray photoelectron spectroscopy indicated the bimetallics’ alloy structure. Pd catalysts displayed the lowest activity in the ring opening; Ru showed the highest formation of undesired o-xylene and lights. Monometallic Ir displayed the highest activity and selectivity toward 2-ethyltolueneand n-propylbenzene. In bimetallic structures, higher Ir content led to improved catalytic performance. Next to the monometallic Ir catalyst, the newly developed Ru1Ir4/γ-Al2O3 catalyst (with 1 : 4 molar ratio of Ru to Ir) displayed superior single cleavage selectivity as well as lower cracking activity compared to industrial Pt–Ir catalysts at a comparable indan conversion. The study can pave the way in the development of Pt-free Ru-containing catalystswith narrow size distributions for selective ring opening, especially taking into consideration a possibility of their higher S-resistance as compared to the Pt catalysts. © 2013 The Royal Society of Chemistry, reproduced with permission.

Platinum-free monometallic and bimetallic nanoparticles as ring-opening catalysts

Patent
N. Semagina, X. Yin, J. Shen, K. Loganathan
Patent CA2803331, US9040449, US20130248414
Publication year: 2013

Nanoparticle catalyst compositions and methods for preparation of same are described. The nanoparticle catalysts are platinum-free and are useful in effecting selective ring-opening reactions, for example in upgrading heavy oil. The catalyst may be of monometallic composition, or may comprise an alloyed or core-shell bimetallic composition. The nanoparticles are of controlled size and shape.

Iridium-and platinum-free ring opening of indan

Article
J. Shen, N. Semagina
ACS Catalysis 4 (1), 268-279
Publication year: 2013

A 3- and 2-fold increase in selectivities toward 2-ethyltoluene and n-propylbenzene, respectively, in indan ring opening (RO) was achieved by introducing palladium to the ruthenium catalyst. The product selectivities for the Ru–Pd system with the 4:1 molar ratio were the same as those for monometallic iridium, known for its outstanding single cleavage selectivity; the lights formation was suppressed as compared with the monometallic platinum catalyst. A further increase in the Pd amount did not result in the selectivity improvement and brought down the activity to the low level of Pd. The bimetallic catalysts were synthesized in the presence of poly-(vinylpyrrolidone). The bimetallic systems revealed sintering resistance up to 400 °C, as compared with their monoforms. The indan RO activity was maximized after precalcination at 200 °C. The suggested nanoparticles’ bimetallicity was consistent with the results of CO-TPD, CO–DRIFTS, thermal stability tests, and a chemical probe reaction (olefin hydrogenation, in which only Pd is active). The Pd–Ru system is envisioned as a viable alternative to monometallic Ir for RO.  © 2014 American Chemical Society, reprinted with permission.

Electrochemical behavior of tungsten carbide-based materials as candidate anodes for solid oxide fuel cells

Article
A. Torabi, T.H. Etsell, N. Semagina, P. Sarkar
Electrochimica Acta 67, 172-180
Publication year: 2012

Tungsten carbide-based electrodes under mixed hydrogen–methane and methane fuels have been investigated as potential anode materials for solid oxide fuel cell (SOFC) application. Firstly, it was shown that hydrogen is not a suitable fuel for the carbide-based materials. A conventional WC–YSZ composite and a carbide infiltrated porous YSZ support were then studied. Ac impedance spectroscopy revealed that the ohmic resistance and the charge-transfer polarization of these cells were reasonably low. The chemical reaction polarization, however, was relatively large, particularly under methane fuel. The carbide-based electrodes were then modified by incorporation of ceria and/or ruthenium. Not only did the co-existence of CeO2 and Ru synergically enhance the cell performance, more importantly it also greatly improved the stability of the polarized cell. Although bulk phase analysis confirmed the presence of a minor amount of tungsten oxide, surface analysis showed that the oxide phase remained superficial. It was then proposed that surface oxidation of the carbide phase was essentially a part of the fuel oxidation process and, as long as the rate of carbide oxidation and that of oxide recarburization remained comparable, the cell performance was stable.  © 2012 Elsevier, reprinted with permission.

Structured catalysts via multiple stage thermal oxidation synthesis of FeCrAl alloy sintered microfibers

Article
J.E. Samad, J.A. Nychka, N.V. Semagina
Chemical Engineering Journal 168 (1), 470-476
Publication year: 2011

A structured catalyst support was developed based on FeCrAl alloy sintered microfibers (SMF) via multiple stage thermal oxidation in air for 1 h at 930 °C, 1 h at 960 °C and 2 h at 990 °C. The procedure resulted in the formation of a forest of predominantly α-alumina whiskers (200 nm in height and 100 nm apart). Palladium deposition and reduction yielded 0.5 wt.% Pd/SMF with 20 nm nanoparticle size. The catalyst was tested in three-phase hydrogenation of 2-methyl-3-buten-2-ol, and due to its pore structure allowed eliminating internal mass transfer limitations. The developed support can be beneficial to catalytic reactions suffering from mass transfer limitations and catalyst deactivation via pore mouth blocking. As compared to other methods of structured catalyst preparation, the thermal oxidation procedure is simple, fast and environmentally benign, and eliminates problems associated with poor adhesion of traditional washcoated layers of powdered catalysts or supports.  © 2011 Elsevier, reprinted with permission.

Size- and shape- controlled Pd nanoparticles in a fluorometric Tsuji-Trost reaction

Article
Y. Yang, L.D. Unsworth, N. Semagina
Journal of Catalysis 281 (1), 137-146
Publication year: 2011

Pd nanoparticles catalyze Tsuji–Trost reaction for Pd fluorometric detection in the presence of PPhvia atomic dissolution:

Highlights

  • Pd nanoparticles catalyze Tsuji–Trost reaction used for Pd fluorometric detection.
  • Nanoparticle activity is correlated with the number of defect surface atoms.
  • The reaction occurs via atomic dissolution and Ostwald ripening.
  • The highest rate is concomitant with the formation of largest nanoparticles.
  • Optimum PPh3 concentration exists for the fastest reaction.

Abstract

Palladium nanospheres of 2.4 and 3.8 nm diameter and nanocubes of 18 nm rib length were used to catalyze a fluorometric Tsuji–Trost reaction for the transformation of a phenyl allyl ether to a fluorescent phenol in the presence of triphenylphosphine, which was pivotal to the catalytic activity. Turnover frequencies calculated per defect atoms were found similar for all nanoparticles, indicating that these atoms are the active sites. However, kinetic studies combined with Pd leaching and transmission electron microscopy analyses in the presence of various reaction components showed Pd leaching via oxidative addition of a reactant, followed by nanoparticle growth depending on the PPh3 concentration. The formation of largest particles was found for the fastest reaction with PPh3/Pd molar ratio of 4, in the range from 0 to 9. This study shows the validity of the atomic dissolution mechanism in the reaction of interest. © 2011 Elsevier, reproduced with permission.

Kinetics of catalytic steam gasification of bitumen coke

Article
A. Karimi, N. Semagina, M.R. Gray
Fuel 90 (3), 1285-1291
Publication year: 2011

The catalytic steam gasification of coke from Athabasca bitumen was investigated by thermogravimetric analysis using K2CO3 and Na2CO3 as catalysts, both of which reduced the activation energy of the reaction considerably to 1.2 × 105 J mol−1 and 1.3 × 105 J mol−1, respectively, down from 2.1 × 105 J mol−1 for the uncatalyzed reaction. The reaction rates varied with the partial pressure of steam between 60 kPa and 85 kPa consistent with a Langmuir–Hinshelwood model, but a first order equation was also sufficient given the low partial pressures. The initial rate of gasification of the coke particles correlated linearly with the estimated external surface area of the particles, as expected from a surface reaction involving a non-porous solid. The initial reaction rate increased with increasing the catalyst loading up to 2.4 (mol potassium)/kg. A portion of the catalyst penetrated into the coke, as confirmed by secondary ion mass spectroscopy analysis, where it could not promote the reaction with steam. This result was consistent with a small increase observed in the reaction rate at low catalyst loading. The shrinking core model was successful in predicting the rates at higher conversions from the initial rate data, despite increases in BET surface area with conversion. © 2011 Elsevier, reprinted with permission.

Nanoparticle shape effect study as an efficient tool to reveal the structure sensitivity of olefinic alcohol hydrogenation

Article
R. Ma, N. Semagina
The Journal of Physical Chemistry C 114 (36), 15417-15423
Publication year: 2010

Monodisperse Pd nanocubes of 20 nm rib length and Pd nanospheres of 3.0 nm diameter were synthesized in the presence of cetyltrimethylammonium bromide and used to investigate the structure sensitivity of three-phase 2-methyl-3-buten-2-ol hydrogenation. Turnover frequencies per all surface atoms were found as 2.58 s−1 for the cubes and 3.86 s−1 for the spheres at 313 K, indicating that (100) atoms of the cubes comprising ∼98% of all surface atoms have lower activity than other surface atoms of the spheres, composed of atoms on (111), (100) terraces, edges, and vertices. Apparent activation energies of 23 kJ/mol for the cubes and 17 kJ/mol for the spheres in the verified kinetic regime confirmed the reaction structure sensitivity. Assuming that only (100) and (111) atoms are active on the sphere surface, a hypothetical most active Pd nanostructure was predicted as a tetrahedron allowing twice higher activity per Pd loading as compared to a spherical particle. © 2010 American Chemical Society, reprinted with permission.