Production and stability of low amount fraction of formaldehyde in hydrogen gas standards

Formaldehyde is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687-2 the amount fraction level of formaldehyde present in hydrogen supplied to fuel cell electric vehicles (FCEV) must not exceed 10 nmol mol^?1. The development of formaldehyde standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the FCEV industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 10 μmol mol^?1 with a shelf-life of 8 weeks (stability uncertainty <10%; k = 1), but that formaldehyde degrades into methanol and dimethoxymethane, as measured by FTIR, GC-MS and SIFT-MS. The degradation kinetics is more rapid than predicted by thermodynamics, this may be due to the internal gas cylinder surface acting as a catalyst. The identification of by-products (methanol and dimethoxymethane) requires further investigation to establish any potential undesirable impacts to the FCEV.     

Improved catalytic stability of Pt/TiO2 catalysts for methylcyclohexane dehydrogenation via selenium addition

To improve the catalytic activity of Pt catalysts for methylcyclohexane (MCH) dehydrogenation, which is utilized for hydrogen transportation, the effects of the addition of Se on the performance of Pt/TiO₂ catalysts were investigated. In Se/Pt/TiO₂ catalysts, even a small amount of Se addition (Se/Pt = 0.01) improved the catalyst stability. Se was highly dispersed on the Pt/TiO₂ surface, without volatilizing in a reducing atmosphere at temperatures below 450 °C, and did not form an alloy with Pt. The analysis of adsorption-desorption characteristics revealed that the addition of Se promoted the desorption of products, including the main product, toluene. Moreover, an electron donation effect from Se to Pt was observed by FT-IR measurement after the reduction. The desorption characteristic caused by the electron donation effect suppressed the deterioration of the catalyst and allowed stable catalytic activity toward the MCH dehydrogenation reaction.     

Fast hydrogen evolution by formic acid decomposition over AuPd/TiO2-NC with enhanced stability

Well-dispersed AuPd nanoparticles were immobilized on TiO₂-NC supports derived from NH₂-MIL-125(Ti) and used as highly active, stable catalysts for hydrogen production from formic acid under mild conditions. The highest total turnover frequency, i.e., 3207 h⁻¹, for formic acid dehydrogenation was achieved with Au₂Pd₈/TiO₂-NC-800 as the catalyst at 60 °C; this is 1.4 times that achieved with Au₂Pd₈/TiO₂–C-800 under the same conditions. The excellent performance of the Au₂Pd₈/TiO₂-NC-800 catalyst originates from the high anatase TiO₂ content, pyridinic N and oxygen vacancies in the support, the small size and alloying effect of the AuPd nanoparticles, and the metal–support synergistic effect. Doping the support with N improves the catalyst stability because N prevents metal particle aggregation to some extent. These results provide guidelines for the future development and applications of catalysts based on TiO₂ and metal–organic-framework-derived carbon-based materials.     

Glycerol acetals, kinetic study of the reaction between glycerol and formaldehyde

The acetalization reaction between glycerol and formaldehyde using Amberlyst 47 acidic ion exchange resin was studied. These acetals can be obtained from renewable sources (bioalcohols and bioalcohol derived aldehydes) and seem to be good candidates for different applications such as oxygenated diesel additives. A preliminary kinetic study was performed in a batch stirred tank reactor studying the influence of different process parameters like temperature, feed composition and the stirring speed. A pseudo homogenous kinetic model able to explain the reaction mechanism was adjusted. Thus, the corresponding order of reaction was determined. Amberlyst 47 acidic ion exchange resin showed a fairly good behavior allowing 100% of selectivity towards acetals formation. However, the studied acetalization reaction showed high thermodynamic limitations achieving glycerol conversions around 50% using a stoichiometric feed ratio at 353 K. The product is a mixture of two isomers (1,3-Dioxan-5-ol and 1,3-dioxolane-4-methanol) and the conversion of 1,3-dioxolane-4-methanol into 1,3-Dioxan-5-ol was also observed.     

Solar photocatalytic decomposition of Probenazole in water with TiO2 in the presence of H2O2

The photocatalytic decomposition of Probenazole in water using TiO₂/H₂O₂ under sunlight illumination is studied. The addition of H₂O₂ is effective for the improvement of photocatalytic decomposition of Probenazole with TiO₂. Furthermore, the operating conditions, such as photocatalyst dosage, temperature, pH, sunlight intensity and illumination time are also optimized. The kinetics of photocatalytic decomposition follow a pseudo–first–order kinetic law, and the rate constant is 0.129 min^?1. The activation energy (E_a) is 11.34 kJ/mol. The photocatalytic decomposition mechanism is discussed on the basis of molecular orbital (MO) simulation for frontier electron density.     

Copper-poly (2-aminodiphenylamine) composite as catalyst for electrocatalytic oxidation of formaldehyde in alkaline media

The present work describes the electrocatalytic oxidation of formaldehyde on a copper-polymer modified electrode. The deposition of polymeric film on the surface of carbon paste electrode (CPE) was carried out using consecutive cyclic voltammetry in an aqueous solution of 2-aminodiphenylamine (2ADPA). The transition metal of copper is incorporated into the polymer by electrodeposition of Cu(??) from CuCl₂ acidic solution using potentiostatic technique. Characterization of different modified electrodes was studied using SEM technique and electron probe microanalyzer (EPMA). Cyclic voltammetry experiment of copper-poly(2-aminodiphenylamine) modified carbon paste electrode (Cu/P(2ADPA)/MCPE) in alkaline solution exhibited a number of well-defined anodic and cathodic peaks that are attributed to the Cu/Cu(I), Cu/Cu(II), Cu(I)/Cu(II) and Cu(II)/Cu(III) redox couples. The electrocatalytic oxidation of formaldehyde at the surface of Cu/P(2ADPA)/MCPE was studied by cyclic voltammetry and chronoamperometry methods. This new modified electrode found to be highly active and stable for electrooxidation of the formaldehyde so that the electrocatalytic current density of 25.56 mA cm⁻² was obtained at the potential of 0.63 V. The effects of various parameters such as the copper loading, scan rate and formaldehyde concentration on the electrocatalytic oxidation of formaldehyde were also investigated. Finally, using a chronoamperometric method, the catalytic rate constant (k) for oxidation of formaldehyde was found to be 7.16 × 10⁶ cm³ mol⁻¹ s⁻¹.     

On the long-term stability of Pd-membranes with TiO2 intermediate layers for H2 purification

This work addresses the use of TiO₂-based particles as an intermediate layer for reaching fully dense Pd-membranes by Electroless Pore-Plating for long-time hydrogen separation. Two different intermediate layers formed by raw and Pd-doped TiO₂ particles were considered. The estimated Pd-thickness of the composite membrane was reduced in half when the ceramic particles were doped with Pd nuclei before their incorporation onto the porous support by vacuum-assisted dip-coating. The real thickness of the top Pd-film was even lower (around 3 μm), as evidenced by the cross-section SEM images. However, a certain amount of palladium penetrates in some points of the porous structure of the support up to 50 μm in depth. In this manner, despite saving a noticeable amount of palladium during the membrane fabrication, lower H₂-permeance was found while permeating pure hydrogen from the inner to the outer surface of the membrane at 400 °C (3.55·10^?4 against 4.59·10^?4 mol m^?2 s^?1 Pa^?0.5). Certain concentration-polarization was found in the case of feeding binary H₂–N₂ mixtures for all the conditions, especially in the case of reaching the porous support before the Pd-film during the permeation process. Similarly, the effect of using sweep gas is more significant when applied on the side where the Pd-film is placed. Besides, both membranes showed good mechanical stability for around 200 h, obtaining a complete H₂/N₂ ideal separation factor for the entire set of experiments. At this point, this value decreased up to around 400 for the membrane prepared with raw TiO₂ particles as intermediate layer (TiO₂/Pd). At the same time, complete selectivity was maintained up to 1000 h in case of using doped TiO₂ particles (Pd–TiO₂/Pd). However, a specific decrease in the H₂-permeate flux was found while operating at 450 °C due to a possible alloy between palladium and titanium that is not formed at a lower temperature (400 °C). Therefore, Pd–TiO₂/Pd membranes prepared by Electroless Pore-Plating could be very attractive to be used under stable operation in either independent separators or membrane reactors in which moderate temperatures are required.     

Thermal,mechanical and phase stability of LaCoO3 in reducing and oxidizing environments

Thermal, mechanical, and phase stability of LaCoO₃ perovskite in air and 4% H₂/96% Ar reducing atmosphere have been studied by thermal mechanical analysis (TMA), high temperature microhardness, and high temperature/room temperature X-ray diffraction. The thermal behavior of LaCoO₃ in air exhibits a non-linear expansion in the 100–400 °C temperature range. A significant increase of coefficient of thermal expansion (CTE) measured in air both during heating and cooling experiments occurs in the 200–250 °C temperature range, corresponding to a known spin state transition. LaCoO₃ is found to be highly unstable in a reducing atmosphere. In case where LaCoO₃ was present as a powder, where surface reduction mechanism would prevail, the reduction starts as earlier as 375 °C with a formation of the metallic Co and La₂O₃ at 600 °C. In the bulk form, LaCoO₃ undergoes a series of expansion and contractions due to phase transformations beginning around 500 °C with very intensive chemical/phase changes at 800 °C and above. These expansions and contractions are directly related to the formation of La₃Co₃O₈, La₂CoO₄, La₄Co₃O₁₀, La₂O₃, CoO, and other Co compounds in the reducing atmosphere. Although LaCoO₃ is a good ionic and electronic conductor and catalyst, its high thermal expansion as well as structural, mechanical, and phase instability in reducing environments present a serious restriction for its application in solid oxide fuel cells, sensors or gas separation membranes.     

A novel tubular membrane reactor for pure hydrogen production in the synthesis of formaldehyde by the silver catalyst process

Formaldehyde-based chemistry plays a significant role in the production of different materials. In this work, attempts have been made to revamp a silver catalyzed formaldehyde plant by applying membrane technology. The conventional silver catalyst packed bed reactor was replaced by a shell and tube membrane reactor. A steady-state one-dimensional model was applied to evaluate the performance of the proposed membrane process. The model was validated with experimental results from the plant.The effects of various parameters including reactor pressure, feed temperature, and membrane thickness on the membrane reactor were investigated. Results showed that the effect of feed temperature on production rates was negligible. The increase in pressure and decrease in membrane thickness, however, leads to increase products. The simultaneous production of 100 tonnes/day of formalin 37% (37 wt% formaldehyde in water) and 500 kg/day pure hydrogen achieved by the proposed process. Furthermore, the exiting reactor temperature can be reduced to 420 °C which is significantly lower than the conventional method (650 °C).     

Study of coking and catalyst stability over CaO promoted Ni-based MCF synthesized by different methods for CH4/CO2 reforming reaction

CaO doped Ni/MCF catalysts were prepared by conventional incipient wetness impregnation and sol-gel methods for the study of methane dry reforming reaction. The fresh and used catalysts were characterized using H₂ temperature programmed reduction (H₂-TPR), X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC) and O₂ temperature-programmed oxidation (O₂-TPO). XRD exhibited that CaO and Ni particles are dispersed on the surface of catalyst. The Ni:CaO ratio was adjusted for the improvement of pore textural properties on behalf of enhancement of metal particle dispersion for increased catalytic performance and anti-coking. The catalytic performance and stability of the catalysts for methane dry reforming reaction were studied at 700–750 °C at atmospheric pressure with GHSV of 24000 mL g^?1h^?1 having same feed ratio of CH₄:CO₂ = 1. Experimental results exhibited that catalyst prepared by a sol-gel method showed superior catalytic activity, stability and resisted carbon deposition than catalyst prepared incipient wetness impregnation method. Among all tested catalysts 9CaO 9Ni/MCF catalyst remained the best for catalytic performance and anti-coking activity due to higher metal dispersion with small metal particles, as well as the synergetic effect between CaO and Ni. During 75 h stability test over the catalyst 9CaO 9Ni/MCF the CH₄ and CO₂ conversion remained 91% and 99% respectively.     

Water splitting catalysis beginning with FeCo2S4@Ni(OH)2: Investigation of the true catalyst with favorable stability

Highly active and earth-abundant dual functional electrocatalyst have been developed to resolve energy conversion and storage from water splitting. Herein, for the first time, synthesis of morphology-controllable for the electrocatalytic active Ni(OH)₂ nanosheets deposited on the periphery of FeCo₂S₄ nanorods on the porous nickel foams was designed through two step hydrothermal process. For water splitting, FeCo₂S₄@Ni(OH)₂/NF-3h//FeCo₂S₄@Ni(OH)₂/NF-3h required cell voltage of 1.52 V to drive 20 mA cm⁻², which is one of the smallest value reported compared with previous literature for electrochemistry water splitting through a large number of literature research. Density functional theory calculations and experimental characterization are done to calculate the surface adsorption energy of water molecules on the catalyst surface and explore the hydrogen evolution mechanism of synergistic catalysis. What is noteworthy is that FeCo₂S₄@Ni(OH)₂/NF-3h remain a current intensity of 15 mA cm⁻² for 140 h in 1.0 M KOH solution with a slight increment of the overpotential.     

Activity and stability of non-precious metal catalysts for oxygen reduction in acid and alkaline electrolytes

The activity and stability of non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in both acid and alkaline electrolytes were studied by the rotating disk electrode technique. The NPMCs were prepared through the pyrolysis of cobalt-iron-nitrogen chelate followed by combination of pyrolysis, acid leaching, and re-pyrolysis. In both environments, the catalysts heat-treated at 800-900 °C exhibited relatively high activity. Particularly, an onset potential of 0.92 V and a well-defined limiting current plateau for the ORR was observed in alkaline medium. The potential cycling stability test revealed the poor stability of NPMCs in acid solution with an exponential increase in the performance degradation as a function of the number of potential cycling. In contrast, the NPMCs demonstrated exceptional stability in alkaline solution. The numbers of electron transferred during the ORR on the NPMCs in acid and alkaline electrolytes were 3.65 and 3.92, respectively, and these numbers did not change before and after the stability test. XPS analysis indicated that the N-containing sites of catalysts are stable before and after the stability test when in alkaline solution but not in acid solution.     

Investigation of plasmonic Cu with controlled diameter over TiO2 photoelectrode for solar-to-hydrogen conversion

Plasmonic metal nanoparticles (NPs) have been used to improve the solar-to-hydrogen conversion efficiency. Relative to Au and Ag, Cu is cheaper and more abundant. In the present work, Cu NPs with the controlled diameter were deposited on TiO₂ nanotube arrays (TNTAs) by using a pulse electrochemical deposition method. When the deposition was cycled 3600 times, the size of Cu NPs can be tuned to approximately 30 nm with the most uniform distribution, resulting in the remarkable characteristic peak of surface plasmon resonance and higher photocurrent density. The hydrogen production rates remained unchanged during irradiation (AM 1.5, 100 mW/cm²) of 2 h, indicating a good stability of the resultant Cu/TNTAs electrode. The photoelectrochemical performances of as-prepared Cu/TNTAs can also be comparable to those of Ag/TNTAs electrode fabricated by the same method.     

Electrocatalytic performance of TiO2 with different phase state towards V2+/V3+ reaction for vanadium redox flow battery

In this paper, titanium dioxide (TiO₂) nanoparticles were employed as catalysts towards V²⁺/V³⁺ redox couple of vanadium redox flow battery (VRFB). The effect of TiO₂ phase on the electrocatalytic performance for negative couple was systematically investigated. The electrochemical properties of TiO₂ with different phase were assessed via cyclic voltammetry and electrochemical impedance spectroscopy by using AB as conductive agent. Obtained from the results, anatase TiO₂ (α‐TiO₂) exhibits superior electrocatalytic activity to rutile TiO₂ (γ‐TiO₂). The VRFB cell performs well at discharge capacity, voltage efficiency, and energy efficiency by employing α‐TiO₂‐modified negative electrode with current density varying between 50 and 100 mA cm^?2. The discharge capacity of α‐TiO₂‐modified cell with vanadium ion concentration of 1.6 M comes up to 113.5 mA h at 100 mA cm^?2 current density, which is increased by 39.1 mA h after modification for negative electrode. Moreover, the corresponding energy efficiency increases by 7.5% after modification of α‐TiO₂. Experimental results show that TiO₂ is an ideal catalyst for VRFB. Moreover, α‐TiO₂ demonstrates superior electrocatalytic performance to γ‐TiO₂ towards V²⁺/V³⁺ reaction.     

Structural and catalytic studies of Mg1-xNixO nanomaterials for gasification of biomass in supercritical water for H2-rich syngas production

Nowadays, catalytic supercritical water gasification (SCWG) is undoubtedly used for production of H₂-rich syngas from biomass. The present study reported the synthesis and characterisation of Mg_1-xNi_xO (x = 0.05, 0.10, 0.15, 0.20) nanomaterials that were obtained via self-propagating combustion (SPC) method, and catalysed the SCWG for the first time. It had found that increased the nickel (Ni) content in the catalyst reduced the crystallite size, thus, increased the specific surface area, which influenced the catalytic activity. The specific surface area followed the order of Mg_0.95Ni_0.05O (36.2 m² g⁻¹) < Mg_0.90Ni_0.10O (58.9 m² g⁻¹) < Mg_0.85Ni_0.15O (63.6 m² g⁻¹) < Mg_0.80Ni_0.20O (67.9 m² g⁻¹). From the Rietveld refinement, the Ni that was successfully partial substituted in the cubic crystal structure of MgO resulting in a cell contraction which ascribed the reduction of crystallite size. Increased the amount of Ni also narrowed the pore size distribution ranging between 4.17 nm and 6.23 nm, as well as increased the basicity active site up to 5741.0 μmol g⁻¹ at medium basic strength. All the synthesised nanocatalysts were catalysed the SCWG of OPF (oil palm frond) biomass. Among them, the mesoporous Mg_0.80Ni_0.20O nanocatalyst exhibited the highest total gas volume of 193.5 mL g⁻¹ with 361.7% increment of H₂ yield than that of the non-catalytic reaction.     

Influence of different carbon nanostructures on the electrocatalytic activity and stability of Pt supported electrocatalysts

Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric–sulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF ? Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity.     

Operating characteristics and performance stability of 5 W class direct methanol fuel cell stacks with different cathode flow patterns

In this study, 5 W class direct methanol fuel cell (DMFC) stacks using the flow field patterns of serpentine, parallel, and square spot are fabricated to compare how well they are capable of mass transport and water removal in the cathode. The stability of the stack is predicted through the simulation results of the flow field patterns on the pressure drop and the water mass fraction in the cathode of the stack. It is then estimated through the performance and the voltage distribution of the stack. According to the simulation results, although the square spot pattern shows the lowest pressure drop, the square spot pattern has much higher water mass fraction in the central region of the channel compared to the other flow field patterns. In accordance with the results, a square spot pattern for the stack-SSMA exhibits very poor water removal capabilities, leading to water flooding near the channel exit. In contrast, the performance stability of a stack-SPMA is comparable to the stack-SSMM.     

On the synthesis of nanostructured TiO2 anatase phase and the development of the photoelectrochemical solar cell

Unlike the rutile; the anatase phase of TiO₂ has not been extensively employed for fabrication of PEC cells primarily due to the difficulty in the synthesis of a stable anatase structural variant. The present investigation is focused on the synthesis of the anatase phase and its use as a photoelectrode of high efficiency PEC Solar Cells. TiO₂, in the nanostructured form, has been prepared by the hydrolysis of Titanium (IV) isopropoxide solution. The nanostructured TiO₂ (anatase) stable phase has been synthesised by sintering the synthesised film at ∼500°C with a heating rate of 1°C/min for a duration of 3 h in argon. The films of nanostructured TiO₂ anatase phase have been used as photoelectrodes in PEC solar cells.An improvement in TiO₂(ns) anatase phase photoelectrode carried out in the present work corresponds to admixing In₂O₃ to improve the spectral response. It has been found that admixing In₂O₃ with TiO₂(ns) anatase phase improves the solar spectral response. The structural, microstructural, optical, and photoelectrochemical properties of the TiO₂(ns) anatase phase and TiO₂(ns) anatase-In₂O₃ photoelectrode have been studied. The response of TiO₂(ns) anatase phase bearing photoelectrode based PEC solar cell corresponds to V_OC ≈ 460 mV, I_SC ≈ 2.4 mA/cm² and for its In₂O₃ doped version, these are V_OC ≈ 640 mV and I_SC ≈ 10.4 mA/cm².     

Preparation of a stable nanocomposite phase change material (NCPCM) using sodium stearoyl lactylate (SSL) as the surfactant and evaluation of its stability using image analysis

In this study, a new method was proposed for the preparation of a stable Al₂O₃-paraffin nanocomposite phase change material (NCPCM). Sodium stearoyl lactylate (SSL) was used as the surfactant to improve the dispersion of Al₂O₃ nanoparticles (2.5, 5, 7.5, and 10 wt.%) in paraffin with a SSL/Al₂O₃ mass ratio of 1:3.5. After preparation, one group of the samples was placed in an incubator at a temperature of 60 °C for one week to evaluate its stability during the time elapsed. The other was left alternately in two incubators, one at 60 ^°C and the other at 25 ^°C over time intervals of 1 h in order to evaluate the stability of the sample after given numbers of melting/freezing cycles. This latter treatment has been seldom ever reported elsewhere. For NCPCM stability evaluation, the samples were broken into two parts equal in volume and the change ratios of surface layer Al³⁺ concentration are determined. Also, image analysis is used for evaluating the stability of nanofluids. The results obtained from the two methods are found to be in good agreement. Image analysis is, therefore, proposed as a nondestructive method with good accuracy, especially for evaluating the stability of high concentration nanofluids.