Lujiang Xu

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.

The breakdown of reticent biomass to soluble components and their conversion to levulinic acid as a fuel precursor

A biphasic system consisting of THF and water was studied to achieve the integrated conversion of cellulose and hemicellulose in lignocellulosic biomass to levulinic acid. As compared to previous studies using GVL as solvent, the utilization of a lower boiling point solvent, THF, also achieves the simultaneous hydrolysis of C6 and C5 carbohydrates in lignocellulosic biomass, and the results of simultaneous hydrolysis are comparable. Furthermore, it offers an alternative operation procedure after the hydrolysis. A distillation process is not only used to achieve the effective separation of the solid residue from the desired products, but it also helps in the complete isolation of furfural and formic acid from levulinic acid. Consequently, the utilization of by-product formic acid in the hydrogenation of furfural to furfuryl alcohol is explored, and the process is achieved with both model substrates and the feed from the lignocellulosic biomass feedstock. The hydrolysis of furfuryl alcohol gave C5 carbohydrate-derived levulinic acid. We finally explored the integrated conversion with five biomass raw materials, and the total yield of levulinic acid was quite obviously promoted by the additional conversion of pentose.

In situ synthesis of molybdenum oxide@N-doped carbon from biomass for selective vapor phase hydrodeoxygenation of lignin-derived phenols under H2 atmosphere

The vapor phase hydrodeoxygenation (HDO) of lignin-derived phenols under H2 atmosphere has great significance for producing high-quality fuels and commodity chemicals. Herein, we reported a simple, green method to prepare molybdenum oxide@N-doped carbon (MoOx@NC) via in situ pyrolysis of molybdenum precursor preloaded cellulose and demonstrated its catalytic performance for vapor phase HDO of lignin-derived phenols. When the pyrolysis temperature was at 600 °C, the catalyst (MoOx@NC-600) exhibited the best catalytic performance in vapor phase HDO of guaiacol. Through systematically investigating the parameters, such as: reaction temperature, WHSV, residence time, and concentration, the optimal reaction conditions for vapor phase HDO of guaiacol were 450 °C and 1 h−1 with atmospheric H2. The concentration of the feed was 20% in mesitylene, and the residence time was about 3.3 s. The carbon yield of aromatic hydrocarbons was 83.3%, with 65.7% benzene, 15.5% toluene and 2.1% alkylbenzenes. In addition, other lignin-derived phenols were also investigated and desired results were achieved with the MoOx@NC-600 catalyst. Furthermore, MoOx@NC-600 showed good stability due to the N-doped carbon formed on the surface of the MoOx particles. The catalysts were characterized using elemental analysis, AAS, BET, XRD, XPS, TEM, and EDS mapping. The high catalytic performance of MoOx@NC-600 toward lignin-derived phenols HDO can be attributed to the synergistic effect of the carbon supports and Mo5+ (molybdenum oxynitrides), Moδ+ (Mo2N) and Mo4+ on the surface of the MoOx particles.

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.