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The enzymatic hydrolysis of cellulose toward fermentable glucose is of paramount importance for the production of ethanol or other high-value chemicals from lignocellulosic biomass via the biochemical route. A pretreatment step is usually required that alters the structure and composition of biomass, reduces its recalcitrance, and allows the efficient enzymatic conversion of carbohydrates into sugars. Biomass pretreatment aims mainly at the selective separation of hemicellulose and/or lignin, either as oligomers or as smaller sugar and phenolic molecules, which can be further converted enzymatically or via chemical catalysis to platform chemicals or fuel precursors. In this chapter, a review of the most widely applied pretreatment methods is presented, with the aim of elucidating the role of chemical or biochemical catalysis in this first step of biomass valorization.

Well defined Zn 2 Al-NO 3 /CO 3 and Zn 2 Ga-NO 3 /CO 3 LDH were prepared using typical procedures starting from Zn(NO 3 ) 2 , Al(NO 3 ) 3 and Ga(NO 3 ) 3 . Rh-TPPTS complex was prepared by simple complexation of a Rh precursor [Rh(cod)Cl]2 and TPPTS (3,3′,″-phosphanetriyl benzenesulfonic acid) in water. The heterogeneization of the Rh-TPPTS complex was performed by anionic exchange between Rh-complex and Zn 2 Al-NO 3 /CO 3 or Zn 2 Ga-NO 3 /CO 3 LDH supports. The catalysts structures and the chemical composition were confirmed by XRD analysis, XPS and DRIFT spectroscopy. Triphenylphosphane-substituted Rh heterogeneous catalysts showed good catalytic activity and selectivity in the cycloisomerization of functionalized acetylenic acids.

The potential utilization of various microporous (zeolites H-Y and H-ZSM-5) and mesoporous (amorphous silica-alumina and Al-MCM-41) aluminosilicates as catalysts or active matrices in the cracking of Fischer-Tropsch waxes towards the production of liquid fuels was the subject of this study. Focus was placed on the effect of porous and acidic characteristics of the materials on products yields and properties. Both zeolitic catalysts were very active leading however to different product selectivities. The moderately steamed H-Y catalyst produced more gasoline and less LPGs compared to the H-ZSM-5 catalyst. The relatively high gasoline RON values for both catalysts were attributed to the high yield of iso-alkanes and olefins in the case of the H-Y catalyst and to the high yield of aromatics in the case of H-ZSM-5. The use of mildly acidic Al-MCM-41 type mesoporous materials resulted in relatively low wax conversion activity, while the amorphous silica-alumina catalyst was almost inactive.

In this work we synthesized MFI type zeolites with chromium and gallium. Hydrothermal synthesis was applied using, either aluminum with gallium or chromium sources in 1:1 mole ratios, or impregnation of H-ZSM-5 with the desired metal. The “as synthesized” samples were characterized by XRD, Chemical analysis, SEM-EDS, SSA, ammonia-TPD and subjected to severe steaming, in order to suppress their acidity and consequently decrease the oligomerization capability of the formed catalysts. The catalytic activity of the zeolite samples in propane dehydrogenation was investigated using a fixed-bed continuous-flow glass reactor. The catalytic test results revealed that propylene yield and selectivity over the steamed catalysts increased remarkably (e.g. propylene yield 11% with selectivity of 45%, for H-[Ga/Al]ZSM-5), as a consequence of the suppression of their acidity and therefore of the dramatic decrease of their oligomerization capability. The above results suggest that Cr- and Ga-modified steamed zeolites are promising catalysts for the dehydrogenation of propane to propylene.

The present study focuses on the effect of the metal-modification method (ion-exchange or impregnation) and of the type of dealumination procedure (steaming, AHFS) of zeolite-Y on the quantity, quality and properties of the carbon nanotubes that are formed on the supported iron or cobalt oxides. Severe dealumination of zeolite-Y by steaming, which induced secondary meso/macropores, resulted in significant decrease in the carbon nanotube formation activity of the metal-impregnated zeolite-Y catalysts, while moderate dealumination by ammonium hexafluorosilicate had a less pronounced effect. The micro-Raman spectra revealed the presence of high quality as-grown CNTs with low degree of disordered.

The hydrothermally-stable and acidic MSU-S aluminosilicates assembled from zeolite seeds has been shown to be significantly more active in the cracking of gas-oil, compared to an amorphous commercial silica-alumina catalyst, after moderate steaming pretreatment. When compared to a similarly steamed H-Y based catalyst at constant conversion, the MSU-S catalytic material produced less gasoline and more LCO, while it was more selective for the production of propylene and butylenes, as well as of gasoline range alkenes. The differences in catalytic activity and product selectivity were related to differences in the pore structure/size and in the nature/strength of the acid sites of the tested materials. When the MSU-S materials were tested as FCC catalyst additives, at a concentration level of 8 wt.% on total catalyst weight, they induced higher conversion of gas-oil, mainly due to the increase of LPGs, coke and gasoline range aromatics.