Catalytic dehydration of glycerol to acrolein: catalysts and processes

The valorization of glycerol has been widely studied notably due to the oversupply of the latter from biodiesel production. Among the different upgrading reactions, dehydration to acrolein is of high interest due to the importance of acrolein as an intermediate for polymer industry (via acrylic acid) and for feed additive (synthon for DL-methionine). It is known that acrolein can be obtained by glycerol catalytic dehydration over acid catalysts. Zeolites and heteropolyacid catalysts are initially highly active, but deactivate rapidly with time on stream by coking, whilst mixed metal oxides are more stable catalytic systems but less selective and in addition they require an activation period. In this talk, the strategy we followed is described. It consisted in a parallel approach in which we developed supported heteropolyacid-based catalysts with increased stability and acrolein selectivity by using a ZrO2-grafted SBA-15 playing the role of the support for silico-tungstic acid active phase, as well as a new concept based on a two zones fluidized bed reactor (TZFBR) to tackle the unavoidable deactivation issue of the HPA catalysts. This type of reactor comprises – in one single capacity – reaction and regeneration zones. In the second part of the lecture the REALCAT platform was introduced. REALCAT (French acronym standing for ‘Advanced High-Throughput Technologies Platform for Biorefineries Catalysts Design’) is an highly integrated platform devoted to the acceleration of innovation in all the fields of industrial catalysis with an emphasis on emergent biorefinery catalytic processes. In this extremely competitive field, REALCAT consists in a versatile High-Throughput Technologies (HTT) platform devoted to innovation in heterogeneous, homogeneous or biocatalysts AND their combinations under the ultra-efficient very novel concept of hybrid catalysis.

Cold vapour generation electrothermal atomic absorption spectrometry and solid phase extraction based on a new nanosorbent for sensitive HG determination in environmental samples (sea water and river water)

Mercury is not an essential element for plant or animal life and it is a potential environmental toxic because of its tendency to form covalent bonds with organic molecules and the high stability of the Hg-C bond. Reports estimate a total mercury concentration in natural waters ranging from 0.2 to 100 ng L-1. Due to this fact, highly sensitive methods are required for direct determination of such extremely low levels. In this work, a rapid and simple method was developed for separation and preconcentration of mercury by flow injection solid phase extraction coupled with on-line chemical vapour generation electrothermal atomic absorption spectrometry. The system is based on chelating retention of the analyte onto the mini column filled with a mesoporous silica functionalized with 1,5 bis (di-2-pyridyl) methylene thiocarbohydrazide. The main aim of this work was to develop a precise and accurate method for the determination of the Hg. Under the optima conditions and 120 s preconcentration time, the detection limit obtained was 0.009 μg L-1, with RSDs 3.7 % for 0.2 μg L-1, 4.8 % for 1 μg L-1 and enrichment factor 4, Furthermore, the method proposed has permitted the determination of Hg with a reduction in the analysis time, the sample throughput was about 18 h-1, low consumption of reagents and sample volume. The method was applied to the determination of Hg in sea water and river water. For the quality control of the analytical performance and the validation of the newly developed method, the analysis of two certified samples, TMDA 54.4 Fortified Lake, and LGC6187 River sediment was addressed. The results showed good agreement with the certified values.

In situ characterization of porous VPO catalysts with fibrous structure: Identifying the redox behavior and the stability of active sites

Two VPO materials with fibrillar morphology have been prepared by the aid of electrospinning technique. One is a VPO carbon-supported material (VCF200) with fibrous morphology and very high surface area that is stable under oxidizing conditions up to 350C. The other material is a bulk mixed VPO oxide (VPO500) with fibrous structure obtained after optimizing the calcination of the carbon support in VCF200. Despite it is a bulk oxide material, this material exhibits a high surface area (> 60 m2/g). The redox behavior of both samples was monitored by in situ Raman spectroscopy under oxidation/reduction cycles. For the dehydrated supported sample (VCF200), the pyrophosphate phase (VO)2P2O7 (Raman ~930 cm-1) is detected, which has been described as the active phase (see Figure (a) below). This phase is quite stable since it does not disappear upon subsequent oxidation/reduction cycles. Under reduction conditions at 125C, in consecutive cycles, additional Raman bands appear at ~1090 cm-1 that are characteristic of the αII-VOPO4 phase. On the other hand, the bulk phases show a reversible behavior under redox cycles (Figure (b)). Under reducing conditions, a Raman band appears at ~980 cm-1 (β-VPO phase), whereas under oxidation conditions some segregation to VOx oxides occurs. Nevertheless, this segregation is reversible and the β-VPO phase forms again under reducing conditions. Thus, these results demonstrate that the active VPO phases of these fibrous catalysts are quite stable, and that their structure is reversible under several redox cycles, which make them suitable as oxidation catalysts.