Selective production of high-value fuel via catalytic upgrading of bio-oil over nitrogen-doped carbon-alumina hybrid supported cobalt catalysts.

Bio-oil derived from biomass fast pyrolysis can be upgraded to gasoline and diesel alternatives by catalytic hydrodeoxygenation (HDO). Here, the novel nitrogen-doped carbon-alumina hybrid supported cobalt (Co/NCAn, n = 1, 2.5, 5) catalyst is established by a coagulation bath technique. The optimized Co/NCA2.5 catalyst presented 100 % conversion of guaiacol, high selectivity to cyclohexane (93.6 %), and extremely high deoxygenation degree (97.3 %), respectively. Therein, the formation of cyclohexanol was facilitated by stronger binding energy and greater charge transfer between Co and NC which was unraveled by density functional theory calculations. In addition, the appropriate amount of Lewis acid sites enhanced the cleavage of the C-O bond in cyclohexanol, finally resulting in a remarkable selectivity for cyclohexane. Finally, the Co/NCA2.5 catalyst also exhibited excellent selectivity (93.1 %) for high heating value hydrocarbon fuel in crude bio-oil HDO. This work provides a theoretical basis on N dopants collaborating alumina hybrid catalysts for efficient HDO reaction.

Revealing the crystal facet effect on N2O formation during the NH3-SCR over α-MnO2 catalysts.

The detailed atomic-level mechanism of the effect induced by engineering the crystal facet of α-MnO2 catalysts on N2O formation during ammonia-selective catalytic reduction (NH3-SCR) was ascertained by combining density functional theory (DFT) calculations and thermodynamics/kinetic analysis. The surface energies of α-MnO2 with specific (100), (110), and (310) exposed planes were calculated, and the adsorptions of NH3, NO, and O2 on three surfaces were analyzed. The adsorption energies showed that NH3 and NO molecules could be strongly adsorbed on the surface of the α-MnO2 catalyst, while the adsorption of O2 was weak. Moreover, the key steps in the oxidative dehydrogenation of NH3 and the formation of NH2NO as well as dissociation of NH2 were studied to evaluate the catalytic ability of NH3-SCR reaction and N2 selectivity. The results revealed that the α-MnO2 catalyst exposed with the (310) plane exhibited the best NH3-SCR catalytic performance and highest N2 selectivity, mainly due to its low energy barriers in NH3 dehydrogenation and NH2NO generation, and difficulty in NH2 dissociation. This study deepens the comprehension of the facet-engineering of α-MnO2 on inhibiting N2O formation during the NH3-SCR, and points out a strategy to improve their catalytic ability and N2 selectivity for the low-temperature NH3-SCR process.

Hierarchical porous biochar from plant-based biomass through selectively removing lignin carbon from biochar for enhanced removal of toluene.

This study proposed a simple and green air oxidation (AO) method to prepare hierarchical porous biochar by selectively removing lignin carbon from biochar after the pyrolysis of plant-based biomass, based on the fact that the thermal decomposition temperature in air between lignin carbon and cellulose/hemicellulose carbon was different. Three kinds of biomass with different lignocellulose contents were used, including walnut shell, cypress sawdust and rice straw. The results found that AO treatment could effectively improve the pore structure of the three biochar. The specific surface area of WCO-4, CCO-4 and RCO-4 was 555.0 m2/g, 418.7 m2/g and 291.9 m2/g, respectively, which was significantly higher than those of WC (319.5 m2/g), CC (381.7 m2/g) and RC (69.6 m2/g), respectively. Among these, walnut shell biochar with air oxidation (WCO) had higher surface area of 555.0 m2/g and mesopore volume of 0.116 cm3/g, this was related to its high content of lignin, which could facilitate the formation of mesopores by AO treatment with high selectivity. The toluene adsorption capacity of WCO reached 132.9 mg/g, which increased by 223.4% from that without AO treatment. The kinetics study indicated that the diffusion rates of toluene molecule were improved due to the increased mesopores volume of biochar and micropores also play an important role in the adsorption of toluene. The results demonstrate that AO treatment is a promising method to develop hierarchical porous structure for lignocellulose-rich plant-based biomass with low cost and environmental-friendly, which greatly enhanced the toluene adsorption capacity.

From typical silicon-rich biomass to porous carbon-zeolite composite: A sustainable approach for efficient adsorption of CO2.

Focusing on the high-valued utilization of the widespread silicon-rich waste biomass, a sustainable route by simultaneous utilization of carbon and silicon from silicon-rich rice husk was proposed in this work. Specifically, porous carbon-zeolite composite with hierarchical porous structure of micro/meso pores (carbon) and ultra-microporous pores (Na-X zeolite) was in situ prepared by a facile one-pot method. The obtained porous carbon-zeolite composite (PC2-Z) had a higher yield of 67.66% compared to the porous carbon without silicon (PC2) of 43.33%. Moreover, due to the high ultra-micropore volume of the PC2-Z sample (up to 0.181 cm3/g), it exhibited high dynamic CO2 adsorption capacity of 1.81 mmol/g and CO2/N2 selectivity of 9.80 (1 bar), which were higher than 1.67 mmol/g and 7.01 (1 bar) for PC2, respectively. PC2-Z also showed good regeneration efficiency above 99% after ten cycles. Furthermore, the economic and energy consumption assessment of this utilization route was conducted. Overall, a facile one-pot route was developed to prepare highly efficient composite absorbents from silicon-rich biomass, which can be widely used in different environmental applications.

Air oxidation coupling NH3 treatment of biomass derived hierarchical porous biochar for enhanced toluene removal.

In this study, hierarchical porous biochar was prepared from poplar sawdust by air oxidation coupling with NH3 treatment for the removal of toluene. The results showed that the mesopore volume of the sample with air oxidation (PS‒O2) increased significantly to 0.263 cm3/g from the blank sample (PS, 0.053 cm3/g). This could be attributed to the selective removal of the lignin carbon by air oxidation to develop mesopores in biochar. Following further NH3 treatment (PS‒O2‒NH3), the basic surface chemistry on biochar was improved due to increased basic N-containing groups and decreased acidic O-containing groups, together with the micropore volume also increased to 0.231 cm3/g from 0.186 cm3/g of PS‒O2. The formation mechanism of hierarchical porous structure of biochar was also discussed. The adsorption capacity of PS‒O2‒NH3 for toluene reached 218.4 mg/g at the initial concentration of 820 mg/m3, which was 383.2% higher than that of PS. The adsorption isotherm study indicated that the adsorption process of toluene was monolayered and the maximal adsorption capacity of PS‒O2‒NH3 for toluene could reach as high as 476.2 mg/g. The results demonstrated that air oxidation coupling NH3 treatment is a highly effective method for the preparation of hierarchical porous biochar for enhancing toluene adsorption performance.