The rising fuel prices, environmental concerns over the emission of greenhouse gases, and the limited availability of fossil fuels led to the current focus on developing alternative fuel sources that are sustainable and environmentally benign. Lignocellulosic biomass, due to its high carbon value, abundance and for being greenhouse gas neutral, is a promising alternative energy resource. Fast pyrolysis of lignocellulosic biomass produces high energy density liquid fuel, called bio-oil, which has the potential as transportation fuel. But, crude bio-oils are chemically complex liquids with high oxygen contents (40 % oxygen content), high viscosity, low pH, low thermal stability, and poor heating values (20 MJ/Kg). Therefore, bio-oils must be substantially upgraded (de-oxygenated) to highly stable, non-corrosive, and high calorific value liquid fuels prior to their use as transportation fuels. This research was conducted to investigate the efficiency of various acid catalysts in upgrading (cracking) the oxygenated pine wood pyrolysis vapors to high quality liquid fuel. Initial catalyst screening studies proved that zeolite acidity and pore structure is essential for effective cracking of pyrolysis vapors. Low space velocities and moderate temperatures were found to be favorable for the deoxygenation of pyrolysis vapors. Various zeolites were tested, of which HZSM-5 with low Si/Al ratio was found to be an effective cracking catalyst. But the use of zeolites resulted in poor liquid yields. Zeolites were promoted with transition metal ions in order to inhibit the secondary cracking reactions occurring on Brönsted acid sites. The metal-promoted biunctional catalysts were found to be the most effective catalysts, among all the catalysts employed in this research, in promoting hydrocarbon forming reactions without adversely affecting the liquid yields. Catalyst coking was unavoidable but the addition of metal ions to zeolites lowered the extent of coking. TG analysis of used catalysts indicated that the catalysts can be regenerated by calcining at 600-650 °C.

Excessive use of fossil fuels shall result in the significant energy problems in the coming century and causes global warming by CO2 emission. Use of petroleum in transportation constitutes the dominant part of total petroleum use. Researches on non-petroleum based, environmentally friendly alternative fuels have been ascended in last decades. Among the alternative fuels, DME has been considered as an attractive fuel alternate due to high cetane number, low PM (particulate matter) and low NOx emission. Synthesis of DME is possible with gasification of biowastes or coal and steam reforming of natural gas. DME is produced in two different methods. In the first method, methanol is formed from the synthesis gas, followed by methanol dehydration to DME. In the second method, called as direct synthesis of DME from synthesis gas, methanol formation and dehydration occurs simultaneously at the same location within the reactor. For the direct synthesis of DME, bi-functional catalysts must be used / one site is responsible for methanol synthesis and other site is responsible for methanol dehydration. Throughout this thesis work, several catalysts were prepared to be used as methanol synthesis component or methanol dehydration component of bi-functional direct DME synthesis catalyst and bi-functional catalysts were also prepared for the direct synthesis of DME from synthesis gas. Materials were characterized by XRD, EDS, SEM, N2 physisorption, and DRIFTS characterization techniques. Activity tests were conducted in a high pressure, fixed bed flow reactor at 50 bar and for the feed gas compositions of H2:CO=50:50 and H2:CO: CO2=50:40:10. Addition of zirconia and alumina promoters, long aging time, calcination temperature of 550 &deg / C and reduction at 250 &deg / C were found to be beneficial in methanol synthesis from the equimolar composition of CO and H2. Precipitated catalysts were usually active and selective to methanol. However, bi-functional co-precipitated catalyst was not successful in situ conversion of methanol into dimethyl ether. Furthermore, tungstosilisic acid impregnated SBA-15 was physically mixed with commercial methanol reforming catalyst and activity results revealed that high DME yield and selectivity were obtained. By physically mixing commercial methanol synthesis and reforming catalysts with &gamma / -Al2O3 and TRC-75(L) in appropriate proportions or by preparing the reactor bed in a sequential arrangement, very high DME yields were obtained and superiority of direct synthesis to conventional two step synthesis was proven. Presence of CO2 in the feed stream not only enhanced the catalytic activity but also utilization of the most important greenhouse gas was accomplished. It was seen that synthesized catalysts are very promising in the direct synthesis of dimethyl ether from synthesis gas.

La thèse étudie le vaporeformage catalytique du méthane avec captage de CO2. Les catalyseurs bi-fonctionnels choisis se composent de nickel, efficace en vaporeformage, de CaO pour la sorption de CO2 et d'aluminate de calcium (Ca12Al14O33) pour permettre une bonne dispersion du métal et de CaO. La méthode de synthèse privilégiée était la méthode d’autocombustion assisté par microondes. Le rapport Ca/Al a été optimisé et un large excès de CaO est nécessaire (75%CaO ; 25%Ca12Al14O33) pour la sorption de CO2. Le reformage du méthane est total dès 650 °C (H2O/CH4 de 1 ou 3) et la sélectivité en hydrogène de 100% durant 7h ou 16h selon les conditions opérationnelles, validant le concept de vaporeformage du méthane assisté par l'absorption de CO2. / This thesis investigates the catalytic steam reforming of methane with CO2 capture. The selected bi-functional catalysts consist of nickel, effective in steam reforming, CaO for sorption of CO2, and calcium aluminate (Ca12Al14O33) to allow good dispersion of metal and CaO. The synthesis method privileged was microwave assisted self-combustion. The Ca/Al ratio was optimized and a large excess of CaO is required (75% CaO, 25% Ca12Al14O33) for the sorption of CO2. Reforming of methane at 650 °C is total (H2O/CH4 1 or 3) and the hydrogen selectivity of 100% during 7h or 16 h according to operational conditions, validating the concept of steam methane reforming with CO2 sorption.