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Effect of hydrothermal treatment on properties of Ni–Al layered double hydroxides and related mixed oxides

“…In general, two essential stages can be observed during phase transformation of LDHs upon heating: (i) a shift of LDH basal spacing associated with release of interlayer water and (ii) disappearing of the LDH diffraction lines and formation of oxide phases. Stanimirova et al [10] discussed the mechanism of LDH collapse; the collapsed phase retaining the layered structure of the pristine LDH was denoted as metahydrotalcite B. An analogous phase observed during heating of cobalt-containing LDHs we denoted as collapsed LDH; it had basal spacing decreased typically from about 7.6 to 6.6 Å [28].…”

“…Thermal decomposition of LDHs was studied by many authors, a great number of studies were performed namely with synthetic Mg-Al hydrotalcite [7][8][9]. Two characteristic processes accompanied by a considerable weight loss and an endothermic effect can be observed during hydrotalcite heating: The release of interlayer water at 150-200 1C accompanied by a collapse of the LDH basal spacing [9,10] and the complete decomposition of the layered structure at 350-600 1C. The resulting structurally disordered oxide mixture crystallizes to form MgO-like phase above 400 1C; MgO and MgAl 2 O 4 spinel are detected above 900 1C.…”

Synthesis and characterisation of hydrotalcites produced by an aluminium hazardous waste: A comparison between the use of ammonia and the use of triethanolamine

“…In this step, ratio 2:1 showed a moderate increase in the temperature required for the removal of the interlayer water in contrast to the other ratios which presented similar behaviours (small endothermic peak in DTA at around 207°C). The second region in TG (from 215 to 300°C) showed a very slight decrease in mass which was higher for lower ratios and could be associated with the beginning of the removal of the OH − bonded to Al 3+ (Stanimirova et al, 1999;Yang et al, 2002;Vágvölgyi et al, 2008). DTA signals indicated a more stable stage for materials co-precipitated with ammonia.…”

Síntese, caracterização e estudo de propriedades catalíticas de hidróxidos mistos lamelares contendo Cu(II)/Mg(II)/AI(III)

“…Tal hipótese foi confirmada por Starminova et al [94] , e mais recentemente por Kanan et al [95] , elucidando o processo de decomposição térmica ao mesmo tempo que propõe uma estrutura para o material obtido em cada uma das etapas. Por outro lado, Kloprogge et al [96] , atribui tal abaixamento de simetria nos íons carbonato apenas à presença de um segundo tipo de íon carbonato livre (não coordenado ou enxertado) que teve sua simetria alterada devido à interações mais fortes com sua vizinhança.…”

“…→ Cu(II) [87], [98] . Essa proposta corrobora com os estudos de Stanimirova et al [94] produto da oxidação da hidroquinona. Na Figura 37 está representada a estrutura do fenol e dos três produtos obtidos para a reação.…”