Transition Metal B-Site Substitutions in LaAlO3 Perovskites Reorient Bio-Ethanol Conversion Reactions

Abstract

LaAlO3 perovskites, as such and with 25% molar Al substitution by Cu, Co, or Ga, have been prepared by sol-gel methods and tested as heterogeneous catalysts in the gas-phase conversion of ethanol. LaAlO3 presented a significant acidic character, with high formation of ethylene by ethanol dehydration. B-site substitutions increased the basicity of the catalysts, favoring the dehydrogenation of ethanol to acetaldehyde. The most reducible Cu- and Co-substituted materials, characterized by easier formation of surface oxygen vacancies, promoted the self-condensation of acetaldehyde by the Tishchenko mechanism, with formation of acetone and odd-carbon number products. Aldol coupling of acetaldehyde, favored on pure and Ga-substituted LaAlO3, led to the formation of butadiene and hexadiene. The role of Ga insertion, favoring both dehydrogenation of ethylene and dehydration of higher alcohols, corresponds to an amphoteric character. The formation of olefins and diolefins on all catalysts suggests that LaAl-based materials present the most acidic character among La-perovskites.

Green and Efficient Al-Doped LaFexAl1–xO3 Perovskite Oxide for Enhanced Phosphate Adsorption with Creation of Oxygen Vacancies

“…It was observed that the cell parameters of LFAO-3 decreased, i.e., the smaller radius of Al 3+ ( r Al = 0.39) took the place of the larger radius of Fe 3+ ( r Fe = 0.55), which may result in a decrease in the sample particle size . The lattice parameters of V-LFAO-3 were further reduced, and the crystal distortion rate further increased, indicating that oxygen defects affect crystal growth during sintering …”

“…38 The lattice parameters of V-LFAO-3 were further reduced, and the crystal distortion rate further increased, indicating that oxygen defects affect crystal growth during sintering. 41 The sample exhibits slight absorption peaks at ∼3440, 1630 cm −1 , and 1460 cm −1 which are attributed to the stretching of −OH groups of water, the bending vibration of H−O−H, and the stretching vibration of C−O, respectively (Figure 1c). 42 The vibration bands of 535 and 418 cm −1 (Figure 1d) belonged to the tensile vibration of Fe−O and the stretching vibration of O−Fe−O, respectively.…”

La-Doped Alumina, Lanthanum Aluminate, Lanthanum Hexaaluminate, and Related Compounds: A Review Covering Synthesis, Structure, and Practical Importance

“…The application in thermal barrier coatings was also considered, whereby layered perovskites of so-called Ruddlesden–Popper structure have an exceptional low thermal conductivity . Chemical, − combustion-, ,− environmental, , , − photo-, , and electrocatalysis − are other areas of potential use. , , − Electrocatalysis includes high-temperature solid-oxide electrolysis cells and water splitting. − Photocatalysis includes water splitting ,− and CO 2 conversions . Emery et al performed a computational screening of perovskites for the solar-driven thermochemical splitting of water, resulting in 139 promising candidates.…”

A New Approach to Fuel Cell Electrodes: Lanthanum Aluminate Yielding Fine Pt Nanoparticle Exsolution for Oxygen Reduction Reaction

“…[11] Among various perovskite oxides, LaAlO 3 exhibits high chemical resistance, high thermal stability, high transparency, high dielectric constant, low toxicity, and good catalytic activity. [12,13] Owing to its surface acidic properties, LaAlO 3 has been investigated for various applications, i.e., Imai and Tagawa et al used it for the oxidative coupling of methane, [14] Wang et al for the degradation of pollutants, [15] Tran et al for hydrogenation and dehydrogenation of hydrocarbons [13] and CO 2 methanation, [13] Mukai et al for steam reforming, [16] Deng et al for far-infrared radiation applications, [17] Shaik et al for drug delivery, [18] and Sato et al for oxidative coupling of methane. [19] Published studies have reported that A-and B-site substitution of LaAlO 3 with various noble and transition metal ions, e.g., A-site with Sr, Ca, Nd, [20][21][22] and B-site with Rh, Ni, Co, Cu, Ga, Cr, Ce, Mn, Pt, Ru, Pd, changes the electrical, catalytic, optical, and magnetic properties by modifying oxygen vacancy concentration, and valance states of elements.…”

“…[19] Published studies have reported that A-and B-site substitution of LaAlO 3 with various noble and transition metal ions, e.g., A-site with Sr, Ca, Nd, [20][21][22] and B-site with Rh, Ni, Co, Cu, Ga, Cr, Ce, Mn, Pt, Ru, Pd, changes the electrical, catalytic, optical, and magnetic properties by modifying oxygen vacancy concentration, and valance states of elements. [13,17,[23][24][25] Hashimoto et al reported that the A-site substitution of LaAlO 3 , Sr substitution in La-sites, improved oxygen ionic mobility by inducing the formation of oxygen vacancies; on the other hand, A-site deficiency worsened the oxygen ionic conductivity, perovskite oxide behaved like an ionic insulator. [26] For B-site doping, Anil et al observed improved catalytic activity for the B-site Ru, Pt and Pd (2%) substituted LaAlO 3 .…”