Impacts of nickel loading on properties,catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO₂ over Ni/Al₂O₃ with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO₂ dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO₂ showed that CO₂ could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO¹ species and ¹CH₃ species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.     

Mechanistic study of Ce–La–Fe/γ-Al2O3 catalyst for selective catalytic reduction of NO with NH3

A number of Ce–La–Fe/γ-Al₂O₃ catalysts were prepared by impregnation and microwave hydrothermal heating based on the ratio of Ce, La, and Fe in natural bastnäsite to examine the synergistic relationship between Ce, La, and Fe in natural bastnäsite and its effects on ammonia selective catalytic reduction (NH₃-SCR). The results demonstrated that an increase in Fe species is beneficial to the denitration performance of catalysts with a Ce:La:Fe mole ratio of 1:0.6:0.12, thus providing high NO conversion (>95%) at 350 °C. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy results confirmed the formation of a solid solution between Ce, La, and Fe in the catalysts. The BET isotherms and NH₃-TPD demonstrated that the addition of Fe increased the surface area and strengthened the surface acidity of Lewis acid sites. XPS and in situ DRIFTS indicated that electron transfer occurred between Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox cycles in the catalyst, thereby improving the adsorption and activation ability of NO and NH₃. NO species were adsorbed on the catalysts in the form of monodentate nitrate, and then monodentate nitrate was oxidized to bidentate nitrate. The SCR reaction route was the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms.     

In situ diagnosis of micrometallic proton exchange membrane fuel cells using microsensors

This work utilizes the microsensors that are fabricated on metallic bipolar plates to measure temperature and humidity in an operating micro-proton exchange membrane fuel cell (PEMFC). Bipolar plates were constructed of stainless steel (SS-304), and the flow channel was formed on a stainless steel substrate by wet etching. The micro-temperature and humidity sensors were fabricated using micro-electro-mechanical-systems (MEMS) technology. The sensors were located on the flow channel rib.     

In situ X-ray diffraction of prototype sodium metal halide cells: Time and space electrochemical profiling

The feasibility of using energy dispersive X-ray diffraction to characterize full size battery cells is demonstrated by unprecedented in situ measurements of the electrochemical processes taking place inside high temperature sodium metal halide (Na/MCl₂, M = Ni and/or Fe) cells during charge/discharge cycling. Diffraction data provide phase information either via line scans across the 5 cm wide cells or via fixed location scans as a function of time. The data confirm the propagation of a well-defined chemical reaction front, as a function of charge/discharge time, beginning at the ceramic separator and proceeding inward. Measurement of the temporal evolution of the phase abundances yields mechanistic understanding and reaction rates as a function of charge/discharge state. In the case where M includes Fe, the data also clearly show the appearance of an intermediate phase, Na₆FeCl₈, during charging, thereby underscoring the power of this technique to reveal subtle mechanistic information. A number of additional detailed electrochemical kinetic effects are also discussed. This study shows that in situ high energy X-ray diffraction characterization of advanced battery cells in space and time is eminently feasible on a routine basis, and has great potential to advance the understanding of “buried” chemical processes.     

In-situ synthesis of Ag-Pi oxygen-evolving catalyst in phosphate environment for water splitting

An efficient Ag-P_i oxygen-evolving catalyst was fabricated in situ in a phosphate electrolyte solution (pH 12.4). The catalyst approaches an amorphous structure, unlike the reported Ag-based oxygen-evolving catalysts. The catalytic activity for water oxidation of the Ag-P_i catalyst is 11.1 μmol h^?1 cm^?2 and it has a modest oxygen-evolution overpotential of 457.0 mV at 1 mA cm^?2 in 0.1 M K₃PO₄ electrolyte. The effects of different electrolytes on the formation of the Ag-P_i catalyst were investigated. The active component of the Ag-P_i oxygen-evolving catalyst as a water-splitting catalyst is the AgO phase as determined by X-ray diffractometry and X-ray photoelectron spectroscopy analysis. A Ag-P_i mechanism that includes the Ag(I) and Ag(III) cycles is proposed to explain the electrocatalytic oxygen evolution.     

Catalytic effect of titanium nitride nanopowder on hydrogen desorption properties of NaAlH4 and its stability in NaAlH4

Single crystalline titanium nitride (TiN) nanopowder is synthesized by a mechano-chemical reaction between titanium chloride (TiCl₃) and lithium nitride (Li₃N) by means of high-energy ball milling. The TiN nanopowder has an average particle size of 6 nm and is introduced into sodium alanate (NaAlH₄) as a catalyst. During hydrogen sorption cycles, TiN-catalyzed NaAlH₄ exhibits a greater hydrogen desorption rate and higher hydrogen capacity than TiCl₃-catalyzed NaAlH₄. Contradicting thermodynamic predictions, in situ X-ray diffraction results reveal that TiN nanopowder remains stable and produces no by-products (e.g., Ti-Al compounds) in the reaction with NaAlH₄ during hydrogen desorption. In situ Raman spectroscopy also confirms the stability of TiN nanopowder in NaAlH₄. This implies that the sustained hydrogen sorption kinetics and hydrogen capacity of TiN-catalyzed NaAlH₄ originate from the structural and chemical stability of TiN nanopowder in NaAlH₄ for the given conditions of the hydrogen cycle test.     

The effect of reduction of pretreated NiO–ZnO catalysts on the water–gas shift reaction for hydrogen production as studied by in situ DRIFTS/MS

The water–gas shift (WGS) reaction on co-precipitated NiO–ZnO catalysts at different reduction temperatures has been studied by a temperature-programmed reaction using in situ diffuse reflectance infrared Fourier Transform Spectroscopy, coupled with mass spectroscopic (in situ DRIFTS/MS) techniques. The results reveal that a catalyst reduced at 493 K (labeled H220) showed higher activity than one reduced at 673 K (labeled H400) due to the ability of NiO on the H220 catalyst to promote CO conversion of the WGS reaction. In situ DRIFTS/MS studies show that there are three adsorbed species over the H220 catalyst at room temperature: adsorbed CO bands, molecularly adsorbed H₂O and carboxyl species. Increasing the temperature to 423 K led to the emergence of CO₂ and H₂ and the disappearance of carboxyl species. However, the low catalytic activity of the H400 catalyst could be attributed to the conversion of the NiO sites to reduced Ni metal sites, which (i) adsorbed CO as the strong linearly bonded CO on the catalyst surface, slowing down the CO reaction, and (ii) showed a lower H₂O uptake.     

In situ XRD for pseudo Laves phases hydrides highlighting the remained cubic structure

The hydrogenation behaviour of the Gd_0.5Y_0.5Ni_3.75Al_0.25Mg compound was studied by in situ X-ray diffraction under hydrogen pressure and at room temperature. The presence of gadolinium induce an exchange between the 4a (occupied by RE) and 4c sites (occupied by Mg). Nevertheless, only the Gd atoms are mixed by Mg atoms and no occurrence of Y/Mg mixing can be observed. The exchange is then directly correlated with the 4f electrons. Moreover, in the compounds without Gd (i.e. YNi_3.75Al_0.25Mg) no exchange was observed. The structure of the metal hydrides was carefully investigated by refining the in situ XRD patterns obtained under various H₂ pressures. It was concluded that the structure remains cubic during the sorption process with an increase of the cell volume close to 13%, in agreement with the maximum sorption capacity (i.e. 3H/formula unit). No variation of the exchange rate between the hydride and the initial intermetallic can be highlighted. The changes of both the crystallite size and lattice strains during the sorption process (i.e. along the PC isotherms) indicated that a decrease of the crystallinity is observed but no HIA process occurred.     

Approaches to extracting potentially recoverable hydrocarbons

The current status of nuclear-explosive fracturing to improve gas production from tight formations and in situ combustion to enhance oil recovery from existing reservoirs are assessed. The current status of projects Gasbuggy, Rulison and Rio Blanco are presented, and it is pointed out that production predictions were considerably overestimated. Several hypotheses to account for this are presented, but the most important seems to be overstimated formation permeability. the limitations of the current technology are discussed, and the greatest obstacle to progress is recognised as public nonacceptability of the technique. The basic processes of in situ combusion for enhanced oil recovery are presented together with a comparison of the recovery efficiency with those of other processes. It is shown that the method offers the highest percentage of oil recovery in heavy oil prospects of any thermal recovery methods proposed so far. However, the method is expensive and highly complex, but it is likely that it is the most widely applicable and that important improvements will be made in the next decade.     

In situ X-ray diffraction under H2 of the pseudo-AB2 compounds: YNi3.5Al0.5Mg

The hydrogenation and dehydrogenation behaviours of the YNi_3.5Al_0.5Mg compound were studied by in situ X-ray diffraction under hydrogen pressure and at room temperature. The changes of (i) the lattice parameters, (ii) the crystallite size and (iii) the lattice strain during the sorption process (i.e. along the PC isotherms) were studied. These results indicate that the crystallite size decreases by a factor of 2. The micro deformations increase at first and then tend to almost zero at the end of the sorption cycle. This behaviour is explained in terms of co-existence of the metal (i.e. α$\alpha$ phase) and metal hydride (i.e. β$\beta$ phase) phases. The change in crystallinity is consistent with the hydrogen induced amorphisation process existing in a lot of AB₂ compounds. No anisotropic effects can be highlighted on this pseudo-AB₂ compounds in contrary with what could be observed in AB₅ compounds.     

Hydrogen-rich gas production from pyrolysis of wet sludge in situ steam agent

A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 °C exhibited maximum H₂ yield (7.76 mol kg^?1 dry basis wet sludge) and dry gas yield (0.61 Nm³ kg^?1) and H₂ content of 42.13 vol%. When the moisture exceeded 43.38%, H₂ yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H₂ yield and H₂ content were increased from 1.83 mol kg^?1 dry basis wet sludge and 16.67 vol% to 9.15 mol kg^?1 dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 °C to 850 °C. LHV of fuel gas varies from 15.49 MJ Nm^?3 to 11.65 MJ Nm^?3 because of decrease in CH₄ and C₂H₄ content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method.