Search

A pure mesoporous SrTiO3 with a honeycomb pore structure is synthesized by the sol-gel method and applied to catalyze transesterification of palm oil with methanol for the biodiesel production. The catalyst is characterized by XRD, CO2/NH3-TPD, N2 adsorption-desorption, SEM-EDX, Raman and XPS to reveal its catalytic performances. The highest FAME yield of 93.14% is achieved in transesterification with the molar ratio of methanol to oil of 15:1 and catalyst concentration of 6 wt% at 170 C for 3 h. Besides, the catalyst is highly tolerant of FFAs and moisture, where the FAME yields of 83.80% and 86.50% are achieved even with the oleic acid and water addition of 10 wt% and 5 wt%. Meanwhile, the catalyst is found to be an effective catalyst for the simultaneous esterification and transesterification. The molecular simulation results show that the Ti sites are more easily attacked by FFAs and the Sr active sites are thus retained for the adsorption of methanol to catalyze transesterification, which explains the bifunctionality of the catalyst.

During the operation of supercritical CO $ _2 $ (sCO $ _2 $ ) turbomachineries, large pressure ratios, supersonic conditions and non-ideal gas fluid dynamic phenomenon may happen, which will decrease the whole cycle efficiencies. Hence non-standard designs for the turbomachineries geometry are needed. Successfully simulations in capturing non-ideal gas fluid dynamics and coupled with optimization algorithm are hard and currently not available in any commercial CFD software. Therefore, the problem of optimizing sCO $ _2 $ turbomachinery is difficult to solve, which has become a major obstacle to obtain compact and high-efficiency sCO $ _2 $ turbomachineries. In this study, a modularized geometry optimizer is developed to obtain the non-standard geometric designs for sCO $ _2 $ turbomachineries. Multiple techniques are applied to this optimizer, include the Nelder–Mead algorithm, Mahalanobis distance and stochastic algorithm. The newly developed optimizer can successfully find the optimum satisfying the objective function under given weighting factors. The computational cost can be reduced through a stochastic algorithm. To validate the optimizer, a convergent–divergent nozzle for air with a target Mach number equal to 2.4 is optimized. Different starting points and combinations of weighting factors are used to create a Pareto front. Adjust the weighting factors for different terms of the objective function leading the optimizer to go to different directions in n-dimensional spaces. Three optimized cases, one is Mach number optimized, one is outlet flow uniformity optimized and the other is compromised case, are picked out and analyzed. The results show that the optimizer can successfully find optimized geometry than the reference case and potentially save computational cost. Due to the modularized characteristics, the components of this optimizer can be replaced with any available techniques, which mean the optimizer can be applied to solve different types of optimization problems.

本研究采用密度泛函理论（DFT）研究了在γ-Fe2O3表面HCl对Hg0的吸附和催化氧化的作用机制。构建了Hg0、HCl、HgCl和HgCl2在γ-Fe2O3(001)表面的吸附模型，分析了HCl对γ-Fe2O3表面催化氧化Hg0的作用机理，并通过反应路径的能量分布测定，研究了γ-Fe2O3表面Hg0的氧化过程。结果表明，Hg0倾向于化学吸附在γ-Fe2O3(001)表面Feoct位。HCl在催化剂表面进行解离吸附，形成吸附态Cl和羟基，从而促进Hg0的吸附。HgCl以分子形式化学吸附在γ-Fe2O3(001)上，并作为Hg0氧化过程的中间体。HgCl2倾向在γ-Fe2O3表面上的平行吸附。同时，HCl在γ-Fe2O3(001)上氧化Hg0遵循L-H机理，即化学吸附的Hg0与解离吸附的HCl反应，且HCl对Hg0的非均相氧化通过两步反应途径进行，即Hg0 (ads)→HgCl(ads)→HgCl2(ads)。

A molecular modeling based on the density functional theory (DFT) and the transition state theory (TST) was performed to investigate the influence of biomass gas CO on the N2O decomposition catalyzed by CaO during reburning in the circulating fluidized bed boiler. The model for N2O adsorption onto the CaO(100) surfaces were constructed; and the processes of the N2O decomposition on the CaO(100) surface and the surface recovery of CaO(100) were investigated. The results illustrate that the energy barrier of N2O decomposition on the CaO(100) surface is much lower than that in homogeneous case, and CaO is therefore able to catalyze the N2O decomposition. The atomic O from N2O decomposition can poison the active sites O atom on the CaO(100) surface, while biomass gas CO can promote the regeneration of the active sites on the surface of CaO(100), which is beneficial for CaO to catalyze the N2O removal.

Calcium oxide is one of the most promising heterogeneous catalysts for biodiesel production. However, an inherent drawback of CaO is the leaching of active species into the reaction solution with the degraded reusability. To strengthen the stability, different supports are composited with the SrO–CaO oxide through the hydrothermal method and mass ratio of SrO to CaO are optimized to get the best outcome of the catalyst. Meanwhile, various characterization methods, including TG, XRD, SEM-EDX, CO2-TPD, XPS, ATR-FTIR and ICP-AES, are used to explore the physicochemical properties of catalysts. The 0.4-SrO-CaO-Al2O3 catalyst shows the best catalytic capability in transesterification of palm oil with methanol to produce biodiesel, where the FAME yield of 98.16% is achieved with the molar ratio of methanol to oil of 18:1 and catalyst concentration of 7.5 wt% at 65 °C for 3 h. Besides, ascribed to the greatly reduced leaching out of the active species, this catalyst presents the satisfying reusability and the FAME yield is slightly decreased to 92.61% for the fifth reused cycle. Therefore, this modification method for SrO–CaO–Al2O3 is feasible for enhancing the catalytic stability in transesterification.

Even though biomass is carbon-neutral renewable energy, the utilization of biomass results in sulfur oxides (SO x ), nitrogen oxides (NO x ) and particles emissions. Biomass briquetting and doping ...

CaO is efficient in catalyzing transesterification for biodiesel production, but its industrial application is inherently restricted by active sites leaching. To address this drawback, CaO is decorated into wollastonite to prepare the stable Ca/wollastonite catalyst. Microwave-assisted transesterification is used to produce biodiesel from palm oil, which effectively accelerates the reaction rate and improves the conversion efficiency. The Ca/wollastonite-0.8 catalyst with the mass ratio of CaO to wollastonite of 0.8 performs well with the fatty acid methyl ester (FAME) yield of 97.59%. Also, this catalyst is highly stable, where the FAME yield of 87.30% could be obtained for the fifth reused cycle. CaO is evenly dispersed on the wollastonite surface and the total basicity is high to 0.281 mmol g−1. Meanwhile, transesterification parameters are optimized by response surface methodology with central composite design (RSM-CCD) and the maximum FAME yield of 98.46% is achieved at reaction temperature of 64.2 °C, molar ratio of methanol to palm oil of 15.54 and mass ratio of catalyst to palm oil of 9.21 wt% for 3 h. Besides, the mass ratio of catalyst to palm oil is the primary variable. Wollastonite is demonstrated to be feasible to enhance the stability of CaO in catalyzing transesterification.

In this paper, a method to fabricate structural N-doped hierarchical porous carbon is proposed. KOH and melamine are found to have synergistically impact on the pore-creating and nitrogen-doping process. The targeted product possesses specific surface area of 2642 m2 g−1 with a highly promoted inner surface area. The specific capacitance increases from 364 to 715 F g−1 at the current density of 1 A g−1 in a two-electrode system using 6 M KOH electrolyte. It also shows the good rate capability (526 F g−1 at 100 A g−1) and cycle performance (98.28% retention after 5000 cycles at 5 A g−1). The energy density reaches 118 W h kg−1 at the power density of 200 W kg−1. The high specific capacitance is mostly derived from the electrical double-layer capacitance, which is a significant advantage compared to the conventional surface doping. The nitrogen atoms stably embedded into the carbon skeleton. N-5 hindered the energy storage process, while N-Q showed obvious impact both on the specific capacitance and cycle performance. All in all, a high-performance electrode material for supercapacitor is provided in this study and it also provides a brand-new idea for the structural doping porous carbon.

Densification and pyrolysis are two methods to upgrade biomass. To avoid ash fusion problems, NH4H2PO4 and Ca(H2PO4)2 were chosen as additives to mix with maize straw to produce biochar briquettes. Potassium transformation mechanisms between additives and biomass in pyrolysis were investigated by XRD, XRF, SEM-EDS, and simulation. Results show that additives accelerate the production of potassium phosphates, which have potential to improve ash fusion temperatures. Addition of additive enhanced deformation temperature (DT) and softening temperature (ST). Multiple linear regression equations between DT/ST and ash compositions were established. In combustion experiment, potassium fixation ratio was increased by additives. Potassium was in the form of high melting products, which finally inhibited fusion phenomenon.

The influence of strontium doping on the adsorption of methanol on calcium oxide surface was investigated by molecular simulation. The model for methanol adsorption onto the CaO(100) and CaO(100)-Sr surfaces was constructed; the adsorption energy and activation energy were then calculated and the density of states was portrayed for the methanol bond on the calcium oxide surface. The methanol activation degrees on the calcium oxide surface before and after strontium doping were then compared by analyzing the Mulliken atomic charge population and deformation density. The results illustrate that the adsorption of methanol onto the calcium oxide surface can be significantly enhanced through the strontium doping; moreover, the enhancement increases with an increase in the doping content of strontium. After doping calcium oxide with strontium, the energy required for methanol activation is reduced; as a result, the strontium doping can also enhance the activation degree of methanol, as methanol is activated upon adsorption onto the calcium oxide surface.

Here a facile and effective method was investigated to regulate the microstructures of porous carbons by adjusting the contents of calcium in precursors. The carbonization characteristics of precursors were characterized by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG), and the results show that the weight loss rates of precursors decrease with the increases of calcium contents. The structures of carbonized samples and their derived porous carbons at the micrometer scale were characterized by Scanning electron microscopy (SEM), and the results show that the structures of carbonized samples change regularly with the increases of calcium contents in precursors, and porous carbons can inherit the structures from their corresponding carbonized samples. The pore characteristics of porous carbons at the nanometer scale were characterized by N2 adsorption and desorption, Barrett Joyner and Halenda (BJH) method and Horvath-Kawazoe (HK) method, and the results show that the existence of calcium in precursors can greatly increase the total pore volumes and specific surface areas of porous carbons derived from precursors, and interestingly it can be noticed that the micropore size distributions of porous carbons in the range of 0.58–10 nm are quite similar.

Here, sodium alginate and calcium alginate which have the same carbon-forming component (alginic acid) and different regulation component (sodium/calcium) were used to prepare porous carbons, and comparisons were made of the microstructures and electrochemical properties of the obtained charcoals. The morphology was characterized by Scanning electron microscopy (SEM), and the results show that porous carbons can inherit plane or concave structures from their corresponding carbonized samples. The Horvath-Kawazoe (HK) method was used to analyze micropore size distributions, and the results show that, under the same mass ratio of potassium hydroxide to carbonized sample (KOH/C), the positions of extreme points on the two curves are similar, but the extreme values are different, and new extreme points appear at larger pore sizes with increases in the KOH/C ratio. The results of cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD) tests show that the capacitance of sodium alginate-derived porous carbon is greater than that of porous carbon derived from calcium alginate when the KOH/C ratios are 2 and 4, and the size relationship is reversed when the KOH/C ratio is 3. The results of cycling performance tests show that the cycle numbers corresponding to the three stages on the two curves are similar under the same KOH/C ratio, but the cycle numbers at the same stage are significantly different under different KOH/C ratios.

3D hierarchical porous carbon is widely accepted as an ideal electrode material for supercapacitor. But template method is a complicated and expensive way to produce material with such a special structure. In this article, a two-step activation method is proposed. Two activating agents: H3PO4 and KOH, are involved in preparation process. By applying this method, the carbonization time can be reduced, the carbonization temperature can be decreased, and the amount of activating agent can be cut down. The specific capacitance of optimal product can reach 366 F g−1 @ 1 A g−1, and even 326 F g−1 @ 10 A g−1 in a two-electrode system using 6 M KOH as electrolyte. The excellent structure endows the product with excellent rate performance (the specific capacitance decreases 18% when the current density increases for 100 times) and cycle performance (95% retention after 5000 cycles). Rational process is benefit for reducing resistance and improving double layer characteristic. The maximum power density can reach 191.90 kW kg−1, and energy density can reach 49.54 W h kg−1. This paper also explores the mechanism of two-step activation and provided a new idea to build 3D hierarchical porous structure by a simple and environmentally friendly way.

The carbon-based heterogeneous acid catalyst is synthesized from bituminous coal through the partial carbonization and sulfonation method and applied to catalyze the esterification of oleic acid with methanol for biodiesel production. Various characterization methods are used to explain catalytic features and molecular simulation is conducted to analyze the promoted mechanism of acid catalyst in esterification. Carbon catalyst, prepared by partially carbonized at 350 °C and sulfonated at 105 °C, catalyzes esterification with biodiesel yield of 98.70%. Transition state analysis implies that acid catalyst reduces the activation energy through providing proton to promote esterification.

Different biomass components have different effects on the microstructures and physicochemical properties of biocarbons. And the properties of biocarbons still need to be further improved. Nanoscale/microscale graphene-like sheets are synthesized with KOH as micropore-forming agent, $$\hbox{Fe}(\hbox{NO}_{3})_{3}\cdot \hbox{9}\,\hbox{H}_{2}\hbox{O}$$ as mesopore-forming agent and graphite catalyst. It is systematically researched to get the effects of biomass components on them. Cane sugar can form flat graphene-like nanosheets with high conductivity. Their performance drops sharply at $$100\,\hbox{A g}^{-1}$$ , indicating that biocarbons need a support of carbon skeleton to operate normally at high current density. Bagasse pith contains amount of cellulose and hemicellulose, which are good for forming pores. Bagasse pith-derived graphene-like sheets possess large specific surface area ( $$2923.58\,\hbox{m}^{2}\,\hbox{g}^{-1}$$ ), high specific capacitance ( $$514.14\,\hbox{F g}^{-1}$$ at $$0.3\,\hbox{A g}^{-1}$$ and $$372.57\,\hbox{F g}^{-1}$$ at $$100\,\hbox{A g}^{-1}$$ ) and high energy density. Due to homogeneous coated doping with graphene-like nanosheets, sugarcane pith-derived graphene-like sheets possess low impedance ( $$\text{R}_{\mathrm{s}}=0.02\,\Omega $$ ), high rate capability (maintained 82.34% from 0.3 to $$100\,\hbox{A g}^{-1}$$ ) and high cycling stability (maintained 101.51% after 5000 cycles), which is better than lots of graphene doping. Sugarcane skin contains more lignin which has hexagonal carbon rings. The graphitization extent of sugarcane skin-derived graphene-like sheets is significantly high. The results provide references to select carbon precursors, and show a novel graphene-like doping method which is suitable for different materials and various fields.

Thermal degradation properties of stearic acid and its esterification derivants of methyl stearate and ethyl stearate are investigated through thermogravimetric analysis. Based on experiments, which are conducted at the temperature heated rates of 10, 15 and 20 K min−1, the iso-conversional methods of Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa are used to calculate the apparent activation energy. Further, the Avrami theory is used to estimate the apparent reaction order. Apparent thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated. Calculations of apparent kinetic and thermodynamic parameters illustrate that thermal activity of stearic acid is distinctly heightened after esterification and the derived derivants are more easily activated. Meanwhile, influences of alcohol type on esterification products are weak. Conclusions from this study make more comprehensive understanding of the thermal events of biodiesel to be favor for its commercial application.

This study presents a novel method to improve the electrochemical performance of porous carbons (PCs) by simply adjusting the elemental composition of their precursors with nitrogen-rich materials as additives. Nitrogen-modified enteromorpha prolifera–based (EP-based) PCs are prepared from EP and urea (or melamine). Overall, compared with the control PC without nitrogen modification, their pore structures and surface chemical properties present similar improvement. When used in supercapacitors, their specific capacitances increase by approximately 22% due to their significant development of mesopores at 2.5–7.0 nm, which increases the effective surface areas. With an appropriate amount of nitrogen-containing or oxygen-containing functional groups maintaining surface wettability, the notable increase of graphitized N improves their conductivity. Due to the higher graphitization degrees, their resistances are reduced. With more mesopores transporting ions, they exhibit excellent high-rate capacitive performance. Moreover, they show remarkable long cycle performance with the specific capacitance retention of larger than 92% after 10,000 cycles.

The influence of the briquetting process on SO2 and NO release characteristics, combustion properties and kinetic characteristics during biomass combustion was investigated. Two biomass (Wheat straw and Tree bulk) and two obtained briquettes were analysed. The briquetting process helps to prevent the release of SO2 and NO. The experimental results show that once the biomass is made into a briquette, when the reaction temperature is 900 ∘C, the sulphur release ratio for TB was reduced from 34.7% to 4.3% and for WS was reduced from 12.4% to 1.6%. When the reaction temperature increases to 1000 ∘C, the sulphur release ratio for TB was reduced from 73.4% to 30.4%, for WS it was reduced from 58.4% to 10.2%. SEM micrographs show that the compact structure of the TB-Briquette and WS-Briquette reduce the rate of SO2 and NO release during combustion. The thermogravimetry confirmed that the combustion performance of WS-Briquette is the best, while the TB-Briquette is the worst. According to the Coats-Redfern method, the fitting was performed at segments of 250 ∘C to 550 ∘C, and the correlation coefficient of the fitting degree was above 0.99. The effective collision rate of WS-Briquette is much higher than that of other briquettes. Compared to BR-1 and BR-2, trying to mix TB with WS to make a compound biomass briquette can enhance the combustion performance of TB-Briquette. The results may guide the upgrading of biomass briquettes technology and benefit the efficient application of biomass briquettes.

The development of electrode materials suitable for aqueous electrolyte and gel electrolyte can greatly promote green energy storage/conversion and contribute to carbon neutrality. Here, N/O codoped layered porous carbons (NOLPCs) are prepared from L-tyrosine by a simple method, and nanoscale NOLPC configuration is constructed by molecular dynamics (MD) simulations. The NOLPCs with layered microstructure can fully contact electrolytes, and show large specific surface area (the highest up to 3221.55 m2 g−1). NOLPC-4.5 for the asymmetric supercapacitor with aqueous electrolyte displays high specific capacitance (512.21 F g−1 at 0.3 A g−1 and 336.43 F g−1 at 100 A g−1) and excellent cyclic stability (95.40 % retention after 5000 cycles). Moreover, it also performs well in the gel electrolyte. The NOLPC configuration has similar microporous structure and elemental composition to the NOLPCs, and the electrolyte can adequately diffuse into its microporous structure. Based on the density functional calculations, it is speculated that the NOLPCs have high electrical conductivity. The NOLPCs, with simple preparation method and excellent energy storage performance, have a good development prospect in green energy storage/conversion. Using MD simulations to construct NOLPC configuration to investigate charging dynamics provides a novel idea for the application of MD simulation in supercapacitors.

A series of carbon catalysts are synthesized through the arylation diazonium salt reduction approach from coal to catalyze esterification of oleic acid with methanol for biodiesel production. Under the activated carbon preparation temperature of 900 °C, mass ratio of 4-aminobenzenesulfonic acid to activated carbon of 6 and arylation temperature of 45 °C, the synthesized carbon catalyst gains the surface area and pore volume of 629.3 m2 g−1 and 0.29 cm−3 g−1, respectively. Besides, the carbon catalyst possesses abundant and strong active sites with the 4-sulfophenyl group density of 0.97 mmol g−1 and acid strength of 0.8

A modified activated carbon material for supercapacitors is prepared via the treatment of gulfweed–based activated carbon with hydrofluoric and nitric acid. The properties of the carbons are characterized by nitrogen adsorption–desorption, scanning electron microscope and Fourier transform infrared spectroscopy. The effect of two–step acid treatment on the electrochemical performance of the activated carbons is investigated by galvanostatic charge–discharge, cyclic voltammetry and AC impedance method. The results show that the hydrofluoric and nitric acid can effectively dissolve the silicon dioxide and other metallic impurities in the carbon materials. The removal of the inorganic impurities contributes to the generation of new pore structure, which provides more transport channels and effective surface area for electrolyte ions and thus improving the electrochemical performance of the carbon materials. Both the capacitance and rate performance improvements of activated carbon are observed after the two–step acid treatment. The gravimetric capacitance of the activated carbons increases from 245 to 310 F g−1 at a current density 0.1 A g−1. The capacitance value of the treated carbon material even remains at 239 F g−1 at a current density of 10 A g−1, which shows excellent high–rate capacitive performance.

Low energy density and ash fusion problem were problems that limit biomass widespread utilization. To avoid these, maize straw (MS) was blended with two additive –NH4H2PO4 (ADP) and Ca(H2PO4)2 (CPM)-respectively, and the production chain of mixing additive-briquetting-pyrolysis was put forward to produce MS char briquettes (MSC, MSC-ADP and MSC-CPM). Ash fusion characteristics of MS char briquettes after combustion was investigated by XRF, XRD, SEM-EDS and simulation. Results show that the softening temperature increased with the enhanced ratio of P2O5/K2O until 0.2, and CaO/K2O until 0.9. The higher amount of CaO and P2O5, the lower amount of K2O, the better ash fusion characteristics. The P2O5 had larger influence on softening temperature. The surfaces of MSC ashes formed at 1000 °C were fusion and smooth in micro observation, while surfaces of MSC-ADP and MSC-CPM ashes were coarse and the particles were much looser. Both SEM-EDS and XRD results illustrated that phosphorus in additives combined with potassium to produce high melting temperature potassium phosphates rather than low melting temperature potassium silicates. The potassium fixation ability of ADP was better than that of CPM. The calcium silicates and calcium phosphates produced by CPM could improve ash characteristics.

A series of heterogeneous acid catalysts are synthesized from bamboo activated carbon through arylation using sulfanilic acid without reductant. Both the catalyst synthesis conditions and parameters for esterification of oleic acid with ethanol are optimized. The heterogeneous acid catalysts are characterized by XRD, FTIR, N2 absorption-desorption, EDX and acid-base neutralization titration. At the molar ratio of benzylsulfonic acid group to bamboo activated carbon of 1, sulfonation temperature of 50 °C and sulfonation duration of 10 min, the heterogeneous acid catalyst presents the mesoporous microstructure with surface area of 225.71 m2 g−1 and pore volume of 0.12 cm−3 g−1, and total acid density of 1.69 mmol g−1. With the catalyst added mass percentage of 12% (relative to the oleic acid mass) and molar ratio of ethanol to oleic acid of 7 at 85 °C for 180 min, esterification efficiency of 96% is achieved, which is higher than 91% of esterification with methanol at 65 °C. Microstructure shrinkage is the main reason for catalyst deactivation, and the regenerated heterogeneous acid supplies the catalytic efficiency of 94%.

Seaweed have different structure and component from terrestrial plant, and the difference can be reserved when it is used for making porous carbon. In this study, Sargassum muticum was token as precursor, KOH and H3PO4 activation were adopted for producing porous carbon. The properties including pore structure, crystalline phases, micromorphology, elementary composition, functional groups and electrochemical performance were characterized and compared with other activated carbons made from terrestrial plants. S. muticum was deemed to be a suitable precursor for pourous carbon. KOH activation method is regarded as a more suitable way to produce porous carbon because the product has good pore structure, high specific surface area (3362 m2 g−1), high graphitization and good electrochemical performance. Porous carbon made by KOH activation also show large power density (64 Wh kg−1) and energy density (21 kW kg−1), good cycle performance (90% reserve after 5000 cycles) and rate capability. Although H3PO4 activation method didn’t show its advantage on S. muticum, it is easier to accomplish as it integrate carbonization and activation into one step, and the produced carbon have higher carbon yield and more functional groups, which means they have potential for faradaic pseudocapacitance after being modified.