Palladium nanoparticle size effect in hydrodesulfurization of 4,6‐dimethyldibenzothiophene (4,6‐DMDBT)

Article
J. Shen, N. Semagina
ChemCatChem 8 (15), 2565-2571
Publication year: 2016

Optimal size: 8 nm Pd nanoparticles provide the deepest hydrodesulfurization as a result of balanced hydrogenation, sulfur extraction, and sulfur poisoning.

Pd nanoparticle size sensitivity of 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization was investigated by using 4, 8, 13, and 87 nm particles and was compared with the sulfur-free and sulfur-inhibited hydrogenation of 3,3-dimethylbiphenyl, which is a product of direct desulfurization of 4,6-DMDBT. The smallest 4 nm particles provided unprecedented (for Pd at 5 MPa and 300 °C) direct desulfurization selectivity of 20 % at 40 % conversion because of the reduced contribution of the hydrogenation path. The 4 nm particles were poisoned by the adsorbed sulfur to the greatest extent. The optimal size, providing the highest Pd mass-based yield of the desulfurized products, was found to be 8 nm. The catalyst with 87 nm particles was based on Pd nanocubes with the lowest edge/terrace surface atom ratio and large terraces and this showed the lowest sulfur extraction from both 4,6-DMDBT and sulfurous intermediates as a result of the low availability of edge atoms for a perpendicular sigma-mode adsorption through the lone pair of the sulfur atom. © 2016 Wiley-VCH.

Iridium addition enhances hydrodesulfurization selectivity in 4,6-dimethyldibenzothiophene conversion on palladium

Article
H. Ziaei-Azad, N. Semagina
Applied Catalysis B: Environmental 191, 138-146
Publication year: 2016

Highlights

  • Pd-Ir catalyst efficiently hydrodesulfurizes 4,6-dimethyldibenzothiophene.
  • Ir addition to Pd improves HDS selectivity to 93% vs. 38% for mono Pd.
  • Ir enhances direct desulfurization and C-S hydrogenolysis in hydrogenation.
  • Process pressure can be decreased from 5 to 3 MPa.

Abstract

38% to 93% selectivity enhancement toward sulfur-free products was observed upon iridium addition to a palladium-only catalyst in the hydrodesulfurization of a refractory sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) at the same 40% conversion from a 300 ppm, S-containing feed at 5 MPa and 300 °C. Pd promoted hydrogenation to sulfurous intermediates, while Ir catalyzed C-S hydrogenolysis and also improved Pd resistance to sintering. The selectivity in the direct desulfurization path for the Ir-containing catalysts increased up to 26% versus 5% for the Pd-only catalyst. The bimetallic catalyst allowed for a decrease in S from 300 ppm to 11 ppm. It can be used at reduced pressure (3 MPa) with only a 15% decrease in hydrodesulfurization conversion as compared to the operation at 5 MPa. © 2016 Elsevier, reprinted with permission.

Enhanced CH4 yield by photocatalytic CO2 reduction using TiO2 nanotube arrays grafted with Au, Ru, and ZnPd

Article
P. Kar, S. Farsinezhad, N. Mahdi, Y. Zhang, U. Obuekwe, H. Sharma, J. Shen, N. Semagina, K. Shankar
Nano Research 9 (11), 3478-3493
Publication year: 2016

Metal nanoparticle (NP) co-catalysts on metal oxide semiconductor supports are attracting attention as photocatalysts for a variety of chemical reactions. Related efforts seek to make and use Pt-free catalysts. In this regard, we report here enhanced CH4 formation rates of 25 and 60 μmol·g–1·h–1 by photocatalytic CO2 reduction using hitherto unused ZnPd NPs as well as Au and Ru NPs. The NPs are formed by colloidal synthesis and grafted onto short n-type anatase TiO2 nanotube arrays (TNAs), grown anodically on transparent glass substrates. The interfacial electric fields in the NP-grafted TiO2 nanotubes were probed by ultraviolet photoelectron spectroscopy (UPS). Au NP-grafted TiO2 nanotubes (Au-TNAs) showed no band bending, but a depletion region was detected in Ru NP-grafted TNAs (Ru-TNAs) and an accumulation layer was observed in ZnPd NP-grafted TNAs (ZnPd-TNAs). Temperature programmed desorption (TPD) experiments showed significantly greater CO2 adsorption on NP-grafted TNAs. TNAs with grafted NPs exhibit broader and more intense UV–visible absorption bands than bare TNAs. We found that CO2 photoreduction by nanoparticle-grafted TNAs was driven not only by ultraviolet photons with energies greater than the TiO2 band gap, but also by blue photons close to and below the anatase band edge. The enhanced rate of CO2 reduction is attributed to superior use of blue photons in the solar spectrum, excellent reactant adsorption, efficient charge transfer to adsorbates, and low recombination losses. © 2016, Tsinghua University Press and Springer, reprinted with permission.

Catalysts and process for hydrodesulfurization

Patent
N. Semagina, H. Ziaei-Azad
Patent CA2889960
Publication year: 2016

The present invention is directed to a catalyst for hydrodesulfurization of thiohydrocarbons, said catalyst comprising highly dispersed nanoparticles of a transition metal selected from the group consisting of: iridium, palladium and iridium/palladium and methods of manufacture thereof.

Structural evolution of bimetallic Pd-Ru catalysts in oxidative and reductive applications

Article
J. Shen, R.W.J. Scott, R.E. Hayes, N. Semagina
Applied Catalysis A: General 502, 350-360
Publication year: 2015

Highlights

  • Pd-Ru alloy and Pd(core)-Ru(shell) samples are prepared with the same composition.
  • At mild catalytic reaction conditions, the core–shell structure is preserved.
  • In reductive catalysis at 350 °C, some Pd migration to the surface occurs.
  • In oxidative catalysis up to 500 °C, both samples show identical behavior.
  • In the latter case, the final structure of both catalysts has Pd rich shells.

 Abstract

Two types of bimetallic Pd-Ru catalysts with a 2:1 Ru:Pd molar ratio were prepared using a poly-(vinylpyrrolidone) stabilizer: one alloy structure with mixed-surface atoms and one core–shell structure with a Pd core and Ru shell, which were confirmed by a surface-probe reaction at mild conditions. In indan hydrogenolysis at 350 °C, inversion of the core–shell structure began with Pd atoms appearing on the surface of the particles. Both catalysts displayed distinctively different catalytic behavior and indicated the importance of structure control for this particular application within a studied time frame. For methane combustion over the 200–550 °C temperature range, both structures demonstrated identical activity, which was due to their structural evolution to one nanoparticle type with Pd-enriched shells, as evidenced by extended X-ray absorption fine structure. © 2015 Elsevier, reprinted with permission.

How to design silent control experiments for ultrasound-assisted oil sands extraction and upgrading: A computational study

Article
N. Semagina, C.F. Lange
Journal of Petroleum Science and Engineering 126, 83-86
Publication year: 2015

Highlights

  • Acoustic oil sands extraction and upgrading was analyzed in terms of power input.
  • High temperature rise was computed if 100% acoustic energy were dissipated as heat.
  • The control silent experiments should be performed at the same power input.

Abstract

The major concern in estimating sonochemical yield and efficiency in ultrasound-assisted processes is in defining a “silent” control experiment, without cavitation effects. To estimate the potential benefit of the ultrasonic treatment as compared to conventional heating, we propose that the effects should be compared at the same power input, when the energy in a silent experiment is dissipated as heat. Our calculations of possible temperature increase under the silent conditions for oil sands extraction and upgrading showed necessity of such approach. © 2015 Elsevier, reprinted with permission.

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.