Cherif Larabi

Low temperature hydrogenolysis of waxes to diesel range gasoline and light alkanes: Comparison of catalytic properties of group 4, 5 and 6 metal hydrides supported on silica–alumina

A series of metal hydrides (M = Zr, Hf, Ta, W) supported on silica–alumina were studied for the first time in hydrogenolysis of light alkanes in a continuous flow reactor. It was found that there is a difference in the reaction mechanism between d0metal hydrides of group 4 and d0 ↔ d2metal hydrides of group 5 and group 6. Furthermore, the potential application of these catalysts has been demonstrated by the transformation of Fischer–Tropsch wax in a reactive distillation set-up into typical gasoline and diesel molecules in high selectivity (up to 86 wt%). Current results show that the group 4 metal hydrides have a promising yield toward liquid fuels.

Thermal decomposition of lignocellulosic biomass in the presence of acid catalysts

Transformation of lignocellulosic biomass to biofuels involves multiple processes, in which thermal decomposition, hydrotreatment are the most central steps. Current work focuses on the impact of several solid acids and Keggin-type heteropolyacids on the decomposition temperature (Td) of pine wood and the characterization of the resulted products. It has been observed that a mechanical mixture of solid acids with pine wood has no influence on Td, while the use of heteropolyacids lower the Td by 100°C. Moreover, the treatment of biomass with a catalytic amount of H3PW12O40 leads to formation of three fractions: solid, liquid and gas, which have been investigated by elemental analysis, TGA, FTIR, GC-MS and NMR. The use of heteropolyacid leads, at 300°C, to a selective transformation of more than 50 wt.% of the holocellulose part of the lignocellulosic biomass. Moreover, 60 wt.% of the catalyst H3PW12O40 are recovered.

Direct thermocatalytic transformation of pine wood into low oxygenated biofuel

Direct catalytic conversion of pine wood under H2 into an organic liquid composed of saturated alkanes and aromatics has been achieved. The resulting organic liquids are easily isolated from the aqueous phase with a yield up to 30 wt%. Importantly, the oxygen content is about 3 wt% and has a higher heating value of 41 MJ kg−1 which is very close to standard diesel (44 MJ kg−1) used in automotive fuels. The multi-functional catalysts comprise well size controlled bimetallic nanoparticles (Cu–Ru) supported on heteropolyacid salts. The residual acidic proton of the heteropolyanion salt combined with bimetallic nanoparticles produced a multifunctional catalyst, featuring depolymerisation, deoxygenation and hydrogenation in a single batch reactor. Current results present an alternative approach to transform lignocellulosic biomass (oxygen content higher than 40 wt%) directly into an organic liquid (oxygen content less than 5 wt%) suitable as additives in biofuels.

Solvent-Free Ring-Opening Metathesis Polymerization of Norbornene over Silica-Supported Tungsten-Oxo Perhydrocarbyl Catalysts.

Ring opening metathesis polymerization (ROMP) of bicyclo[2.2.1]hept-2-ene (norbornene) is carried out over silica-supported catalysts based on tungsten complexes bearing an oxo ligand (1: [(SiO)W(O)(CH2 SiMe3 )3 , 2: [(SiO)W(O)(CHCMe2 Ph)(dAdPO)], dAdPO  2,6 diadamantyl-4-methylphenoxide, 3: [(SiO)2 W(O)(CH2 SiMe3 )2 ]). The evaluation of the catalytic activities of the aforementioned materials in ROMP indicates that at low reaction time (0.5 min), the highest polymer yield is obtained with catalyst 2. However, for longer reaction time (>2 min), complex 3, a model of the industrial catalyst, exhibits a better monomer conversion. The polymers obtained are characterized. Moreover, these catalysts are shown to be rather preferentially selective to give the cis polynorbornene (>65%), characterized by high melting points (≈300 °C). The experimental values of the average molecular weight (Mn ) of polynorbornenes are found to be close to the theoretical ones for the polymers prepared using catalyst 2 and higher for those originated from catalyst 3.

Bifunctional Catalysts Based on Tungsten Hydrides Supported on Silicated Alumina for the Direct Production of 2,3-Dimethylbutenes and Neohexene from Isobutene

Well‐defined bifunctional supported catalysts that comprise tungsten hydride moieties and Brønsted acid sites were prepared successfully. The catalysts showed outstanding activities and selectivities toward the formation of high‐value‐added products, 2,3‐dimethylbutenes and 3,3‐dimethylbutene, through a combination of the metathesis and dimerization of isobutene. The relationship between the physicochemical properties of the catalysts and their activities and selectivities indicated that isobutene conversion increased from 4 to 95 % as a function of the silica content of the silicated alumina (obtained from Sasol). Nevertheless, the selectivity toward branched hexenes showed a volcano‐shaped curve that presented a maximum for the catalyst with 5 wt % silica. Therefore, the control of the support acidity by the silica loading on alumina resulted in an increase of the selectivity toward neohexene.

Silica supported copper nanoparticles prepared via surface organometallic chemistry: active catalysts for the selective hydrogenation of 2,3-dimethylbutadiene

2,3-Dimethylbutadiene can be highly selectively hydrogenated to 2,3-dimethyl-1-butene with a new catalyst based on silica supported copper nanoparticles (Cu-NPs) prepared via surface organometallic chemistry. Mesityl-copper was firmly grafted onto silica and the reduction of the resulting surface species under hydrogen at 350 °C led to well-dispersed Cu-NPs. Prior to catalytic tests, the final catalysts as well as the intermediates were characterised by DRIFT, SS NMR, EPR, TEM, XRD and elemental analyses.