Qian Yao

Towards the sustainable production of pyridines via thermo-catalytic conversion of glycerol with ammonia over zeolite catalysts

In this study, renewable pyridines could be directly produced from glycerol and ammonia via a thermo-catalytic conversion process with zeolites. The major factors, including catalyst, temperature, weight hourly space velocity (WHSV) of glycerol to catalyst, and the molar ratio of ammonia to glycerol, which may affect the pyridine production, were investigated systematically. The optimal conditions for producing pyridines from glycerol were achieved with HZSM-5 (Si/Al = 25) at 550 °C with a WHSV of glycerol to catalyst of 1 h−1 and an ammonia to glycerol molar ratio of 12 : 1. The carbon yield of pyridines was up to 35.6%. The addition of water to the feed decreased the pyridine yield, because water competed with glycerol on the acid sites of the catalyst and therefore impacted the acidity of the catalyst. After five reaction/regeneration cycles, a slight deactivation of the catalyst was observed. The catalysts were investigated by N2 adsorption/desorption, XRD, XRF and NH3-TPD and the results indicated that the deactivation could be due to the structure changes and the acid site loss of the catalyst. The reaction pathway from glycerol to pyridines was studied and the main pathway should be that glycerol was initially dehydrated to form acrolein and some by-products such as acetaldehyde, acetol, acetone, etc., and then acrolein, a mixture of acrolein and acetaldehyde, or other by-products reacted with ammonia to form imines and finally pyridines.

Direct production of indoles via thermo-catalytic conversion of bio-derived furans with ammonia over zeolites

In this study we demonstrate that indoles can be directly produced by thermo-catalytic conversion of bio-derived furans with ammonia over zeolite catalysts. MCM-41, β-zeolite, ZSM-5 (Si/Al = 50) and HZSM-5 catalysts with different Si/Al ratios (Si/Al = 25, 50, 63, 80) were screened and HZSM-5 with an Si/Al ratio of 25 showed the best reactivity for indole production due to the desired pore structure and acidity. Temperature displayed a significant effect on the product distribution. The maximum yield of indoles was obtained at moderate temperatures around 500 °C. The weight hourly space velocity (WHSV) of furan to catalyst investigation indicated that a lower WHSV could cause the overreaction of furan over the catalyst to produce more aniline and pyridines, while a higher WHSV would cause the incomplete reaction of furan. Because ammonia served as both a reactant and a carrier gas, to supply sufficient reactants and keep the desired reaction time, an appropriate ammonia to furan molar ratio was important for furan conversion to indoles. Under optimized conditions, the highest total carbon yield of indoles and their selectivity in the N-containing chemicals were 32% and 75%, respectively. 2-Methylfuran and the mixture of furan and 2-methylfuran were also studied, which demonstrated that more alkyl indoles could be selectively obtained via the coupling reaction of different bio-derived furans. Ring opening of the furan is a more favorable mechanism compared to the Diels–Alder mechanism, and the pyrrole reacting with furan is the more favorable pathway compared to pyrrole reacting with pyrrole based on our experimental and theoretical calculations.

Conversion of levulinic acid and alkyl levulinates into biofuels and high-value chemicals

Levulinic acid (LA) is one of the most important biomass-derived platform molecules and can be produced from both C5 and C6 carbohydrates via tandem dehydration and hydrolysis reactions. Since LA has different functional groups, it would be converted into various compounds by catalyzed reactions. During the past few decades, it has been proved that the conversion of biomass materials into biofuels and chemicals with LA as intermediate is feasible. Alkyl levulinates derived from LA have similar chemical properties to LA and are also used for the synthesis of LA derived molecules. Herein, this review focuses on the transformation of levulinic acid and alkyl levulinate into biofuels and high-valued chemicals, such as γ-valerolactone, 2-methyltetrahydrofurnan, valeric acid/alkyl valerates, 1,4-pentanediol and N-substituted pyrrolidinones. Different homogeneous and heterogeneous catalysts are reviewed and compared. The ligands and additives exhibit a remarkable impact on the distribution of products in homogeneous catalytic systems. Moreover, the catalytic performances of heterogeneous catalytic systems are influenced by numerous factors, such as the size of the metal particles, surface morphology and acid density. In addition, in order to make this review more complete, the production of LA and alkyl levulinates is also included in the manuscript.

Producing pyridines via thermo-catalytic conversion and ammonization of glycerol over nano-sized HZSM-5

In this study, nano-sized HZSM-5 catalysts with different Si/Al ratios were synthesized and employed for producing pyridines from glycerol via a thermo-catalytic conversion and ammonization (TCC-A) process. The catalytic performance of micro-sized HZSM-5 and nano-sized HZSM-5 was studied firstly. The nano-sized HZSM-5 showed better catalytic performance in pyridine production in the TCC-A process due to its smaller particle size. When the nano-sized HZSM-5 (Si/Al = 25) served as the catalyst, and the reaction temperature was about 550 °C with the weight hourly space velocity of glycerol to catalyst at 1 h−1 and the ammonia to glycerol ratio at 12 : 1, the highest yield of pyridines was up to 42.1%, which was much higher than that when using micro-sized HZSM-5 (35.6%) reported before. In addition, nano-sized HZSM-5 also showed a better catalytic performance than micro-sized HZSM-5 in the catalytic conversion of bio-derived furans to produce indoles. After five reaction/regeneration cycles, the catalytic performance of nano-sized HZSM-5 slightly decreased compared with the first run, but was still higher than that of micro-sized HZSM-5.