The production of lactic acid (LA) from glycerol in alkaline medium was investigated using Cu catalysts supported on CaO, MgO and
x
CaO/MgO (
x
= 5, 10, 15 wt%), employing a continuous flow reaction ...system over a period of 30 h. In addition to assessing the effect of the composition of the catalytic support, the influence of the temperature (200-260 °C), NaOH/glycerol molar ratio (0.5-1.5), hydroxide type (NaOH and KOH), as well as the influence of concentration (10 and 20 vol%) and purity of glycerol was investigated. The catalysts were prepared by a wet impregnation method and characterized by XRF, XRD, N
2
adsorption-desorption, H
2
-TPR and CO
2
-TPD. The catalytic tests showed that the use of NaOH results in higher yields to LA. Cu catalysts supported on
x
CaO/MgO exhibited better catalytic performance than the CuCa and CuMg catalysts. The LA yield increases with the increase of the reaction temperature from 200 to 240 °C, and then decreases with a subsequent increase to 260 °C. NaOH/glycerol molar ratios greater than 1.25 are not necessary, since high yield to LA (96.9%) was obtained in the catalytic test performed using a molar ratio of 1.25. The catalysts showed excellent stability without evidence of deactivation over the evaluated period.
The production of lactic acid (LA) from glycerol in alkaline medium was investigated using Cu catalysts supported on CaO, MgO and
x
CaO/MgO (
x
= 5, 10, 15 wt%), employing a continuous flow reaction system over a period of 30 h.
The environmental impact and the forecasted scarcity of fossil fuels have intensified research on renewable energy sources. Hydrogen is a versatile energy carrier that can be produced from renewable ...sources and plays a key role in achieving global decarbonization targets. Biogas, produced by anaerobic digestion of organic compounds, is rich in methane and carbon dioxide and can be used to produce renewable hydrogen by dry reforming. This review focuses on the recent advances in Ni-based catalysts for biogas reforming. The effect of supports and promoters on catalyst activity, stability, and resistance to carbon deposition will be systematically discussed. This review provides a better understanding of the influence of the synthesis method, metal-support interaction, acid/base sites, and oxygen mobility on catalytic activity. Special emphasis will be given to the development of core-shell structure catalysts and bimetallic catalysts of Ni with other transition metals and noble metals.
Nickel catalysts derived from hydrotalcite-like compounds, with 10 and 20 wt.% NiO loading, were prepared and tested in steam reforming of different tar model compounds: benzene, toluene and ...naphthalene. Naphthalene was used in toluene solution. The catalysts were evaluated in terms of activity with temperature and deactivation with time, using a steam/carbon ratio of 1.5. The catalysts presented similar behavior, with slightly higher conversions for the catalyst with 10% NiO in benzene and toluene reforming. H sub(2) formation was much lower than that predicted by thermodynamics, with CO sub(2) as the main product at low temperatures and CO at high temperatures. Naphthalene is much more difficult to be converted, and inhibits the toluene reforming. Both catalysts showed good stability with time on stream despite the high amount of carbon deposit and Ni sintering. The amount and morphology of the coke are dependent on the nature of aromatic compound.
In the present work, LaNi0.5Ti0.5O3 and La2NiTiO6 nanoparticles were synthesized by the modified Pechini method. LaNi0.5Ti0.5O3 was calcined at 1073 K for 17 h or 100 h, while La2NiTiO6 was calcined ...at 1273 K for 135 h. The double perovskite calcined at 1073 K for 17 h presented orthorhombic symmetry with Pbnm space group, mean particle size was 31.9 ± 1 nm, random ordering of Ni2+ and Ti4+ cations, Néel temperature close to 15 K, and magnetic moment of 1.29 μB. By increasing the calcination time, this material showed the same symmetry and space group, a mean particle size of 50.7 ± 2 nm, short-range ordering of Ni2+ and Ti4+ cations, Néel temperature around 12 K, and magnetic moment of 0.96 μB. La2NiTiO6 presented a monoclinic crystal structure, with P21/n space group, mean particle size of 80.0 ± 5 nm, rock salt ordering of Ni2+ and Ti4+, Néel temperature of approximately 23 K, and magnetic moment of 2.75 μB.
Cobalt catalysts were prepared by wet impregnation of four distinct supports: alumina, magnesia and two mixed supports of alumina with magnesia (10 and 30 wt%), prepared by wet impregnation of ...magnesia precursor on alumina. Magnesia addition decreased catalyst acidity and reduced spinel phase formation; however, high magnesia content (30 wt%) decreased catalyst reducibility and cobalt dispersion. The catalysts were evaluated on steam reforming of glycerol for 30 h at 500 °C, GHSV of 200,000 h
−1
and a glycerol solution 20% v/v in the feed. All catalysts, except the catalyst supported on pure magnesia, presented deactivation during reaction time, because of coke formation and reoxidation of metallic cobalt phase, mainly for the catalyst supported on 30%MgO–Al
2
O
3
. The catalyst supported on Al
2
O
3
exhibited the highest mean conversion to gas (42.4%) and hydrogen yield (31.2%) during time on stream. However, the catalyst supported on 10%MgO–Al
2
O
3
presented higher stability in terms of glycerol conversion to gas and hydrogen yield, associated with preferential formation of filamentous coke instead of amorphous coke.
Graphic Abstract
La
2
NiTiO
6
double perovskite was synthesized by modified Pechini method. The catalyst activity for steam reforming of methane was investigated at temperatures from 450 to 950 °C, under different ...reduction conditions. By reducing La
2
NiTiO
6
with 10 % H
2
/N
2
at 1,000 °C, the crystalline phase changed to mainly Ni
0
and La
2
TiO
5
, which decreases the onset temperature of methane conversion to 550 °C and provides a maximum methane conversion of 95 % at 950 °C. This activity is higher when compared to that achieved with La
2
NiTiO
6
reduced with 1.8 % H
2
/Ar, which is composed of Ni
0
supported on both non-stoichiometric La
2
NiTiO
6
and La
2
O
3
, and also to those of unreduced La
2
NiTiO
6
and Ni/La
2
O
3
formed by reduction of LaNiO
3
. Activity improvement is related to the increased number of active sites and/or metal-support interaction.
Graphical Abstract
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•Fructose dehydration to HMF was evaluated using phosphotungstic acid (HPW) in DMSO.•92% of HMF yield was achieved with HPW after 30min of reaction at 120°C.•Cs-exchanged HPW resulted ...in a reduction in HMF yield.•80% of HMF yield was reached in 60min, at 120°C, using HPW supported on MCM-41.
The dehydration of fructose to 5-hydroxymethylfurfural (HMF) is a way to produce a very versatile intermediate of the green chemistry. Heteropolyacid compounds are acid catalysts with singular properties (strong acidity and well-defined structure). This paper aims to analyze the activity of phosphotungstic acid (HPW) and Cs-exchanged phosphotungstic acid (HCsPW) in HMF synthesis, as well as HPW supported on MCM-41. The reactions were conducted in a batch reactor, using dimethyl sulfoxide (DMSO) as solvent, for 2h. The initial tests indicated that HMF is formed in the absence of catalyst, but in presence of the catalysts, the maximum yield to HMF is higher and achieved in less time. The HPW showed promising results, reaching 100% of fructose conversion and 92% of HMF yield, after 30min of reaction at 120°C, with a catalyst:fructose mass ratio of 1:10. However, this heteropolyacid is soluble in DMSO. Besides, the Cs-exchanged HPW resulted in a reduction in HMF yield, because of the reduction in solid acidity. HPW supported in MCM-41 (HPW/MCM) showed to be a good solid acid catalyst for the production of HMF from fructose; moreover, it can be recovered and reused. The variables evaluated for this catalyst were the reaction temperature (100, 120 and 140°C) and the catalyst:fructose mass ratio (1:10; 1:30 and 1:50). The best results obtained for HPW/MCM were 100% of fructose conversion and 80% of HMF yield in 60min, at 120°C.
Fluoride can cause some diseases to humans when ingested in large quantities and for a long time. Due to this, it is necessary to remove or reduce the amount of fluoride in effluents before release ...into the water bodies. This work aimed to evaluate the ability of hydrocalumites synthesized by two different methodologies and calcined hydrocalumite in reducing the content of fluoride in aqueous solutions. The materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N
2
physisorption, thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The removal capacity of fluoride ions ranged from 14.9 to 189.6 mg F
−
g
−1
. The removal mechanisms by hydrocalumites were ion exchange and adsorption at low concentrations, while at high concentrations were adsorption and precipitation of calcium fluoride. In relation to the use of calcined hydrocalumite, the removal mechanisms were ion exchange and reconstruction of structure (memory effect) in low concentrations. By the adsorption tests, it was observed that the results fit better the Langmuir isotherm model.
The addition of niobia to nickel/alumina catalysts was evaluated for methane steam reforming, correlating with structural, textural and acid/base properties. The catalysts containing 5–10 wt% Nb
2
O
...5
presented higher methane conversion at 800 °C and did not deactivate during 24 h on stream, while coke formation was inhibited on the catalyst with 20 wt% Nb
2
O
5
.
Graphical Abstract
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•Ni/MgO-Al2O3 catalysts prepared by wet impregnation, coprecipitation, and citrate.•Impregnated catalyst exhibited the highest Ni dispersion and basicity.•High stability during 100 h ...of biogas reforming (CO2/CH4 = 1) at 700 °C.•For Ni/Al2O3 catalyst, the reactor was completely blocked after 30 h on stream.•Coke was mainly graphitic/filamentous for all catalysts.
Hydrogen has been pointed out as a highly potential energy source for the future due to its flexibility in production and utilization. In order to obtain hydrogen sustainably, technologies that use renewable raw materials must be developed. In this context, this work proposes hydrogen production from biogas reforming. Ni/MgO-Al2O3 catalysts, containing 20 wt% of NiO and 10 wt% of MgO, were prepared by three methodologies (wet impregnation, coprecipitation, and citrate) and compared with Ni/Al2O3. The catalyst prepared by impregnation exhibited the highest Ni dispersion and basicity, with the highest activity in methane reforming with CO2 (CO2/CH4 = 1) at temperatures between 600 and 800 °C. This catalyst presented high stability during 100 h of reaction at 700 °C (92 % of CH4 conversion and 95 % of CO2 conversion), with a lower coking rate than Ni/Al2O3. Coke was predominantly graphitic for all catalysts, but the catalyst prepared by coprecipitation showed a higher proportion of amorphous coke and the lowest coking rate.
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