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Lithium-ion batteries are essential for portable technology and are now poised to disrupt a century of combustion-based transportation. The electrification revolution could eliminate our reliance o...

Bifunctional catalysts of Cu·ZnO supported on modified γ-Al2O3 were prepared and tested in the direct hydrogenation of CO2 to methanol and dimethyl ether (DME). The γ-Al2O3 modification was carried...

Vapor phase hydrodeoxygenation (HDO) is a prospective route for upgrading the downstream products derived from fast pyrolysis of lignocellulosic biomass. The objective is to produce transportation fuel or value-added chemicals using a sustainable feedstock. This work reports a thermodynamic chemical equilibrium analysis of the vapor phase HDO of guaiacol (2-methoxyphenol), model compound representative of the lignin portion of biomass,. The chemical equilibrium was determined by simulation in the temperature range of 500–1000 K, 1 atm, and using an isothermal equilibrium reactor. These conditions were chosen to match the atmospheric HDO of guaiacol studies. The equilibrium constant and the equilibrium conversion values determined may help on the explanation of reaction pathways of the catalytic HDO of guaiacol. Most of the reactions behaved exothermically and did not show thermodynamic restriction to occur, except the hydrogenation of the aromatic ring. The desirable reactions which remove oxygen without breaking C–C bonds were thermodynamically favored. The most stable molecules were dependent on both temperature and guaiacol concentration at feed.

The aim of this work was to investigate the effect of the calcination temperature on the textural properties, structure and acidity of niobium phosphate and the relationship between those properties and the catalytic activity for the continuous esterification reaction using oleic acid and ethanol. For this purpose, samples of niobium phosphate were prepared by calcination at 300, 350, 400, 450, 500 and 600 °C. Despite the good thermal stability presented by niobium phosphate, best results were achieved for samples pretreated at 300 °C, which presented higher acidity, surface area and catalytic activity. For this sample, the experimental conditions of temperature (from 220 to 290 °C), amount of catalyst (from 0 to 0.8 g) and ethanol:oleic acid molar ratio (from 2:1 to 14:1) were studied using design of experiments (DOE) and optimized with canonical analysis. The esterification reaction of oleic acid led to yields of esters up to 70% and conversion up to 90% at optimized conditions.

5-Hydroxymethylfurfural (HMF) production from fructose was studied by using niobium phosphate as solid acid catalyst. HMF selectivity was optimized in a water-acetone system and compared to a water system. The HMF optimal selectivity for process carried out in the water-acetone system was 62.94%. When the process was performed in water, the HMF selectivity achieved 55.73%. These results were used in a large-scale simulation and economic analysis of the two processes. The higher selectivity of system water-acetone affected the HMF minimum selling price (MSP). The MSP value was 2.21 USD/kg for process performed in water-acetone and 3.05 USD/kg for process in water. In the sensitivity analysis, we have found that in addition to process selectivity, the fructose cost was the most significant factor affecting HMF price.

The objective of this work was to observe the significant factors for the dehydration reaction of xylose to furfural and to optimize the processes using experimental design. The studied variables were temperature, time, initial percentage of xylose mass, and catalyst/xylose ratio. Temperature and initial percentage of xylose mass were considered statistically significant, while the maximum point for furfural selectivity was at 160 °C and 2% of initial xylose mass. Using niobic acid and niobium phosphate (1:1) (NbP/NbA), 44.05% xylose conversion and 74.71% furfural selectivity were obtained. The results showed that the mixture of catalysts with Bronsted acid and Lewis acid sites improved the selectivity of furfural from the xylose dehydration reaction. NbP/NbA catalysts were very stable under the investigated condition after 5 continuous recycles.

The aim of this work was to evaluate the continuous production of biodiesel through the esterification reaction between oleic acid and ethanol using niobic acid as a solid acid catalyst. In this study, different calcination temperatures of niobic acid were tested. W/F tests were carried out, to avoid mass transfer problems and, then, the catalytic activities of all the samples were evaluated. Results showed that niobic acid calcined at 350 °C presented the highest catalytic activity. The experimental conditions of temperature, amount of catalyst and ethanol:oleic acid molar ratio were optimized by using design of experiments (DOE) and canonical analysis. All three single parameters were significant on the yield of esters. The esterification reaction of oleic acid led to yields of esters up to 70% and conversion up to 90%, at 249 °C, ethanol:oleic acid molar ratio of 10.83:1 and 0.7 g of niobic acid.

The aim of this work was to optimize the acid-catalyzed conversion of glucose into 5-hydroxymethylfurfural (HMF) in an aqueous medium using niobic acid (NbO), niobium phosphate (NbP) and a mixture of both solid acid catalysts. A simplex-centroid mixture design was applied to optimize the mixture ratio between NbO and NbP. A central composite design was applied to process optimization. The studied variables were temperature (T), time (t) and substrate to catalyst weight ratio (R S/C ). The mixture design revealed excellent glucose conversion (55%) and HMF selectivity (56%) when the weight ratio between NbO and NbP was equal to 1:1. The experimental results demonstrate that a mixture of both solid acids provides a better combination of Bronsted and Lewis acidity for effective glucose dehydration into HMF than each individual catalyst.

Pt/xNb2O5/(100-x)Al2O3 (x = 0, 5, 20, 100, wt.%) catalysts were tested on the gas phase hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol, C7H8O2), model compound representative of the lignin-derived portion of the bio-oil produced after pyrolysis or HTL. The physicochemical properties of the catalysts were analyzed by XRD, N2 physisorption, CO chemisorption, and temperature programmed desorption of isopropylamine. The catalytic performances were evaluated in a continuous flow system at atmospheric pressure with the aim of reducing the oxygen content of the guaiacol molecule as an upgrading step of the biomass processing. The influence of H2 partial pressure, temperature, space velocity, and pure supports performance on both activity and selectivity was determined. The Pt/Nb2O5 catalyst exhibited superior oxygen removal. Niobia addition enhanced the selectivity towards phenol while Pt/Al2O3 formed mainly catechol. The interaction between Pt and NbOx species probably enables oxophilic sites formation which enhances DDO reaction towards phenol formation and less deactivation even at low hydrogen content.

Nickel-rich layered LiNi0.8Co0.1Mn0.1O2 is a promising cathode material due to its high specific capacity. However, commercial application of this material is impeded by its rapid capacity degradation associated with structural instability. In this work, 0.5–2 mol% Nb5+ doped LiNi0.8Co0.1Mn0.1O2 cathode material is prepared by heat treatment of a mixture of stoichiometric amounts of nano-sized Nb2O5 powders, co-precipitated NixMn1-x(OH)2 precursors, and LiOH·H2O. The results show that Nb5+ doping significantly improves the cycling properties of LiNi0.8Co0.1Mn0.1O2 cathode material and that the optimal Nb5+ content in the structure is 1 mol%. Under a voltage range of 2.75–4.3 V, 1 mol% Nb5+ doped LiNi0.8Co0.1Mn0.1O2 cathode material shows an initial discharge capacity of 180.2 mAh/g at 0.1C, with a capacity retention of 96.9% for subsequent 300 cycles at 1C at room temperature. In contrast, bare LiNi0.8Co0.1Mn0.1O2 shows a capacity retention of only ~79.8% under the same conditions, with an initial specific discharge capacity of 184.9 mAh/g. The improvement in cycling performance is attributed to stabilization of the layered structure by Nb5+, mitigated migration of Ni2+ to the Li layer, improved lithium diffusion kinetics and reduced lattice expansion/shrinkage during cycling. Stabilization of the layered structure by Nb5+ doping is further reflected by the observation of fewer cracks in cathode electrodes after prolonged cycling.

This paper reports the synthesis of a new class of catalysts based on niobium using Filter Cake (FC) as precursor, which is more affordable economically than other niobium sources commonly used. FC is obtained before the necessary purification to obtain niobic acid (Nb2O5∙nH2O), making the catalyst synthesis process less costly. Its modification by hydrothermal treatment in the presence of different agents (oxalic acid or hydrogen peroxide) allowed the obtention of nanostructured materials in the form of rods or spheres with larger BET area, crystallinity and acidity than the precursor. Their catalytic potential were evaluated in fructose dehydration reaction in aqueous media, aiming the obtention of 5-hydroxymethylfurfural (5-HMF). The production of furan compounds from sugars has become a process of great interest in recent years because it is related to the search for more sustainable sources of energy, since carbohydrates are the predominant part of biomass. In optimum conditions, it was possible to obtain 22% yield of 5-HMF in aqueous medium and 47% yield of 5-HMF using DMSO as solvent.

We report the synthesis, characterization and catalytic evaluation of Cu·ZnO catalysts supported on Al 2 O 3 and Nb 2 O 5 , as acidic materials, to study the CO 2 hydrogenation to methanol and dimethyl ether. The catalysts were prepared by precipitation or impregnation of the metals over the supports. They were characterized by different techniques, such as XRF, BET area, TPD of n -butylamine, XRD and TPR. Catalytic tests were performed in an automated catalytic unit coupled to a gas chromatograph with FID and TCD detectors. Different conditions of temperature and pressure were studied. It could be observed that the choice of the synthesis method affects the activity and selectivity of the CO 2 hydrogenation, at the conditions used in this work. The catalyst prepared by impregnation of the metals over the Al 2 O 3 support was the most active and selective to dimethyl ether. This result can be explained by the better and lower temperature reducibility of CuO particles along with higher density of acid sites and strength of the alumina support.

This study investigated the production of furfural from sugarcane bagasse over niobic acid (Nb2O2·nH2O, called as NbO) or niobium phosphate (NbOPO4·nH2O, called as NbP) in a one-step process performed in water. The variables temperature (T), the mass of catalyst (mcat), reaction time (rt), and vibration time (Vt) for mixing SCB and catalyst were studied through a design of experiments. After 5 h at 150 °C, the furfural yields were 52.1 g kg−1 for NbO and 59.3 g kg−1 for NbP, while the yields of xylose and arabinose were, respectively, 69.7 g kg−1 and 6.4 g kg−1 for NbO and 147.4 g kg−1 and 11.1 g kg−1 when using NbP. It was proved that furfural yield is independent of the SCB genotype. The selective depolymerization and hydrolysis of hemicellulose into monomers and its further dehydration to furfural were observed. The cellulose and lignin remained readily utilizable for further processing. The better catalytic performance of NbP was attributed to the higher ratio of Bronsted to Lewis acid sites on its surface than NbO.

An increase in the PdO surface area by a factor of about 20 was observed after treatment of Pd foils in excess methane at 598 K. The surface area was increased as the O2 partial pressure in the activation treatment was decreased. The activated foil was probed by the reaction of complete oxidation of methane in excess O2. The rate was proportional to the PdO surface area and thus the turnover rate per unit of PdO area was the same as that for the untreated foil. Critical for this assessment was the determination of the PdO surface area measured by exchange of surface oxygen with 18O2. The PdO surface area decreased after interaction with water when the sample was cooled. After treatment of the foil in excess methane, PdO but not Pd was identified by X-ray photoelectron spectroscopy, and carbon deposits from methane were identified on the surface and in the bulk by temperature-programmed desorption.

The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO 3 /Al 2 O 3 catalyst than on the Pd/CeO 2 /Al 2 O 3 and Pd/Nb 2 O 5 /Al 2 O 3 catalysts. The explanation for the very high N 2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me δ + stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N 2 selectivity.

Pd–chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature.

The influence of the preparation method and loading of CeO 2 on the interaction of Pd/CeO 2 /Al 2 O 3 catalysts was studied. The materials were characterized by temperature-programmed reduction, hydrogen chemisorption and X-ray photoelectron spectroscopy measurements. The 1,3-butadiene hydrogenation was used as a model reaction. The Pd Ce interaction affected the reduction behavior of the catalysts. Temperature-programmed reduction (TPR) results showed that the presence of CeO 2 shifts the reduction temperature of PdO to lower values, while palladium similarly facilitates the reduction of the cerium surface species. The hydrogen uptake decreased when increasing the ceria content. XPS results showed that the Pd/Al ratio decreased with CeO 2 addition being affected by the preparation method and content. The formation of catalytic sites at the interface of Pd Ce was postulated from turnover frequency (TOF) results of the 1,3-butadiene hydrogenation. The number of these new sites increases with the addition of ceria. The nature of these sites is discussed in terms of the influence on the selectivity in butadiene hydrogenation.

Niobic acid, Nb2O5.nH2O (Niobia HY-340), was successfully applied to the industrial production of biodiesel from the esterification of free fatty acids of palm oil at Agropalma plant, located in the city of Belem, State of Para, in the northern part of Brazil. The biodiesel plant has a production capacity of approximately 25,000 metric tons of biodiesel per year and it is the first plant in the world to use a heterogeneous catalyst for biodiesel production. As a solid acid catalyst niobic acid was very effective, presenting superior performance to commercial acid zeolites. The Agropalma plant started its operation in April 2005 and since then they are continuously producing biodiesel, branded as PalmDiesel®, of extremely high quality exceeding by far the strict European EN 14214 regulation.

The role of palladium precursors (e.g. chloride — PdCl2; acetylacetonate — Pd(acac)2; nitrate — Pd(NO3)2) in the catalytic properties of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts toward CO oxidation was herein investigated. The characterization techniques used for mapping the Pd sites were H2 and CO chemisorption, infrared spectroscopy (FTIR) of CO adsorbed, and temperature-programmed desorption (TPD). Unsteady-state CO oxidation was carried out by temperature-programmed surface reaction (TPSR). The nature of palladium precursors and their interaction with CeO2 affected the metallic dispersion and the site morphologies. Highly dispersed metal particles (d>50%) were obtained by using palladium chloride and acetylacetonate precursors on Pd/Al2O3 catalysts. Pd(1 0 0) and Pd(1 1 1) were the major palladium crystallite orientations in these samples, but a larger amount of low coordination sites located on Pd(1 0 0) faces was observed for the ex-chloride sample. These sites accounted for the oxidation of CO at very low temperatures on Pd-Cl catalyst. In the presence of ceria, the Pd dispersion was a function of the way in which each Pd precursors interacted with CeO2. A two-fold decrease of dispersion was obtained to ex-chloride sample, while a two-fold increase to ex-nitrate and the same dispersion to ex-acetylacetonate samples were otherwise observed. The metallic redispersion may be the result of the occupancy of ceria oxygen vacancies by the palladium crystallites. Ultimately, the interaction with ceria redispersed Pd crystallites in a more organized bi-dimensional structure with the predominance of (1 1 1) orientation. Due to the transient conditions of the reaction, ceria did not promote, as expected, the oxidation of CO. Ceria reduced species (Ce3+) were not able to help CO oxidize at lower temperatures due to lack of oxygen into its lattice. Thus, the highest rates for CO oxidation were only observed at higher temperatures for the Pd/CeO2/Al2O3 catalysts, a result of a combination of strong competition for oxygen molecules, which have replenished the ceria lattice, and the low activity of Pd(1 1 1) sites.