Presence Of Steam Research Articles

Bio-oil chemical looping reforming coupled with water splitting for hydrogen and syngas coproduction: Effect of supports on the performance of Ni-Fe bimetallic oxygen carriers

In this study, chemical looping reforming coupled with water splitting (CLRWS) process for coproduction of syngas and hydrogen using bio-oil model compound as fuel was investigated. The process simulation results indicated that the mass ratio of fuel to Fe2O3 (F/O) of 0.3 at 900 °C was suitable for syngas and hydrogen coproduction. Under these conditions, the CLRWS experiments were conducted in the fixed bed reactor using Ni-Fe bimetallic oxygen carriers (OCs). The Ni-Fe bimetallic oxygen carrier contained 5 wt% of NiO, 60 wt% of Fe2O3 and 35 wt% of support. Six metal oxides, Al2O3, CeO2, La2O3, MgO, TiO2 and ZrO2, were used as supports, and corresponding OCs were termed as NFA, NFC, NFL, NFM, NFT and NFZ, respectively. The interaction between different components had significant influence on coproduction of syngas and hydrogen. The formation NiAl2O4, FeAl2O4, MgFe2O4, and Fe2TiO5 were unreadily reduced and unfavorable for the high purity hydrogen production in SR. The NFL, NFZ and NFC presented the better performance than the NFA, NFM and NFT. The catalytic reforming reactions were enhanced significantly by introducing NiO and the supports, while the presence of Ni readily produced higher carbon deposition, which could be alleviated by the addition of steam in FR. The hydrogen purity of all OCs increased to more than 95% in the SR with S/C = 1.4. The top two hydrogen purity in SR for NFZ and NFC were 99.73% and 99.66%, the corresponding hydrogen yield were 1.132 Nm3/kg and 1.165 Nm3/kg, respectively. The NFL exhibited excellent catalytic performance and benefited to produce syngas. The NFZ had the highest oxygen transfer capacity and the lowest carbon deposition. The cyclic stability of NFL and NFZ decreased with the increasing of number of cycles. The NFC is a promising OC in the CLRWS process with the presence of steam, maintained high hydrogen purity and good stability performance in the multiple cycle tests.

Effects of secondary reaction of primary volatiles on oil/gas yield and quality in oil shale pyrolysis

The reaction behaviors of primary volatiles from oil shale pyrolysis were investigated using a two-stage reactor under different in-situ thermal reaction conditions. The reaction parameters of secondary reactor, such as, reactor temperature, atmosphere and residence time, were studied for their effects on the pyrolysis oil/gas yield and quality. The results showed that the reaction temperature had profound influence on the oil and gas yield. The pyrolyzed shale oil and gas yield reduced by 15% and increased by 20% (mass) respectively, with the temperature of 2nd stage reactor increasing from 600 to 650°C under optimized reaction condition of 1st stage. Comparing with nitrogen atmosphere, the liquid oil yield could be enhanced by 5% when steam was added as the reaction atmosphere in the second stage, and the corresponding oil was mainly concentrated in the gasoline and diesel distillations (that is, boiling point <350°C). The GC-MS analysis illustrated that the secondary reaction at the residence time of 0–3 s was mainly pyrolysis while the presence of steam could increase the content of aromatics in the oil and meanwhile suppress the condensation of aromatics. When the residence time was greater than 3–5 s, the secondary reaction was mainly condensation of poly-aromatics, which led to the increase of coke. Meanwhile, the gasoline and diesel oil yield remained stable, and the VGO fractions decreased by about 30%.

Insights and comparison of structure–property relationships in propane and propene catalytic combustion on Pd- and Pt-based catalysts

Hydrocarbon combustion is crucial in emission control applications. Developing efficient catalysts where noble metal use is optimized is imperative in this field. Hydrocarbons with varying molecular structures provide different challenges in this process. In this work, propane and propene were chosen as model compounds to compare the active site requirements for their oxidation on Pd- and Pt-based catalysts. A library of uniform Pd/Pt catalysts prepared from colloidal nanoparticle precursors were used to study several important variables including Pd/Pt composition, support, and phase. The effects of these parameters on activity and stability in the presence of steam were carefully evaluated. Our results show that Pt-rich catalysts perform best for both reactions. However, opposite general trends in rate orders, active phase and stability after aging treatments were observed. These differences arise from the distinct rate-limiting steps and coverage between the two reactions, with propene strongly adsorbing on the noble metal surface, while propane has weaker interactions, resulting in different dominating activation steps. Experimental observations were supported by density functional theory calculations, where the activation barriers to crucial elementary steps were found to be different for the two reactions. The results point to different catalytic requirements to activate the two compounds, highlighting the need to optimize catalysts based on contrasting elements. These findings provide insights that can help engineer efficient catalysts for hydrocarbon combustion and optimize the use of precious noble metals.

Synthesis, characterization, fabrication, and electrochemical performance of transition metal doped LSCTA- as anode candidates for SOFCS

In this work, lanthanum calcium strontium titanates (La0.2Sr0.25Ca0.45TiO3; LSCTA-) are modified with zinc, manganese and chromium (1%; 5%) for their application as solid oxide fuel cell anodes. These compositions are characterized by X-ray diffraction that indicate successful doping of metals onto the parent (LSCTA-) material without a change in the crystallography and leading to a lattice contraction depending on metal element and amount. Fabrication of the electrodes from the LSCTA- on yttria-stabilized zirconia plates is done by air spraying. The electrode performance of the materials is checked under reducing atmosphere (dry; 5% H2/Ar, humidified; 4% H2O/H2) and at different sintering (1200 and 1250°C) and operating (750–650°C) temperatures. The materials sintered at high temperature (1250°C) show comparatively lower polarization resistances (RP) under humidified atmosphere, hence indicate better electrode performance in the presence of steam. Among these doped compositions, polarization resistance is found lower for LSCTA-modified with 1% Zn than all other doped compositions. Overall, the polarization resistance of both LSCTA-with 1% Zn (23 Ωcm2) and 5% Zn (25 Ωcm2) at 750°Cis found lower in comparison to the value reported at 900°C for parent material (45Ωcm2) under humidified atmosphere.

Activated Bio-Carbons Prepared from the Residue of Supercritical Extraction of Raw Plants and Their Application for Removal of Nitrogen Dioxide and Hydrogen Sulfide from the Gas Phase.

The waste materials left after supercritical extraction of hop cones and marigold flowers were tested as precursors of activated bio-carbons. Adsorbents were produced by means of the physical (also called thermal) activation method using CO2 as the gasifying agent. All the activated bio-carbons were tested for the removal of NO2 and H2S from the gas phase under dry and wet conditions. The effects of the type of precursor and the activation procedure on the porous structure development, the acid-base properties of the surface, as well as the sorption capacities of the materials produced were also checked. The final products were bio-carbons of medium developed surface area with a basic surface nature, characterized by their high effectiveness in removal of gas pollutants of acidic character, especially nitrogen dioxide (sorption capacities in the range from 12.5 to 102.6 mg/g). It was proved that the toxic gas removal efficiency depends considerably on the sorption conditions and the activation procedure. All materials showed greater effectiveness in gas removal when the process of adsorption was carried out in the presence of steam.

Support Acidity Improves Pt Activity in Propane Combustion in the Presence of Steam by Reducing Water Coverage on the Active Sites

Support effects in catalysis are important in determining the catalytic activity of supported phases through geometric and electronic effects. Unveiling and quantifying support effects lead to the opportunity to finely tune and optimize the activity of supported catalysts. The study of support effects needs to be conducted in conditions where other important parameters, such as size and composition of the active phase, are not influencing the activity. This requirement is particularly important when the activity is affected by reactants or products that have implications in the reaction mechanism, as is the case of water in hydrocarbon combustion. Here, we present a systematic study on the effects of support acidity and water on propane combustion catalyzed by platinum-based catalysts that reveal support effects beyond the conventional geometric and electronic effects. A set of catalysts prepared from colloidal Pt nanoparticles supported on alumina, silica–alumina, and tungsten oxide-modified silica–alumina with increasing controlled Brønsted acid site density was prepared. We observed a monotonic increase in reaction rate as the same Pt particles were supported on progressively more acidic supports, with an improvement of up to 40 times in reaction rate for the sample with the highest Brønsted acid site density [Pt/WO3(10%)/30% SiO2/Al2O3] compared to the bare Pt/Al2O3 sample. Based on kinetic measurements on samples with different Pt particle sizes, we propose that (i) the metal–support perimeter participates in the reaction, and (ii) the interaction between metal and Brønsted acid sites is responsible for the increase in activity. The origin of such rate increase was found to be related to the enhanced resistance to water poisoning introduced by the acid sites: samples with higher acidity displayed nearly zero water rate order and more stable rates in the presence of steam. Using a Langmuir–Hinshelwood model, the most acidic sample was shown to display the lowest water coverage on the Pt surface. Summarizing all the observations, we propose that the Brønsted acid sites help reduce water coverage on the Pt surface through a spillover-like mechanism, which results in available sites for propane adsorption and activation and thus higher reaction rates in propane combustion. This work highlights how supports play a role not only in modifying electronic and geometric properties of supported phases, but also in the reaction mechanism through active roles in modifying surface coverages.

Co–CeO2 Interaction Induces the Mars–van Krevelen Mechanism in Dehydrogenation of Ethane

Introducing a catalyst for dehydrogenation of ethane (EDH) for steam cracking represents a promising solution with high feasibility to realize efficient ethylene production. We investigated EDH over transition-metal-doped CeO2 catalysts at 873 K in the presence of steam. Ce0.8Co0.2O2 exhibited high EDH activity and selectivity to ethylene (ca. 95%). In the absence of H2O, the catalytic activity dropped rapidly, indicating the promotive effect of H2O on ethylene formation. Catalytic experiments with water isotopes (D2O and H218O) demonstrated that EDH over Ce0.8Co0.2O2 proceeds through the Mars–van Krevelen (MvK) mechanism in which the reactive lattice oxygen in Ce0.8Co0.2O2 contributes to EDH. The consumed lattice oxygen was subsequently regenerated with H2O. X-ray diffraction and in situ X-ray absorption fine structure spectroscopy revealed that cobalt species were mainly present as CoO under EDH conditions and that redox between Co2+ and Co0 proceeded concomitantly with EDH. In contrast with Ce0.8Co0.2O2, no contribution of the lattice oxygen of CoO to EDH was verified in the case of CoO supported on α-Al2O3, which exhibited lower activity than Ce0.8Co0.2O2. Therefore, Co–CeO2 interactions are expected to play a crucially important role in controlling the characteristics of the reactive lattice oxygen suitable for EDH via the MvK mechanism.

Waste tyre char-catalysed in-situ deoxygenation of volatile vapours and production of hydrogen-rich syngas during the pyrolysis of lignite

This paper examined the catalytic performance of tyre char, a waste-derived product on the catalytic pyrolysis of lignite at 600-900 °C, upon the use of different gas environment (i.e. argon versus steam) and different catalyst to lignite mass ratio. All the resultant products (solid, gas and liquid) and spent catalysts have been characterised intensively to elucidate the specific catalytic role of tyre char and the respective mechanisms. As has been confirmed, the tyre char rich in zinc sulphide is a strong Lewis acid that is able to catalyse the upgrading of lignite volatiles via decarbonylation and steam-reforming of the volatile vapours. The former reaction mainly refers to the conversion of aldehydes to alkanes, whilst the latter one is preferentially implemented for the long-chain heavy hydrocarbons that are prone to deposit on the tyre char surface. The presence of steam in the pyrolysis gas environment promotes the steam-reforming of volatiles and steam-gasification of char, but also enhances the acidity strength for the formation of intermediate SO active site that is responsible for the adsorption of O-bearing volatiles and the dissociation of steam. The enhancement of Lewis acid on catalyst surface is also highly sensitive to the mass of catalyst and the extent of its exposure to the O-bearing species including steam and volatile vapours. The use of large quantity such as three times larger than the lignite are essential for the tyre char to remain highly active upon cyclic usage. An extra activation is also essential after each use. In addition, it is confirmed that the catalytic effect of tyre char is profound for the upgrading of volatile vapours released from fast heating of lignite above 700 °C. At 800 °C, the resultant synthesis gas from lignite is also highly rich in H2 and CO than that reported from the upgraded biomass volatiles based on the use of tyre char. A larger H2 yield was also confirmed for the lignites tested here, due to the abundance of long-chain heavy hydrocarbons derived from them.

Influence of Sulfur and Water Vapor on High-Temperature Oxidation Resistance of an Alumina-Forming Austenitic Alloy

The oxidation behavior of alumina-forming alloys was studied after oxidation treatments conducted at 900 °C for 24 h in air or in steam. Alloys with sulfur contents ranging from 1 to 82 ppm in wt% were used. The influence of trace sulfur as well as the presence of steam in the oxidizing atmosphere were investigated. Under oxidation conditions, higher sulfur contents led to higher mass gains and the trend was more pronounced in steam than in air. Oxides were identified by Raman spectroscopy: a thin and continuous α-Al2O3 layer was formed at the metal-oxide interface in all cases. The mass gain differences were caused by other oxides formed at the surface of the samples—mainly spinel and Cr2O3—and in the internal oxidation zone too— mainly α-Al2O3 and θ-Al2O3—indicating that the protectiveness of the alumina layer greatly depends on the sulfur content in the base material and the oxidizing atmosphere. In order to explain this phenomenon, oxide structures were analyzed at various scales using scanning electron microscopy, transmission electron microscopy and nanoscale secondary ion mass spectrometry. Sulfur was detected at metal-oxide interfaces and also in the alumina layer in regions enriched with chromium. In addition, we demonstrate that steam oxidation leads to finer alumina grains as compared to air oxidation. Finally, the relationship between oxidation conditions, nanoscaled structural features and oxidation kinetics is discussed.

Storage Material Effects on the Performance of Ru-Based CO2 Capture and Methanation Dual Functioning Materials

In this study, a systematic investigation on Dual Functioning Materials (DFMs) for the capture and methanation of CO2 is carried out. The attention is focused on the nature of the CO2 adsorbent component (storage material, SM) varying between alkaline (Li, Na, K) and alkaline-earth (Mg, Ca, Ba) metal oxides in combination with Ru, both supported on an Al2O3 support. Combining gas phase reactivity analysis and FT-IR characterization, the samples are characterized in terms of CO2 storage capacity. It is found that all the SM-containing samples adsorb significant amounts of CO2 as carbonate species, with the higher amounts being adsorbed when the more thermally stable species are formed, i.e., when Ca, Ba, or K are employed as SMs. In all cases, the hydrogenation of the adsorbed carbonates to CH4 occurs at lower temperature, if compared to their thermal desorption. However, in the case of Ca- and Ba-based DFMs, resilient carbonates are present on the material surface. It was found that the SMs able to form the more thermally stable carbonates upon CO2 adsorption also showed the best performances in capture/methanation cycles at 350 °C, even if some residual carbonates were left on the DFM after the hydrogenation step. In particular, the following order of reactivity has in fact been observed in terms of CH4 production: Ru–K ≥ Ru–Ba > Ru–Ca > Ru–Na ≫ Ru–Mg ≅ Ru–Li ≅ Ru. The presence of steam and O2 during the capture step has a detrimental effect on the CO2 adsorption for all samples and, as a result, on CH4 production due to the competition of CO2 and water for the same adsorption sites. Thus, only SMs able to form strongly bound carbonates species upon CO2 exposure can retain significant CO2 storage capacity also in the presence of water in the adsorption feed.

Effects of Amine Structures on Oxidative Degradation of Amine-Functionalized Adsorbents for CO2 Capture

A series of adsorbents containing different amines including diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, branched poly(ethylenimine), and spermine were exposed to flowing O₂ at accelerated temperatures of 80 and 100 °C. Herein, we evaluated the structural effects of amines on the stability of CO₂ adsorbents in dry and wet O₂-containing environments. Various techniques were used to characterize the adsorbents. The CO₂ adsorption capacity of the sorbents was drastically reduced after exposure to dry O₂-containing environments. Sorbents modified with amines with a high molecular weight and a long chain of alkyl linkers between amine functional groups exhibited high resistance to O₂. The viscosity of the amines played an important role in the oxidative stability of the amine composites as it affected the mass transfer of O₂ to the amine sites of the composites. Furthermore, we report for the first time that the presence of steam in O₂ medium could suppress or accelerate the oxidative degradation of amine-based CO₂ sorbents depending on the amine structure.

Tar steam reforming during biomass gasification: kinetic model and reaction pathway

In this study, the steam reforming of naphthalene and pyrene as heavy tar model compounds was investigated experimentally in a horizontal tube reactor and theoretically using the CHEMKIN simulation. The experimental results revealed that the reactivity of naphthalene was higher than that of pyrene in the presence of steam. The carbon content converted to soot is a little more than that converted to light gas during tar steam reforming. The kinetic parameters of the overall reaction were determined, and the pre-exponential factor and activation energy were calculated using the experimental data. The comparison of the numerical simulation with the experimental findings exhibited an excellent agreement for the prediction of the light gas products and soot after eliminating the influence of the water–gas shift. Further, the reaction schemes including the reaction pathway and associated kinetics were determined for the steam reforming of these model compounds. Both naphthalene and pyrene exhibited a similar performance during the reaction in the presence of steam. Benzene and naphthalene, representing the precursors of the light gas product, were confirmed to be the dominant intermediate components of naphthalene and pyrene, respectively. The consecutive reactions of these intermediates subsequently resulted in the generation of the light gaseous products.

Experimental and density functional theory study of the synergistic effect between steam and SO2 on CO2 capture of calcium-based sorbents

Calcium looping is a fast-developing second generation CO2 capture technology. In practical looping of Ca-based sorbents, steam and SO2 are naturally present in the flue gas subjected to CO2 capture, due to the combustion of fossil fuels. Until now, the single effect of steam or SO2 has been reported to have a significant impact on the CO2 capture of sorbents. However, there are few studies on the synergistic effect of steam and SO2 on the CO2 sorption characteristics of sorbents, and it is poorly understood. In this study, experiments and DFT calculation are employed to clearly understand the synergistic effect of steam and SO2 on the carbonation behaviors of sorbents. Tests were first performed under typical calcium looping (CaL) conditions with and without the presence of steam and SO2 during the carbonation process. Results indicated that the enhancement of steam on the sulfation is obviously stronger than that on the carbonation as the CaL cycles increased, which is then verified by a series of characterization methods. According to quantitative analysis through DFT calculation, the adsorption energy of SO2 on CaO (100) surface was found to be more than that of CO2 in the presence of steam, indicating the preferential adsorption of SO2 in the presence of H2O molecules on the CaO (100) surface. Therefore, the experimental results were verified and the competitive adsorption mechanism of SO2 and CO2 in the presence of steam during the carbonation process was further understood from microscopic aspect.

Confinement of subnanometric PdCo bimetallic oxide clusters in zeolites for methane complete oxidation

• A strategy of encapsulating PdCo clusters into MFI zeolite channels is developed. • PdCo clusters (0.4–0.6 nm) are encapsulated into sinusoidal channels of MFI zeolite. • Co improves the activity of surface oxygen and modulates electronic state of Pd. • PdCo@MFI exhibits high activity and H 2 O-resistance stability for CH 4 combustion. Supported Pd-based catalysts are widely used for various catalytic transformations, but steam-induced sintering remains a critical issue for industrial application. Here, we report a strategy of encapsulating PdCo bimetallic oxide clusters (0.4–0.6 nm) into sinusoidal channels of MFI zeolite used for methane complete oxidation. The introduction of Co species promotes the activation of surface oxygen species and modulates electronic state of Pd species, effectively enhancing the catalytic performance with the lowest temperature of CH 4 complete conversion obtained at 435 °C in the presence of steam. Meanwhile, the PdCo particle size and catalytic activity are remained on PdCo@MFI after 20 h at 420 °C in the presence of steam, much more stable than that of reference catalysts (PdCo/ZSM-5, drop 19% and PdCo/Al 2 O 3 , drop 22%). The strategy of confining bimetallic clusters into zeolites to enhance the activity and stability broadens the avenue to designing better catalysts for methane complete oxidation.

Effect of Steam on the Tar Reforming during Circulating Fluidized Bed Char Gasification.

In this work, the real tar was introduced into the circulating fluidized bed gasifier by pre-mixing tar and char. The effect of steam on the tar reforming characteristics at both 850 and 900 °C was investigated by combining the analysis of the rate of tar conversion, the change of tar content, and char physical structure. The test results indicated that steam could effectively promote the tar conversion. Therefore, the content of tar in the final gas could be reached as low as 32 mg/Nm3. It was found that the effect of steam on the different components of tar was in difference. Among the various components, polycyclic aromatic substances were more inclined to decompose. The results of BET confirmed that the distribution and structure of pore were obviously developed at the presence of steam, and the abundant pore structure further improved the catalytic performance of the char on the tar conversion in turn.

Kinetics and cyclability of limestone (CaCO3) in presence of steam during calcination in the CaL scheme for thermochemical energy storage

In the present work, we explore the use of steam in the CaCO3 calcination step of the Calcium Looping process devised for thermochemical energy storage (CaL-TCES). Steam produces a double benefit: firstly, it fastens calcination, allowing a reduction of the temperature needed to attain full calcination in short residence times, as those required in practice, resulting in energy savings. This behaviour is justified on the basis of a kinetics study results obtained from a non-parametric kinetic analysis, which demonstrate that the presence of steam during calcination can reduce the apparent activation energy from 175 kJ/mol to 142 kJ/mol with a steam’s partial pressure of 29%. In addition, the results obtained for multicycle CaL-TCES tests show that steam alleviates the deactivation of the sorbent, which is one of the main limiting factors of this technology. This behaviour is explained in terms of the effect of steam on the microstructure of the regenerated CaO. Importantly, the values of residual conversion attained by calcining in steam are higher than those without steam.

Large-scale applications and challenges of adsorption-based carbon capture technologies

This paper introduces adsorption processes with scaled sizes for post-combustion carbon capture, pre-combustion carbon capture, and direct air capture (DAC). Technical characteristics, separation performances, and operating energy consumptions of adsorption-based pilot plants for carbon capture are analyzed. Opportunities and challenges of adsorption-based carbon capture processes in future development are illustrated. Adsorption-based post-combustion carbon capture is a relatively mature technology, which can be applied to retrofitted power plants. However, in order to commercialize this technology, quantities of research and development resources are still needed. Researches on adsorption-based post-combustion carbon capture should focus on the following three aspects: (1) Low-temperature adsorbents with excellent CO2 working capacities, kinetics, and stabilities, (2) low energy consumption cycles using steam purge, and (3) contactors with low gas-solid mass transfer resistances. The warm gas clean-up technology based on pressure swing adsorption (PSA) is a research hotspot for pre-combustion carbon capture. At present, many warm gas clean-up pilot plants are being built worldwide, and in the meantime, some bottlenecks appear. First, the CO2 working capacities of elevated temperature adsorbents are still lower than those of low temperature adsorbents. The recently reported molten salt-promoted magnesium oxide achieves a very high working capacity through the bulk phase chemical absorption, but a carbon capture prototype needs to be established to verify its cyclic stability. Achieving both high purity and high recovery of warm gas clean-up consumes a large amount of high temperature steam. Although multi-train PSA configuration can reduce the energy consumption, it also increases the operating complexity and equipment investment. In addition to CO2, the removal of other impurities such as H2S, COS, HCl, and heavy metals in syngas/reforming gas should be considered. The sorption enhanced reforming with oxy-fuel regeneration process based on high temperature adsorbents can achieve CO2 enrichment in the regeneration reactor. However, pilot plants for this technology are currently lacking, and so detailed techno-economic analysis is still needed to assess its capture cost. Although DAC is a relatively new concept and is still in the early stage for large-scale commercial application, the synergy between DAC and conventional carbon capture technologies can mitigate climate change effects in the long run. The development of DAC technologies needs to pay special attention to the pressure drop problems. Novel gas-solid contactors using structural adsorbents can effectively reduce the power consumption of the fan. Steam purge under subatomospheric pressures reduces the regeneration temperature of DAC, and thus makes the utilization of renewable energy and industrial waste heat for regeneration becoming possible. When steam purge is used, the cyclic stability of the adsorbents should be concerned. For instance, polyamine impregnated adsorbents are prone to amine leakage in the presence of steam. Therefore, the development of hydrothermally stable DAC adsorbents is significantly important.

Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

Thermal modification kinetics and chemistry of poplar wood in dry and saturated steam media

AbstractThis research work presents a modelling strategy to analyse thermal conversion rates of two thermal wood modification processes based on time-temperature superposition method. It gathers in a single study different original and bibliographic experimental works analysing the dry mass variation that occurs during thermal and hydro-thermal wood modification processes. The mass loss kinetic was successfully modelled using a modified Arrhenius approach. The time-temperature superposition method allowed to define for each wood modification process a master curve and its time shift depending on the treatment temperature. The analysis of ventilated oven and saturated steam treatments pointed out the existence of a continuous single kinetic for the ventilated oven which became more complex for saturated steam since a second kinetic stage appeared. This kinetic difference was sustained by infrared spectra chemical analysis which showed that hemicelluloses degraded much faster in presence of steam while lignin degradation occurred in both conditions.

Recent progress in the improvement of hydrothermal stability of zeolites.

Zeolites have been successfully employed in many catalytic reactions of industrial relevance. The severe conditions required in some processes, where high temperatures are frequently combined with the presence of steam, highlight the need of considering the evolution of the catalyst structure during the reaction. This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites.