LDH derived MgAl2O4 spinel supported Pd catalyst for the low-temperature methane combustion: Roles of interaction between spinel and PdO

Insights on Guerbet Reaction: Production of Biobutanol From Bioethanol Over a Mg–Al Spinel Catalyst

“…The catalyst exhibits low–moderate basic sites at lower temperatures mainly, although it is possible to distinguish weak desorption at 618°C, indicating strong basic sites formation. Song et al (2021 ) ascribe these peaks to the formation of the different carbonate geometries because of reactive CO 2 absorption. The peak at 180°C could be related to the bicarbonate anions associated with the presence of hydroxyl groups; meanwhile, the peak at 371°C is ascribed to bidentate carbonates on acid–base sites (Al 3+ –O 2− or Mg 2+ –O 2− ) ( Díez et al, 2003 ).…”

“…We differentiate two zones associated with the acid strength, depending on the NH 3 temperatures desorption: moderate (200–400°C) and strong (400–800°C) ( Madduluri et al, 2020 ). The peak at a lower temperature, 256°C, is associated with reversible adsorption H-bonded ascribed to hydroxyl groups presence over the surface, considered as BrØnsted acid sites ( Song et al, 2021 ). Alternatively, the peaks at high temperatures (450–510°C) are related to Lewis acid sites, showcasing the interaction with accessible Al +3 cations in Al 3+ –O 2− –Mg 2+ , because of possible defects present over the spinel surface ( He et al, 2015 ).…”

Advancement of modification engineering in lean methane combustion catalysts based on defect chemistry

“…In heterogeneous catalysis, the Strong Metals-Support Interaction (SMSI) can significantly enhance the adsorption of CH 4 and the activity of lattice oxygen of the supports, [104][105][106] and strongly modify the dispersion and morphology of the metal particles. [107][108][109] For example, Wu et al 110 prepared a highly dispersed palladium catalyst supported on defective Al 2 O 3 -CeO 2 (RAl 2 O 3 -CeO 2 : ceria was immobilized on the coordinatively unsaturated Al 3+ penta sites of γ-alumina activated by pre-reduction to fabricate hybrid-oxide support) for methane combustion. The RAl 2 O 3 -CeO 2 interface as such can be effective in enhancing the catalytic activity because such an interface increases the dispersion of the deposited Pd species.…”

Synthesis and Thermal Degradation of MAl4(OH)12SO4·3H2O with M = Co2+, Ni2+, Cu2+, and Zn2+

“…LDH materials are known for their versatile chemistry of both cation and anion layers, as well as their anion exchange properties . Thus, they have potential applications as materials for catalysts, , drug carriers, environmental remediation, − and energy materials. , Interestingly, hydrotalcite LDHs are used as precursors in the preparation of catalytic mixed metal oxide (MMO) composite materials, where the LDHs are calcinated at high temperatures. ,, Here, the LDH intermediate serves a dual purpose, where the flexible LDH chemistry allows for both fine-tuning of the metal ratios in the final MMO and ensures a homogeneous mixture of the starting materials, which is otherwise difficult to obtain using direct synthesis methods. ,, Moreover, MMO made from calcinated LDH is often porous, with larger surface areas, than MMO made by conventional routes, and therefore poised for applications as adsorbents or catalysts. ,,,, …”

“…Many studies have investigated the thermal degradation of hydrotalcite-type LDH, ,− ,− especially MgAl–CO 3 - and ZnAl–CO 3 -LDH with various M/Al ratios. ,,− ,,, Generally, hydrotalcite M 1– x Al x -LDH degradation proceeds by the loss of surface and interlayer water at ca. 200 °C followed by dehydroxylation of the hydroxide layer and removal of interlayer anions between 200 and 500 °C. ,,,, This yields an amorphous phase, ,,,, often embedded with crystalline metal oxide (MO) particles as observed for MgAl–CO 3 - and ZnAl–CO 3 -LDH. ,, Moreover, the amorphous phase contains both tetrahedral and octahedral Al based on solid-state 27 Al nuclear magnetic resonance (NMR) spectroscopy. ,,,, Above 800–1000 °C, a physical mixture of a crystalline spinel (MAl 2 O 4 ) and MO is formed, where the spinel content is controlled by the Al content ( x ) of the hydrotalcite, M 1– x Al x -LDH. ,,,,, …”