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Sarkar A.,University of Waterloo | Sarkar A.,Total EandP Canada Ltd. | Seth D.,University of Waterloo | Jiang M.,University of Waterloo | And 2 more authors.
Topics in Catalysis | Year: 2014

Structural characterization, the mechanism of catalytic activity generation and the nature of active sites of a NiSO4/γ-Al 2O3 catalyst for isobutene oligomerization were studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), diffuse reflectance infrared fourier transformed (DRIFTS) and X-ray photoelectron spectroscopy (XPS) techniques. The TPR measurements together with the XRD data indicated that calcination of the catalyst at 500 °C did not form either nickel oxide or nickel aluminate. The presence of only one type of surface nickel species formed by the incorporation of nickel ions into the surface vacant sites of γ-alumina lattice was indicated by XPS with Ar+ ions sputtering and TPR measurements. XPS analysis of the calcined catalyst suggested that the oxidation state of nickel ions in the calcined catalyst was (+2) and after calcination the nickel ions were coordinated to relatively more basic ligands. The surface acid centers of the catalyst were found to be only Lewis type. SO4 2- ions were found to be present as a chelating bidentate ligand and enhanced the acidity of metal Lewis acid centers. The results suggested that the combined effects of the presence of the bidentate SO4 2- ligand and dehydroxylation generate coordinatively unsaturated Ni 2 + that interact with isobutene during the oligomerization reaction. The formation of lower-valent nickel ions was demonstrated by in situ DRIFTS using CO as a probe molecule and by XPS measurements. Formation of a binuclear bridging carbonyl complex, 2 suggested that some lower-valent nickel species were formed via in situ reduction by isobutene. Analysis of Ni 2p photolines indicated the appearance of a new lower-valent nickel species during the course of isobutene oligomerization. Hence it is plausible that lower-valent nickel species might act as the active center for the oligomerization reaction, while the SO4 2- ions enhance the acidity of the Lewis acid sites on the surface and assist in the adsorption of reactant molecules on the surface. © 2014 Springer Science+Business Media New York. Source


Hu Y.-L.,CAS Shenyang Institute of Applied Ecology | Hu Y.-L.,University of Alberta | Yan E.-R.,East China Normal University | Choi W.-J.,Chonnam National University | And 5 more authors.
Plant and Soil | Year: 2013

Background and aims: Understanding changes in soil N cycling with stand development is critical for forest management as tree growth is affected by soil N availability. The aim of this study was to evaluate the changes in soil N availability and loss with stand development in trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.) in northeastern Alberta, Canada. Methods: Soil inorganic N availability (measured as N supply rate) and foliar N chemistry (N concentration and δ15N) in trembling aspen stands ranged from 52 to 70 years old (n = 7) and jack pine stands 43 to 78 years old (n = 8) were investigated in 2008 and 2009. The relationships among the ratios of NO3 --N to total inorganic N (NO3 --N/TIN), foliar N concentration, and foliar δ15N with stand age were also explored by regression analyses. Results: Total inorganic N supply rates did not systematically change with stand age across stand types, soil layers and measurement periods; whereas NO3 --N/TIN showed a decreasing tendency with stand age, suggesting that nitrification and associated N loss potential became smaller in older stands with greater limitation in soil N availability. Foliar δ15N decreased with stand age from -1.7 to -4.7‰ for aspen and from -4.1 to -7.1‰ for jack pine, and there were positive correlations between foliar δ15N and soil NO3 --N/TIN, suggesting that decreased soil N loss led to less 15N-depletion in the inorganic N available for tree uptake in older stands. However, foliar N concentration did not significantly change with stand age, suggesting that there were other N sources such as organic N in the forest floor, in addition to the inorganic N, available for plant uptake. Conclusions: Our results suggest that soil inorganic N availability became more limited as stand age increased. In addition, the ratio of NO3 --N/TIN and its relationship with foliar δ15N indicated decreased soil N loss potential and shifted N sources with stand age in boreal forests that are typically N-limited. Our study demonstrated that declining nitrification with increasing stand age might be one of the mechanisms mediating N-limitation in the studied boreal forests. © 2013 Springer Science+Business Media Dordrecht. Source


Li X.,University of Alberta | Li X.,CAS Nanjing Institute of Soil Science | Chang S.X.,University of Alberta | Salifu K.F.,Total EandP Canada Ltd.
Environmental Reviews | Year: 2014

Soil texture and its vertical spatial heterogeneity may greatly influence soil hydraulic properties and the distribution of water and solutes in the soil profile; therefore, they are of great importance for agricultural, environmental, and geo-engineering applications such as land reclamation and landfill construction. This paper reviews the following aspects on water and salt dynamics in the presence of a water table: (i) the effect of soil texture on the extent of upward movement of groundwater in homogenous soils and (ii) the impact of soil textural layering on water and salt dynamics. For a homogenous soil, the maximum height of capillary rise (hmax) or the evaporation characteristic length (ECL) is closely related to the soil texture. When the water table is deeper than hmax, water will evaporate at some depth below surface and salts will be retained below the evaporation front, causing the separation of water and salt. For layered soils, flow barriers (capillary and hydraulic barriers) can make the soil hold more water than a nonlayered one. A capillary barrier may work when a fine-textured layer overlies a coarse-textured layer during infiltration or a coarse-textured layer overlies a fine-textured layer during evaporation, and a hydraulic barrier may occur when a poorly permeable layer exists in the soil profile. The extra water held by flow barriers may improve water availability to plants and may at the same time increase salinization and other environmental risks. Under special conditions, such as in seasonally frozen soils with a shallow water table, there is an additional soil salinization incentive caused by freeze-thaw cycles. Above all, further research is needed to understand the complex effects of soil texture and layering on water and salt dynamics, especially in artificial soils such as reclaimed soils with contrasting properties. © 2013 Published by NRC Research Press. Source


Babak O.,Total EandP Canada Ltd. | Manchuk J.G.,University of Alberta | Deutsch C.V.,University of Alberta
Computers and Geosciences | Year: 2013

Facies models are used to better capture heterogeneity in mineral deposits and petroleum reservoirs. Facies are often considered as mutually exclusive and exhaustive at the scale of the geological model. These two assumptions are needed for sequential indicator simulation and most other facies modeling techniques; however, the assumption that an entire grid block consists of one facies type becomes unreasonable as the scale increases. Most geological models are built at a scale that is larger than the scale of variation of facies. Mixing of multiple facies types within a grid cell is common, especially in zones of transition between different facies. This paper develops a new technique to address the issue of non-exclusivity of facies within grid cells. The approach quantifies the uncertainty resulting from majority-vote upscaling of facies from core or well log scale to the grid cell scale and utilizes this uncertainty to build better models of continuous reservoir properties such as bitumen grade. Uncertainty is quantified using a measure of entropy that is capable of handling situations where there may be similarity between different facies types. A methodology to implement entropy in geo-modeling is introduced and demonstrated with several small examples. An example involving real data from the McMurray formation of Total's Joslyn lease is used to demonstrate the improvement in accuracy compared with traditional modeling workflows. © 2012 Elsevier Ltd. Source


Sarkar A.,University of Waterloo | Sarkar A.,Total EandP Canada Ltd. | Seth D.,University of Waterloo | Ng F.T.T.,University of Waterloo | Rempel G.L.,University of Waterloo
Industrial and Engineering Chemistry Research | Year: 2014

The kinetics of oligomerization of isobutene was studied on a NiSO4/γ-alumina catalyst in a stirred batch autoclave at temperatures of 50-90 °C and a pressure of 2170 kPa with different concentrations of isobutene. Experimental results revealed that the catalyst has high dimer selectivity and did not show any significant deactivation during the reaction. A generalized kinetic model based on a Langmuir-Hinshelwood (LH)-type reaction sequence was developed. The intraparticle diffusion effects inside the catalyst particle were correlated to the reaction rates and mass-transfer rate between the catalyst particle and liquid phase. The developed intrinsic kinetic model with estimated model parameters was found to describe the experimental data accurately. The magnitude of the activation energies was found to be in the range of 13-27 kJ mol-1, which suggests that the oligomerization reaction proceeds via surface rearrangement, as considered in the present LH-type kinetic model. © 2014 American Chemical Society. Source

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