Aimee MacLennan

Medium-energy microprobe station at the SXRMB of the CLS

Micro-XAFS and chemical imaging techniques have been widely applied for studies of heterogeneously distributed systems, mostly in hard X-ray (>5 keV) or in soft X-ray (<1.5 keV) energies. The microprobe endstation of the SXRMB (soft X-ray microcharacterization beamline) at the Canadian Light Source is optimized at the medium energy (1.7-5 keV), and it has been recently commissioned and is available for general users. The technical design and the performance (energy range, beam size and flux) of the SXRMB microprobe are presented. Examples in chemical imaging and micro-XAFS in the medium energy for important elements such as P, S and Ca for soil and biological samples are highlighted.

The catalytic activity and chemical structure of nano MoS2 synthesized in a controlled environment

A novel hydrothermal method for the preparation of nano MoS2 for hydrodesulfurization (HDS) with MoO3 as a precursor is presented. The redox reaction mechanism is, for the first time, revealed. It is shown to involve the oxidation of S2− to SO42− while hexavalent Mo is reduced to quadrivalent Mo to form MoS2. The HS− group is identified to play a key role in the reduction of MoO3. The interaction between Na2S and the HS− group and the yield of the resulting MoS2 are controlled via the pH of the synthesis solution. Various characterization methods, e.g. XRD, TEM, SEM, BET, TPR, XPS, XANES, EXAFS, etc., are employed for the characterization of the synthesized MoS2. The results show that high purity MoS2 is obtained. The ratio of precursors, MoO3 and Na2S, influences the crystal structure and catalytic activity. A slightly less amount of sulfur than the stoichiometric ratio of S/Mo produces defect sites, which promote catalyst activities in the hydrodesulfurization of real light cycle oil (LCO).

Effect of sulfate in mineral precursor on capacitance behavior of prepared activated carbon

Analog sulfur-containing precursors (ASCPs) were employed to prepare activated carbon (AC) for supercapacitor by potassium hydroxide (KOH) chemical activation. The influence of sulfate, K2SO4, FeSO4, and CaSO4 on pore structure of resultant AC and its capacitance performance was investigated extensively. The results indicate that FeSO4 and K2SO4 in ASCPs can be involved deeply in activation reaction. K2SO4 can play a synergistic activation role in increasing porosity and capacitance performance, while FeSO4 can react with and consume a certain amount of KOH, thus decreasing the performance of AC. Compared with K2SO4 and FeSO4, CaSO4 in ASCPs has low reactivity; namely, only a small part of CaSO4 was involved in activation reaction, while most of it was transformed into CaCO3 residued in AC during washing process. Due to coexistence of CaCO3 with AC, the porosity and capacitance performance of AC were decreased obviously. Furthermore, it is noteworthy that in comparison with K+ and Ca2+, Fe2+ in ASCPs is more beneficial for transformation of inorganic sulfate into organic thioether in AC.

Fischer–Tropsch Synthesis: XANES Spectra of Potassium in Promoted Precipitated Iron Catalysts as a Function of Time On-stream

XANES K-edge spectra of potassium promoter in precipitated Fe catalysts were acquired following activation by carburization in CO and as a function of time on-stream during the course of a Fischer–Tropsch synthesis run for a 100Fe:2K catalyst by withdrawing catalysts, sealed in wax product, for analysis. CO-activated and end-of-run spectra of the catalyst were also obtained for a 100Fe:5K catalyst. Peaks representing electronic transitions and multiple scattering were observed and resembled reference spectra for potassium carbonate or potassium formate. The shift in the multiple scattering peak to higher energy was consistent with sintering of potassium promoter during the course of the reaction test. The catalyst, however, retained its carbidic state, as demonstrated by XANES and EXAFS spectra at the iron K-edge, suggesting that sintering of potassium did not adversely affect the carburization rate, which is important for preventing iron carbides from oxidizing. The method serves a starting point for developing better understanding of the chemical state and changes in structure occurring with alkali promoter.Graphical Abstract

Vanadium Oxidation State Determination by X‐Ray Absorption Spectroscopy

Vanadium is found in slags produced during metal refinement and fossil fuel combustion/gasification. The oxidation state of vanadium in slag has technological and environmental implications. For example, it may affect slag flow and refractory wear inside reactors, as well as leachability and toxicity of industrial by-products. Determination of vanadium’s oxidation state in crystalline phases can be achieved via the widely adopted X-ray diffraction (XRD) technique. However, this technique does not provide information on vanadium in amorphous phases. The objective of this research is to determine the oxidation state of vanadium in petroleum coke gasification samples and laboratory samples using X-ray absorption spectroscopy (XAS) with Canadian Light Source’s soft X-ray micro-characterization beamline (SXRMB). Linear combination fitting of XAS spectra with reference samples allowed quantitative determination of vanadium speciation.

Effect of Phosphorus on the Activity and Stability of Supported Cobalt Catalysts for Fischer-Tropsch Synthesis

Phosphorus promotion on Fischer‐Tropsch (FT) synthesis was investigated for Co/Al2O3 and Co/SiO2 catalysts having the same Co/P ratio. When P is added to Co/Al2O3, CO conversion on a per g catalyst basis decreased, while methane selectivity increased. Catalyst stability was higher for the sample containing both P and Pt. The main cause for lower initial conversion is Co site blocking, while the lower extent of cobalt reduction for the P‐promoted Co/Al2O3 sample played a lesser role. When SiO2 is used to support cobalt particles, an initial induction period for the P‐promoted catalyst was observed, where CO conversion increased. Higher CO conversion at steady state, as well as improved catalyst stability during FT testing, suggest that P hindered sintering. Over the same period, a decline and leveling off of conversion were observed for the unpromoted catalyst. Completely different effects were observed depending on support type. P only acted as a poison for Co/Al2O3, whereas beneficial effects on steady state CO conversion and stability occurred with Co/SiO2. The different effects of P for Al2O3 and SiO2 supported Co catalysts can be explained by differences in Co‐support interactions. With alumina, Co clusters are already stabilized by strong interactions with the support. P has no benefit, as it mainly interacts with alumina instead of Co; pore blocking by P also occurred. In contrast, SiO2 has weak interactions with Co and less Co cluster stabilization. With P promotion, P anchors Co to the support, improving Co dispersion, stability and steady‐state conversion.