Hydrogen delivery through liquid organic hydrides: Considerations for a potential technology

Carrying hydrogen in chemically bounded form as cycloalkanes and recovery of hydrogen via a subsequent dehydrogenation reaction is a potential option for hydrogen transport and delivery. We have earlier reported a novel method for transportation and delivery of hydrogen through liquid organic hydrides (LOH) such as cycloalkanes. The candidate cycloalkanes including cyclohexane, methylcyclohexane, decalin etc. contains 6 to 8 wt% hydrogen with volume basis capacity of hydrogen storage of 60–62 kg/m³. In view of several advantages of the system such as transportation by present infrastructure of lorries, no specific temperature pressure requirement and recyclable reactants/products, the LOH definitely pose for a potential technology for hydrogen delivery. A considerable development is reported in this field regarding various aspects of the catalytic dehydrogenation of the cycloalkanes for activity, selectivity and stability. We have earlier reported an account of development in chemical hydrides. This article reports a state-of-art in LOH as hydrogen carrier related to dehydrogenation catalysts, supports, reactors, kinetics, thermodynamic aspects, potential demand of technology in field, patent literature etc.     

Iron oxide-based honeycomb catalysts for the dehydrogenation of ethylbenzene to styrene

Corning has recently developed a novel extrusion method to make bulk transition metal oxide honeycomb catalysts. One area of effort has been iron oxide-based catalysts for the dehydrogenation of ethylbenzene to styrene, a major chemical process that yields worldwide 20 MM tons/yr. In industry, the monomer is synthesized mostly in radial-flow fixed-bed reactors. Because of the high cross-sectional area for flow and shallow depth of the catalyst bed in these reactors, low reactor pressure gradients are maintained that favors the yield and selectivity for styrene formation. However, the radial-flow design has inherent detractions, including inefficient use of reactor volume and large temperature gradients that decrease catalyst service life. The overall economics of the process can be improved with parallel-channel honeycomb catalysts and axial flow reactors. The simple axial flow design of honeycomb catalysts provides low-pressure drop, while making more efficient use of reactor volume, with better heat and mass transfer characteristics compared to a conventional radial packed bed. An important part of this concept is the ability to fabricate a wide family of dehydrogenation catalyst compositions into honeycombs with the requisite chemical, physical, mechanical, and catalytic properties for industrial use. The ethylbenzene dehydrogenation (EBD) honeycomb catalysts developed by Corning have compositions similar to those commonly used in industry and are prepared with the same catalyst and promoter precursors and with similar treatments.

However, to enable extrusion of catalyst precursors into honeycomb shapes, especially at cell densities above 100 cell/in.², Corning’s process compensates for the high salt concentrations and the high pH of the batch material that would otherwise prevent or impede honeycomb extrusion. The improved rheological characteristics provide the necessary plasticity, lubricity, and resiliency for honeycomb extrusion with sufficient binder strength needed before calcination to the final product. Iron oxide-based honeycombs after calcination are strong and possess macroporosity and high surface area. In bench-scale testing, particular honeycomb catalyst compositions exhibited 60–76% ethylbenzene conversion with styrene selectivity of 95–91%, respectively, under conventional reaction conditions without apparent deactivation or loss of mechanical integrity.     

A novel Pt/Cr/Ru/C cathode catalyst for direct methanol fuel cells (DMFC) with simultaneous methanol tolerance and oxygen promotion

New carbon supported electrocatalysts Pt/Cr/Ru with distinct compositions and preparation methods were studied with the help of different electrochemical and spectroscopic techniques. The purposes of obtaining these catalysts lie on their possibilities towards methanol/oxygen fuel cells. In this sense, the oxygen reduction reaction and methanol oxidation reaction were analyzed using stationary and fluid dynamic methodologies. Pt_7.8/Ru_1.3/Cr_0.5 and Pt_8.0/Ru_2.0/Cr_0.1 were the most interesting prepared substrates, on which the first one shows the best catalytic properties towards methanol oxidation and the second the finest performance towards oxygen reduction reaction. Reaction orders with respect to oxygen for the oxygen reduction reaction were obtained being equal to ½ at potentials lower than 0.80 V for both catalysts. Polarization curves run for this reaction depicted two Tafel slopes, i.e. 0.09 V dec⁻¹ above 0.8 V and 0.20 V dec⁻¹ below 0.8 V for both catalysts. An analysis of the most likely mechanism for the oxygen reduction was proposed on the base of those reaction orders and Tafel slopes.     

Titanium oxide thin film deposited on metallic Cr substrate by RF-magnetron sputtering

In order to develop a colored mirror with hydrophilicity, TiO₂ films are deposited on the Cr and amorphous-TiO₂ substrate. In TiO₂/Cr, a mixed phase comprising of anatase and rutile is formed. In TiO₂/amorphous-TiO₂/Cr, pure anatase phase is obtained. The amorphous-TiO₂ film as interlayer tends to induce micro-columnar-shaped anatase phase. The formation of anatase phase leads to an abrupt decrease of the contact angle by UV-irradiation. Hydrophilic to hydrophobic reconversion by electron-hole recombination is retarded, which seems to be due to pure anatase phase without rutile phase.     

Platinum Nanoparticle Clusters Immobilized on Multiwalled Carbon Nanotubes: Electrodeposition and Enhanced Electrocatalytic Activity for Methanol Oxidation

3D flowerlike Pt nanoparticle clusters are electrodeposited onto multiwalled carbon nanotubes (MWCNTs) by using a three‐step protocol, which is all‐electrochemical and involves a key, second step of a potential pulse sequence. This 3D fractal morphology is in marked contrast to the 2D uniform nanoparticle dispersion of MWCNTs, which is achieved when the second step adopts cyclic voltammetry instead of a potential‐step method. The former is found to exhibit significantly higher electrocatalytic activity and better stability than the latter for oxidation of methanol. These attractive features are attributable to the unique 3D flowerlike structure of Pt nanoparticle clusters on MWCNTs with much higher electrochemically active surface areas. Our work points to a new path for the preparation of 3D Pt/MWCNT nanocomposites, which are promising as electrocatalysts in direct methanol fuel cells.     

Dynamic Simulation and Optimization of a Dual‐Type Methanol Reactor Using Genetic Algorithms

In this investigation, a dynamic simulation and optimization for an auto‐thermal dual‐type methanol synthesis reactor was developed in the presence of catalyst deactivation. Theoretical investigation was performed in order to evaluate the performance, optimal operating conditions, and enhancement of methanol production in an auto‐thermal dual‐type methanol reactor. The proposed reactor model was used to simulate, optimize, and compare the performance of a dual‐type methanol reactor with a conventional methanol reactor. An auto‐thermal dual‐type methanol reactor is a shell‐and‐tube heat exchanger reactor in which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. The proposed model was validated against daily process data measured of a methanol plant recorded for a period of 4 years. Good agreement was achieved. The optimization was achieve by use of genetic algorithms in two steps and the results show there is a favorable profile of methanol production rate along the dual‐type reactor relative to the conventional‐type reactor. Initially, the optimal ratio of reactor lengths and temperature profiles along the reactor were obtained. Then, the approach was followed to get an optimal temperature profile at three periods of operation to maximize production rate. These optimization approaches increased by 4.7 % and 5.8 % additional yield, respectively, throughout 4 years, as catalyst lifetime. Therefore, the performance of the methanol reactor system improves using optimized dual‐type methanol reactor.     

Magnetically recyclable Fe-Ni alloy catalyzed dehydrogenation of ammonia borane in aqueous solution under ambient atmosphere

In this work, we report a very simple method to in situ prepare the Fe_1−xNi_x (x = 0, 0.3, 0.4, 0.5, 0.7 and 1) nano-alloys as the catalysts for H₂ generation from the aqueous NH₃BH₃ solution under ambient atmosphere at room temperature. The prepared nano-alloys possess Pt-like high catalytic activity, especially for the specimen of Fe_0.5Ni_0.5, with which the hydrolysis of NH₃BH₃ would totally complete in only 2.2 min. Moreover, these catalysts can be easily magnetically separated for recycle purpose, and can almost keep the same high activity even after 5 times of recycle under ambient atmosphere. Such alloy catalysts are expected to be useful for fuel cells, metal-air batteries and electrochemical sensors. Moreover, the concepts behind these preliminary results present a wide range of possibilities for the further development of synthesis of air and water-stable magnetic nano-alloys.     

Liquid Holdup in Catalyst‐Containing Pockets of a Modular Catalytic Structured Packing

This paper introduces a simple, first principles‐based model describing the liquid holdup in the catalyst‐containing pockets of Katapak‐SP, a modular catalytic structured packing developed to allow a certain degree of flexibility with respect to the variation in reaction‐to‐separation requirements in a single unit. The basic requirement for the catalyst‐containing pockets in this respect is to be fully filled with flowing liquid which implies that the operating holdup is bound between the static holdup of the catalyst bed as the lower end, and that corresponding to the upper limit, the so‐called catalytic load point. The latter is the liquid load corresponding to the bed saturation point, indicating that excessive liquid will be retained, i.e., will remain in the separation part of the packing element and mix with the liquid leaving the catalyst‐filled pockets at the bottom of the element. Detailed knowledge of the liquid holdup as well as the pattern of the trickling flow is essential because it governs the performance of the reaction part and consequently the hybrid unit as a whole. Both glass and resin (an industrial catalyst) particles were used in conjunction with water and a binary water‐methanol mixture as working fluids. The model predictions for static holdup and the catalytic load agree well with the experiments.     

Simulation and Optimization of an Adiabatic Multi‐Bed Catalytic Reactor for the Oxidation of SO2

A software package was developed for the simulation and optimization of a multi‐bed adiabatic reactor for the catalytic oxidation of SO₂, using a heterogeneous plug flow model. The orthogonal collocation (OC) technique with up to eight collocation points was used for the solution of a nonlinear, two‐point boundary value differential equation for the catalyst particle, and it was shown that the use of the OC technique with two collocation points can describe the system well. Because of the nonlinear behavior of the effectiveness factor along the bed, optimal catalyst distribution between the beds and corresponding inlet temperatures were determined by two methods, including: the use of (1) intrinsic or (2) actual rate of reaction in the optimization criteria. The results showed that for the second case, the minimum amount of the catalyst can be reached at lower temperatures, the amount of catalyst required is always less, and the number of beds is greater than or equal to that of the first case.