Basicities of alumina-supported alkaline earth metal oxides

Abstract

A series of alumina-supported alkaline earth metal oxide catalysts were prepared by recipient-wetness impregnation. These catalysts were characterized by nitrogen-sorption to determine their surface areas and pore size distributions. The basicities of these catalysts were characterized by temperature-programmed des0rption of carbon dioxide. The TPD results demonstrate that all of the catalysts have one-peak profiles. The basicity increases with increasing atomic number of the alkaline earth metal. The alumina-supported alkaline earth oxides exhibit the same basic properties as bulk metal oxides. However, the presence of alumina can increase the mechanical strength of the catalyst, since the alkaline earth oxides have a weak mechanical strength. The basic properties of the catalysts are strongly influenced by the calcination temperature.

Significance of the structural properties of CaO catalyst in the production of biodiesel: An effect on the reduction of greenhouse gases emission

“…Our results on the optimal calcination/activation temperature were different comparing to the results of some authors [15][16][17][18][19]22]; the reason may be in a fact that precursors of the CaO-based catalysts were various comparing to the compound used in this experiment. Moreover, in our case, the calcination temperatures below 900 °C were not enough high to cause formation of active crystal phase and activation of surface basic sites, while temperatures over 900 °C may induce undesirable sintering of the catalytic material, hence, changes in surface morphology and particle sizes.…”

“…The increase of the calcination temperature to a certain value caused the increase of the CaO activity; the optimal CaO calcination temperature of 550 °C was recognized. This result was explained by dehydration of Ca(OH) 2 and the transformation of CaCO 3 to CaO [16][17][18], and additionally by the amount of active sites [16][17][18]. The FAME yield of rather more than 90% was achieved by using the CaO catalyst calcined at 550 °C after 120 min of the reaction under the following conditions: catalyst amount, based on the oil weight, %: 1.0; average catalyst particle size, µm: 2.8; reaction temperature: 60 °C; agitation speed, rpm: 900 [17].…”

“…Chen et al [16] have studied the basicity of the alumina-supported alkaline earth metal oxides calcined at 550 °C for 6 h (CaO/Al 2 O 3 was calcined at temperatures in the range: 300-750 °C). The basic properties (i.e., the amount of basic sites) of alkaline earth oxides are influenced by the calcination temperature, while the strength of basic sites is not influenced by the calcination temperature.…”

“…The basic properties (i.e., the amount of basic sites) of alkaline earth oxides are influenced by the calcination temperature, while the strength of basic sites is not influenced by the calcination temperature. The calcination temperature of 550 °C yielded the highest amount of basic sites of CaO [16].…”

Transesterification of sunflower oil on single step sol–gel made Al2O3 supported CaO catalysts: Effect of basic strength and basicity on turnover frequency

“…Biodiesel is commonly produced using a soluble catalyst, such as KOH, in the industry but the major drawback of using soluble catalyst is that it may result in soap formation if oil has high free fatty acid and water (Zhang et al, 2003;Meher et al, 2006). Acid, base, or supported enzyme catalysts were used as heterogeneous catalysts in the transesterification of vegetable oils (Van Gerpen, 2005;Xie and Li, 2006;Chen et al, 1998). For example, Suppes et al (2003) reported metal ion-exchanged zeolites were highly active in the transesterification of soybean oil at 100-150°C temperature range in 4-24 h. Enzymatic catalysts, such as lipases, are environmentally friendly but they are expensive and also decrease of activity was observed when immobilized on a support material (Severac et al, 2011).…”