No abstract

The synthesis of efficient molecular water oxidation catalysts (WOCs) and their stable anchoring on suitable electron acceptor supports are crucial, yet challenging, steps for the development of artificial photosynthesis schemes. Here, a highly active diruthenium complex based on the bis­(bipyridyl)­pyrazolate (bbp–) ligand scaffold is anchored on electronically conducting multiwall carbon nanotubes (MWCNTs) using a pyrene group attached to either the pyrazolate backbone (2) or to multiple axial ligand positions (1). High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) show the presence of >75% sp2 hybridization of the MWCNTs and an increase of spectral weight of π–π* transitions upon immobilization of the pyrene-modified ligand or diruthenium complex, supporting pyrene anchoring via π–π interactions. Upon electrochemical oxidation the pyrene groups confined to the MWCNT-modified electrodes are rapidly converted to redox-active surface-bound quinone species. The water oxidation performance of the hybrid systems is studied by cyclic voltammetry and rotating ring disk electrode (RRDE) experiments under acidic aqueous condition (triflic acid, pH 1). Whereas the complex anchored at the backbone position shows higher initial catalytic activity, the complex anchored via four axial ligand positions features a higher stability. X-ray photoemission (XPS) data before and after electrochemical measurements reveal that the chemical structure of the immobilized complex remains intact under catalytic conditions. The results suggest that anchoring of Ru2 complexes by differently located pyrene groups on MWCNTs offers good performance for electron transfer, however, a single pyrene group at the pyrazolate backbone does not provide sufficiently strong surface attachment. The distinct experimental results for MWCNT hybrids with anchored 1 and 2 are further discussed in terms of the preferred attachment position at the pyrazolate-based Ru2 scaffold and the orientation of the catalyst’s active site with respect to the supporting surface.

No abstract

No abstract

Usually large-scale capacities are preferred in process industry because of the economics of scale. However, small capacities bring along several other advantages, which are emphasized especially in on-site production. By producing on-site, the transportation of dangerous chemicals can be avoided. Moreover, smaller on-site production processes also mean a step towards inherently safer technology. Microreactors represent a technology that efficiently utilizes safety advantages resulting from small scale. These safety advantages of microreactors in on-site production are studied in this contribution. Production of peracetic acid is used as a test case. This unstable and explosive chemical is used, e.g. in treatment of municipal wastewater and pulp bleaching. This study is based on comparison of a conventional batch process with the capacity of 170 kg/h and an on-site continuous microprocess producing 10 kg/h peracetic acid. Preliminary design of these processes was carried out. Four different methods were used to analyze the safety of the processes. It was found that the conventional methods for analysis of process safety might not be reliable and adequate for radically novel technology, such as microprocesses. This is understandable because the methods are partly based on experience, which is very limited in the connection of totally novel technology.