Hoda Shafaghat

Catalytic hydrogenation of phenol, cresol and guaiacol over physically mixed catalysts of Pd/C and zeolite solid acids

Highly reactive phenolic compounds of pyrolysis bio-oil are recognized as a major cause of the unpleasant properties of this biofuel. Catalytic hydrodeoxygenation of phenolic compounds of bio-oil is an efficient technique for improving the quality of bio-oil. Dual function catalysts consisting of metal and acid sites are usually used for transformation of bio-oil/bio-oil model compounds to high value hydrocarbons. Metal and acid sites are generally involved in hydrogenation/hydrodeoxygenation and dehydration/hydrocracking/dealkylation/alkylation reaction mechanisms, respectively. In this work, the product selectivity of hydrogenation of phenol, o-cresol, m-cresol and guaiacol was investigated over combined catalysts of Pd/C with zeolite solid acids of HZSM-5 (Si/Al of 30, 50 and 80) and HY (Si/Al of 30 and 60). Catalytic activity and product distribution in the hydrogenation process were affected by the density and strength of zeolite acid sites. HZSM-5 (30) with only weak acid sites showed lower cyclohexane selectivity compared with HZSM-5 (50) and HZSM-5 (80) which had both weak and strong acid sites. HY (30) and HY (60) containing only strong acid sites favored production of cycloketones.

Suppression of coke formation and enhancement of aromatic hydrocarbon production in catalytic fast pyrolysis of cellulose over different zeolites: effects of pore structure and acidity

Rapid deactivation of zeolites caused by high formation and deposition of coke is a great challenge in catalytic conversion of biomass materials into value-added chemicals and fuels. The main purpose of this work was to reduce the formation of both types of thermal and catalytic coke over zeolites. It was revealed that there is a significant interaction between zeolite pore structure and the density of acid sites which could be optimized for reduced coke formation. In this study, catalytic pyrolysis of cellulose was conducted using HZSM-5 (Si/Al: 30), HY (Si/Al: 30) and physically mixed catalysts of HZSM-5 (Si/Al: 30) and dealuminated HY (Si/Al: 327). Coke formation over the physically mixed catalysts was remarkably lower than that over HZSM-5 and HY; the coke contents of HZSM-5, HY and physically mixed catalysts of HZSM-5 and dealuminated HY with a ratio of 70 : 30 wt% were 7.01, 11.47 and 4.82 wt%, respectively. The aromatic hydrocarbon yield was also considerably enhanced over the physically mixed catalysts compared to HZSM-5 and HY; the aromatic hydrocarbon yields achieved over HZSM-5, HY and the mixture of HZSM-5 and dealuminated HY (70 : 30 wt%) were 20.31, 8.91 and 27.01 wt%, respectively. This study shows that the interactive effects of zeolite characteristics such as pore structure and acidity could be taken into account for designing more efficient catalysts to achieve lower coke formation and higher production of desired products.

Effective parameters on selective catalytic hydrodeoxygenation of phenolic compounds of pyrolysis bio-oil to high-value hydrocarbons

Pyrolysis bio-oil is recognized as a renewable and carbon-neutral fuel which could be a potential alternative for depleting fossil fuels. However, bio-oil is highly oxygenated and needs to be upgraded prior to be used as fuel additive. Catalytic hydrodeoxygenation (HDO) is an efficient technique for bio-oil upgrading. The reaction pathway for HDO of bio-oil is unknown since it is a mixture of hundreds of different compounds. The study on mechanism of transformation of these compounds could be helpful to propose an overall pathway for HDO of bio-oil. Phenols which are derived from pyrolysis of lignin fraction of biomass are considered as attractive model compounds for study of bio-oil HDO since they are highly stable in HDO reaction. Reaction pathway and product selectivity in HDO of phenols are highly affected by type of catalyst promoters and supports, catalyst preparation procedure, solvent type, chemicals used as co-feed and operating conditions (i.e., temperature and pressure). The effects of these factors on selective production of high-value hydrocarbons of aromatics and alicyclics from HDO of phenol, cresol, guaiacol and anisole are discussed in this review.

Origin of catalyst deactivation in atmospheric hydrogenolysis of m-cresol over Fe/HBeta

Zeolites are the most common catalysts used for atmospheric deoxygenation of biomass pyrolysis derived feedstocks. The catalytic performance of the zeolite and the yield of deoxygenation greatly depend on the nature of the feedstock. Lignin is the most difficult part of biomass to be deoxygenated and lignin derived phenolic compounds cause rapid deactivation of zeolites. The main purpose of this research was to study the origin of zeolite deactivation in atmospheric deoxygenation of phenolic compounds. Phenol and m-cresol were selected as model compounds for lignin. In order to investigate their effect on zeolite deactivation, catalytic conversion of a mixture of methanol with m-cresol or phenol and a mixture of m-cresol with phenol were carried out over HBeta and Fe/HBeta, respectively. Co-feeding phenol or m-cresol with methanol caused high deactivation of HBeta and significant reduction in the aromatics yield. Meanwhile, these phenols had low reactivity over HBeta. Catalytic performance was enhanced by iron impregnation on zeolite, and Fe/HBeta could considerably convert m-cresol into aromatic hydrocarbons through hydrogenolysis. However, this catalyst was not efficient for deoxygenation of phenol. Strong adsorption of phenol molecules on zeolite acid sites resulting in high formation of coke was the main source of zeolite deactivation which was attenuated by an increase in reaction temperature.