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•Shape quality factor describes shapes of UV–vis spectra in aggregations quantitatively.•It decreases when amount of aggregate is small and increase when amount is large.•Its ...relationship with time is a double Gaussian function with high accuracy.•It can describe similarities of shapes of UV–vis spectra conveniently.•It describes aggregation process of conjugated polymer solution at a wavelength range.
We have defined a dimensionless parameter called shape quality factor to describe shapes of UV–vis absorbance spectra during aggregation process of conjugated polymer solutions quantitatively. Time-lapse UV–vis absorbance spectra of poly(3-hexylselenophene) (P3HS) solutions are obtained. Shape quality factors of UV–vis absorbance spectra during the aggregation process of P3HS solutions are calculated. Shape quality factors usually decrease during aggregation process when amount of aggregate is small, and increase when amount of aggregate is large. Relationship between shape quality factor and aggregation time can be fitted by double Gaussian functions. This work provides a simple way to describe shapes of UV–vis absorbance spectra of conjugated polymer solutions quantitatively.
The liquefaction of paulownia in hot compressed water with and without the presence of catalysts such as Fe and Na2CO3 was studied to investigate the catalyst’s effects on the biomass liquefaction ...process. Experiments were conducted in a 1000 ml stainless steel autoclave in the conditions of temperature range of 280–360 °C for 10 min under vacuum, with 60 g biomass and 360 g water, respectively. All the catalysts tested, i.e., Na2CO3 and Fe, were found effective for enhancing the formation of heavy oil products, while they significantly promoted the formation of gas. The experimental results showed that the maximum heavy oil yield rate was 36.34% with Fe catalyst and the minimum solid residue yield was obtained when Na2CO3 was employed as catalyst. The heavy oils from with and without catalyst were characterized by GC–MS and FTIR. The results showed that the oils mainly contained phenol derivatives, ketones, carboxylic acid/ester, benzene derivatives and long-chain alkanes, aldehydes and its derivatives and that employing different catalysts could change the distribution and relative abundance of produced compounds.
This work presents the simulated equilibrium compositions of ethanol steam reforming (SR), partial oxidation (POX) and auto-thermal reforming (ATR) at a large temperature range, steam-to-ethanol and ...oxygen-to-ethanol molar ratios. The simulation work shows that the moles of hydrogen yield per mole ethanol are of this order: SR > ATR > POX. The results are compared with other simulation works and fitted models, which show that all the simulation results obtained with different methods agree well with each other. And the fitted models are in highly consistency with very small deviations. Moreover, the thermal-neutral point in corresponding to temperature, steam-to-ethanol and oxygen-to-ethanol mole ratios of ethanol ATR is estimated. The result shows that with the increasing of oxygen-to-ethanol mole ratio, the T-N point moves to higher temperatures; with the increasing of steam-to-ethanol mole ratio, the T-N point moves to lower temperatures. Furthermore, the energy exchanges of the reforming process and the whole process and the thermal efficiencies are also analyzed in the present work and that the energy demands and generated in the whole process are greater than the reforming process can be obtained. Finally, the optimum reaction conditions are selected.
► The equilibrium compositions simulated by different researchers with different methods are compared. ► The simulation results are fitted with polynomials for convenient reference. ► The energy balance and thermal efficiencies are analyzed. ► The optimum reaction conditions of ethanol POX, SR and ATR for hydrogen production are selected.
Biomass has been proposed to be an alternative source of fuels for industrial applications. The liquefaction of paulownia was studied in hot-compressed water with iron catalyst at temperatures ...ranging from 280 to 360
°C, using a 1000
ml stainless steel autoclave with a magnetic stirrer. With an increase of the reaction temperature, the yield of heavy oil increased and then decreased. The maximum yield of heavy oil of 36.34
wt.% was obtained at 340
°C. The experimental results show that the reaction temperature significantly influenced the process of biomass liquefaction. The liquid products and solid residues produced at various reaction temperatures were analyzed using Fourier transform infrared (FTIR) spectrophotometer and the heavy oil got at 340
°C were analyzed using gas chromatograph with mass selective detector (GC–MS), respectively. The analytical results show that the heavy oil and water-soluble oil is complicated compound. The water-soluble oil mainly contains carbohydrates, acetic acid, alcohols, aldehydes and pyran derivatives. In addition, the heavy oil mainly consists of phenol and its derivatives, ketone, long-chain carboxylic acids/esters, benzene derivatives and long-chain alkanes.
Ni-based catalysts are prone to agglomeration and carbon deposition at high temperatures. Therefore, the development of Ni-based catalysts with high activities at low temperatures is a very urgent ...and challenging research topic. Herein, Ni-based nanocatalysts containing Co promoter with mosaic structure were prepared by reduction of NiCoAl-LDHs, and used for CO2 methanation. When the reaction temperature is 250 °C (0.1 MPa, GHSV = 30,000 mL·g−1·h−1), the conversion of CO2 on the NiCo0.5Al-R catalyst reaches 81%. However, under the same test conditions, the conversion of CO2 on the NiAl-R catalyst is only 26%. The low-temperature activity is significantly improved due to Co which can effectively control the size of the Ni particles, so that the catalyst contains more active sites. The CO2-TPD results show that the Co can also regulate the number of moderately basic sites in the catalyst, which is beneficial to increase the amount of CO2 adsorbed. More importantly, the NiCo0.5Al-R catalyst still maintains high catalytic performance after 92 h of continuous reaction. This is due to the confinement effect of the AlOx substrate inhibiting the agglomeration of Ni nanoparticles. The Ni-based catalysts with high performance at low temperature and high stability prepared by the method used have broad industrial application prospects.
The changing rate of average photon energy ('Eave) can describe the UV-vis absorbance spectra over a wavelength range. During the aggregation process of poly (3-hexylselenophene) (P3HS) and poly ...(3-hexylthiophene) (P3HT) solutions that form J-aggregates, 'Eave always decrease and the relationship between 'Eave and time is an exponential model. 'Eave can predict the time when the aggregation process is completed or how far the aggregation process is from the completion. Hansen Solubility Parameter (HSP) of the solvent can be used to predict 'Eave of some conjugated polymer solutions without doing experiments. ''E0ave (changing rate of 'Eave at the beginning of the aggregation process) has been calculated to reflect the overall changing trend of 'Eave and reflects the compatibility between solvent and solute. Therefore, 'Eave is suitable to describe the aggregation dynamics of conjugated polymer solutions by evaluating the aggregation process in UV-vis absorbance spectra.
Changing rate of average photon energy, UV-vis absorbance spectra, Aggregation process, Conjugated polymer, Poly (3-hexylthiophene), Poly (3-hexylselenophene).
Carbon dioxide (CO2) hydrogenation to methane (CH4) can not only reduce the greenhouse effect but also provide a recyclable source of hydrocarbon fuel. However, traditional Ni‐based catalysts have ...poor low‐temperature activity and the kinetic reaction mechanism for CO2 methanation is not well understood. This work investigates the effects of Na promoter on the catalytic performance, kinetics, and mechanism of Ni/ZrO2 catalysts for the CO2 methanation reaction. Herein, a series of Ni/ZrO2 catalysts with different Na content (0–5 wt%) are prepared by the hydrogel method and used for CO2 methanation. The experimental results show the CO2 reaction rate and Na content have a strong correlation. The addition of Na increases the basic sites and oxygen vacancies, which greatly improves the catalytic activity and selectivity to CH4. Of the studied catalysts, NiNa2.5/ZrO2 exhibits the highest catalytic performance, revealing that a CO2 reaction rate of ∼0.33 moL·gNi–1·h–1, a CH4 selectivity of ∼100% at 300°C, 0.1 MPa, a high GHSV of 30,000 mL·g–1·h–1 are achieved. Kinetic experiments were performed with samples of Ni/ZrO2 and NiNa2.5/ZrO2 at 300°C. These studies suggest that the higher performance of NiNa2.5/ZrO2 is attributed to its lower reaction activation energy. The structure–activity relationships observed herein could provide useful guidance in the design of highly active industrial catalysts.
Abstract
Carbon dioxide (CO
2
) hydrogenation to methane (CH
4
) can not only reduce the greenhouse effect but also provide a recyclable source of hydrocarbon fuel. However, traditional Ni‐based ...catalysts have poor low‐temperature activity and the kinetic reaction mechanism for CO
2
methanation is not well understood. This work investigates the effects of Na promoter on the catalytic performance, kinetics, and mechanism of Ni/ZrO
2
catalysts for the CO
2
methanation reaction. Herein, a series of Ni/ZrO
2
catalysts with different Na content (0–5 wt%) are prepared by the hydrogel method and used for CO
2
methanation. The experimental results show the CO
2
reaction rate and Na content have a strong correlation. The addition of Na increases the basic sites and oxygen vacancies, which greatly improves the catalytic activity and selectivity to CH
4
. Of the studied catalysts, NiNa2.5/ZrO
2
exhibits the highest catalytic performance, revealing that a CO
2
reaction rate of ∼0.33 moL·g
Ni
–1
·h
–1
, a CH
4
selectivity of ∼100% at 300°C, 0.1 MPa, a high GHSV of 30,000 mL·g
–1
·h
–1
are achieved. Kinetic experiments were performed with samples of Ni/ZrO
2
and NiNa2.5/ZrO
2
at 300°C. These studies suggest that the higher performance of NiNa2.5/ZrO
2
is attributed to its lower reaction activation energy. The structure–activity relationships observed herein could provide useful guidance in the design of highly active industrial catalysts.
CO2 methanation can effectively reduce the concentration of CO2 in the air and decrease environmental pollution. Therefore, it is essential to synthesize catalysts with high carbon deposition ...resistance and stability. Herein, the highly stabilized Ni-based catalysts derived from hydrotalcites are prepared by the self-sacrificial template method and used for CO2 methanation. The prepared Ni-based catalysts maintain the morphology of the hydrotalcites precursors and the Ni particles are embedded in the AlOx substrate. The catalyst show high performance at 350 °C, 0.1 MPa and a high space velocity of 30,000 mL g−1 h−1, with the conversion rate of CO2 and selectivity of CH4 reaching 87.5% and 100%, respectively. More importantly, the activity of catalyst does not decrease after continuous reaction for 200 h at 350 °C with different space velocities (30,000 and 60,000 mL g−1 h−1) owing to the confinement of the AlOx substrate, which suppress the undesirable agglomeration and sintering of the Ni particles. This unique mosaic structure has certain reference significance for studying materials with excellent stability at high temperatures.
•The perpared NaY–NiAl-LDHs have sea urchin and tremella morphology.•The catalysts derived from NaY–NiAl-LDHs have unique mosaic structure.•The confinement effects of AlOx inhibite the agglomeration of Ni particles.•Ni nanocatalysts show high carbon deposition resistance and excellent stability.
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•Average photon energy (Eave) depicts energy changes of UV–vis spectra in aggregation.•Eave declines in the aggregation process and can be fitted by exponential models.•Maximum ...aggregation absorbance (ABSmagg) can be fitted by exponential models.•Relationship between Eave and ABSmagg can be fitted by Gaussian models.•Eave can predict the aggregate amount without knowing aggregation time of spectra.
We have defined average photon energy (Eave) to describe energy changes in UV–vis absorbance spectra during the aggregation of conjugated polymer solutions quantitatively. During the aggregation process of P3HS (poly(3-hexylselenophene)), Eave always decreases and maximum aggregation absorbance (ABSmagg) always increases, and relationships between (Eave and ABSmagg) and time are single exponential models. The relationship between ABSmagg and Eave of P3HS is a single Gaussian model, so Eave can be used to predict the amount of aggregate. Eave and ABSmagg of P3HT (Poly(3-hexylthiophene)) follow similar rules of P3HS. This work describes energy changes and predicts the amount of aggregate in UV–vis spectra during the aggregation process.
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