Nitrogen reduction reaction to ammonia at ambient conditions: A short review analysis of the critical factors limiting electrocatalytic performance

The direct electrocatalytic production of ammonia (NH₃) from N₂ and H₂O at ambient conditions is one of today's chemical challenges to meet the growing industrial demand for ammonia. Despite numerous studies on designing novel catalysts to activate N₂ molecule and elucidating the reaction mechanism, many critical factors (such as gas diffusion and charge transfer limitations that instead promote the side reaction of hydrogen evolution) remain unsolved, suggesting that a breakthrough is needed to improve performance in this challenging reaction. Based on this, we review here recent studies that propose advanced solutions, focusing on: (i) the adoption of a three-dimensional nanoarchitecture of the electrode surface (to favour multi-electron transfer), (ii) the design of cell configuration (including the development of gas diffusion electrodes – GDEs), (iii) the critical aspects of the more efficient lithium-mediated approach in non-aqueous solvents (flooding of the GDE, sustainability of the proton-shuttle system), (iv) new methods for ammonia detection avoiding false positive.     

Electrocatalytic conversion of CO2 to liquid fuels using nanocarbon-based electrodes

Recent advances on the use of nanocarbon-based electrodes for the electrocatalytic conversion of gaseous streams of CO₂ to liquid fuels are discussed in this perspective paper. A novel gas-phase electrocatalytic cell, different from the typical electrochemical systems working in liquid phase, was developed. There are several advantages to work in gas phase, e.g. no need to recover the products from a liquid phase and no problems of CO₂ solubility, etc. Operating under these conditions and using electrodes based on metal nanoparticles supported over carbon nanotube (CNT) type materials, long C-chain products (in particular isopropanol under optimized conditions, but also hydrocarbons up to C8–C9) were obtained from the reduction of CO₂. Pt-CNT are more stable and give in some cases a higher productivity, but Fe-CNT, particular using N-doped carbon nanotubes, give excellent properties and are preferable to noble-metal-based electrocatalysts for the lower cost. The control of the localization of metal particles at the inner or outer surface of CNT is an importact factor for the product distribution. The nature of the nanocarbon substrate also plays a relevant role in enhancing the productivity and tuning the selectivity towards long C-chain products. The electrodes for the electrocatalytic conversion of CO₂ are part of a photoelectrocatalytic (PEC) solar cell concept, aimed to develop knowledge for the new generation artificial leaf-type solar cells which can use sunlight and water to convert CO₂ to fuels and chemicals. The CO₂ reduction to liquid fuels by solar energy is a good attempt to introduce renewables into the existing energy and chemical infrastructures, having a higher energy density and easier transport/storage than other competing solutions (i.e. H₂).     

Reaction Inhibition as a Method for Preventing Thermal Runaway in Industrial Processes

Summary: In this work inhibitors were used to prevent runaway reactions during methylmethacrylate suspension polymerization processes. The main problem that may more frequently occur in chemical reactors, carrying out free radical polymerization reactions, is the loss of temperature control. The addition of an inhibitor during polymerization processes can be considered as a good method to stop or at the least slow down the reaction. In this work two inhibitors were used: hydroquinone and 1,4-benzoquinone in a series of polymerization experiments. In order to identify situations that can lead to a runaway reaction, an early warning detection system based on the divergence criterion was used. When this system signalled an alarm, small amounts of inhibitor were added to the reaction mixture. The results showed that hydroquinone and 1,4-benzoquinone behave slightly differently and the reactor temperature can be kept within safe limits.     

碳基催化剂:为开发下一代纳米工程催化材料开辟新方法(英文)

This essay analyses some of the recent development in nanocarbons (carbon materials having a defined and controlled nano-scale dimension and functional properties which strongly depend on their nano-scale features and architecture), with reference to their use as advanced catalytic materials. It is remarked how their features open new possibilities for catalysis and that they represent a new class of catalytic materials. Although carbon is used from long time in catalysis as support and electrocatalytic applications, nanocarbons offer unconventional ways for their utilization and to address some of the new challenges deriving from moving to a more sustainable future. This essay comments how nanocarbons are a key element to develop next-generation catalytic materials, but remarking that this goal requires overcoming some of the actual limits in current research. Some aspects are discussed to give a glimpse on new directions and needs for RD to progress in this direction.     

Fitting isoperibolic calorimeter data for reactions with pseudo-first order chemical kinetics

The non-linear least squares fitting of the chemical heat flow and the reactor temperature are compared for reactions with pseudo-first order chemical kinetics carried out in an isoperibolic calorimeter operating quasi-isothermally. Both methods give very similar results for the reaction rate constant and enthalpy of reaction but fitting the reactor temperature appears to have some advantages especially when there is an enthalpy of mixing of the reagents.     

The integration of an ultraviolet-visible spectrometer and a reaction calorimeter

A small ultraviolet-visible absorption spectrometer which uses fibre optic coupled immersion probes has been incorporated into a laboratory scale reaction calorimeter. The combined instrument has been tried out using the hydrolysis of acetic anhydride as a test reaction. With the calorimeter operating in the isoperibolic mode good agreement is found for the pseudo-first order reaction rate constant as determined from spectroscopic and calorimetric measurements. Experiments have been made in order to follow the reaction indirectly using optical pH measurements with acid-base indicators. The possibility of determining the temperature dependence of the rate constant in a single experiment has also been investigated. This revised version was published online in July 2006 with corrections to the Cover Date.