High pressure cell for edge jumping X-ray absorption spectroscopy : Applications to industrial liquid sulfidation of hydrotreatment catalysts

International audienceA new analytical cell to perform liquid sulfidation of HDS catalysts in industrial conditions was developed. It enables the alternate recording of time-resolved Mo and Co K edges X-ray Absorption spectra of bimetallic catalysts under high pressure (30 bar) and temperature (350°C) during the same reaction. Thanks to this cell, a comparative study of the species formed upon gas (1 bar, 15% H 2 S/H 2) and liquid sulfidation (30 bar, H 2 /gas oil/4% DMDS) of a CoMoP/Al 2 O 3 HDS catalyst was carried out, together with a discussion on the evolution of the concentration profiles upon activation. Different Mo and Co-based chemical species are involved during gas and liquid sulfidation. On one hand, in industrial liquid sulfidation, polymolybdate species are transformed into depolymerized oxides, then into an oxysulfide, a MoS x species and finally into MoS 2. On the other hand, gas sulfidation skips the depolymerization process because of the immediate supply of H 2 S at the beginning of the process and proceeds under a stepwise transformation of oxide into oxysulfide, itself into MoS 3 species and finally into MoS 2. Cobalt species under gas sulfidation goes through a CoS 2 intermediate whereas in liquid sulfidation, it is a 4-fold coordinated Co oxide species. Irrespective to the activation route, mixture of Co 9 S 8 and CoMoS is obtained at advanced sulfidation stage (T> 200°C). Graphical Abstract Quick XAS in situ cell Raman Probe H 2 Gas oil + DMDS 350 C 30 bar Synchrotron radiation Co K edge Mo K edge DMDS decomposition CH 4 H 2 S 232 C 284 C 2 Highlights  A high pressure cell has been developed to study the liquid sulfidation of HDS catalyst by X-ray Absorption Spectroscopy  Co and Mo local orders are studied alternatively during the same reaction  The sulfidation mechanism depends on the activation process  The sulfidation of Co and Mo in liquid phase mainly occurs when DMDS is decomposed into H 2 S between 225°C and 350°C. Gas sulfidation starts at room temperature and is completed at 400°

Structural basis of the signalling through a bacterial membrane receptor HasR deciphered by an integrative approach

Bacteria use diverse signalling pathways to adapt gene expression to external stimuli. In Gram-negative bacteria, the binding of scarce nutrients to membrane transporters triggers a signalling process that up-regulates the expression of genes of various functions, from uptake of nutrient to production of virulence factors. Although proteins involved in this process have been identified, signal transduction through this family of transporters is not well understood. In the present study, using an integrative approach (EM, SAXS, X-ray crystallography and NMR), we have studied the structure of the haem transporter HasR captured in two stages of the signalling process, i.e. before and after the arrival of signalling activators (haem and its carrier protein). We show for the first time that the HasR domain responsible for signal transfer: (i) is highly flexible in two stages of signalling; (ii) extends into the periplasm at approximately 70–90 Å (1 Å=0.1 nm) from the HasR β-barrel; and (iii) exhibits local conformational changes in response to the arrival of signalling activators. These features would favour the signal transfer from HasR to its cytoplasmic membrane partners