470
interesting study, Kim et al. [82] prepared various H-zeolites which include
H-ferrierite, H-Y, H-β, HZSM-5 and H-mordenite with different Si and Al ratios.
Among these H-ferrierite showed highest selectivity for acrolein of 77% at favourable conditions. For this catalyst the selectivity of acrolein has a monotonal increase
with increase in reaction temperatures. On the other side, the conversion of glycerol
is seen to increase while having longer contact time, but acrolein selectivity is found
to decrease gradually. In an interesting study by Possato et al. [83], they have tried
to escalate the conversion of glycerol by applying the desilication methodology
where they have tried to minimize diffusion limitations by secondary pore formation in zeolite catalysts. They observed increase in conversion of glycerol due to the
weakened surface acidity and an increase in accessibility of the active sites by glycerol. Longer catalyst stability and very few blocked micropores are the main convenience in this method. Qureshi et al. [71] synthesized nano-H-ZSM-5 catalyst with
short channels. The Si and Al ratio is varied, and the catalyst with Si/Al = 75 showed
the best results at 81% glycerol conversion with 86% of acrolein selectivity at 10 h
time on stream at 320 °C temperature. Ding et al. [72] developed microstructured
ZSM-11 catalyst by direct growth on sinter-locked stainless steel microfibres. It
exhibited very good reactivity and stability over other reported zeolites. It reached
up to a glycerol conversion of 95% with 60% selectivity towards acrolein. The formation of coke was suppressed due to enhanced diffusion through zeolite pores at
high flow of carrier gas. Also a new nanosheet MFI zeolite with different Si/Al
molar ratio was prepared, and it could achieve a glycerol conversion of 99% with
86.6% acrolein selectivity for 12 h TOS [73].
Various types of mixed oxides, metal pyrophosphates and phosphates are also
extensively used in glycerol dehydration into acrolein. Chai et al. [84] used Nb 2 O 5
catalyst for glycerol dehydration reaction at 315 °C where effect of different calcination temperatures, acidity, catalyst structure and crystal structure was studied.
Glycerol conversion of 88% with 51 mol.% selectivity for acrolein was observed.
Suprun et al. [56] explored gas phase glycerol dehydration over aluminium phosphate (AlPO 4 ), titanium phosphate (TiPO 4 ) and silica-alumina phosphates (e.g.
SAPO-11 and SAPO-34). The glycerol conversion was found to be dependent on
the acidity and textural characteristics of the catalyst. The catalyst SAPO-34 could
achieve 59% conversion of glycerol with 72% acrolein selectivity, but its drawback
was fast deactivation. Wang et al. [85] probed different types of vanadium phosphate catalysts where various reaction parameters could be varied to ultimately
achieve 66% acrolein selectivity at complete conversion of glycerol. The oxygen
flow in the reaction ended up giving good results. In another study on vanadium
pyrophosphate oxides, Wang et al. did some temperature study on the catalysts and
found out that morphology, crystallinity and acidity changed with it. The catalyst
treated at temperature 1073 K exhibited 64% selectivity for acrolein at 100% glycerol conversion. Deleplanque et al. [55] synthesized iron phosphates in hydrothermal methods which could obtain an acrolein yield of 92%, and the catalyst showed
activity up to 25 h. Dubois [86] performed glycerol dehydration on potassium (K)-,
strontium (Sr)- and caesium (Cs)-doped phosphate catalyst, where Cs-catalyst
obtained 72% acrolein yield. In a different study by Lauriol-Garbey et al. [43], they
K. Bhaduri et al.
interesting study, Kim et al. [82] prepared various H-zeolites which include
H-ferrierite, H-Y, H-β, HZSM-5 and H-mordenite with different Si and Al ratios.
Among these H-ferrierite showed highest selectivity for acrolein of 77% at favourable conditions. For this catalyst the selectivity of acrolein has a monotonal increase
with increase in reaction temperatures. On the other side, the conversion of glycerol
is seen to increase while having longer contact time, but acrolein selectivity is found
to decrease gradually. In an interesting study by Possato et al. [83], they have tried
to escalate the conversion of glycerol by applying the desilication methodology
where they have tried to minimize diffusion limitations by secondary pore formation in zeolite catalysts. They observed increase in conversion of glycerol due to the
weakened surface acidity and an increase in accessibility of the active sites by glycerol. Longer catalyst stability and very few blocked micropores are the main convenience in this method. Qureshi et al. [71] synthesized nano-H-ZSM-5 catalyst with
short channels. The Si and Al ratio is varied, and the catalyst with Si/Al = 75 showed
the best results at 81% glycerol conversion with 86% of acrolein selectivity at 10 h
time on stream at 320 °C temperature. Ding et al. [72] developed microstructured
ZSM-11 catalyst by direct growth on sinter-locked stainless steel microfibres. It
exhibited very good reactivity and stability over other reported zeolites. It reached
up to a glycerol conversion of 95% with 60% selectivity towards acrolein. The formation of coke was suppressed due to enhanced diffusion through zeolite pores at
high flow of carrier gas. Also a new nanosheet MFI zeolite with different Si/Al
molar ratio was prepared, and it could achieve a glycerol conversion of 99% with
86.6% acrolein selectivity for 12 h TOS [73].
Various types of mixed oxides, metal pyrophosphates and phosphates are also
extensively used in glycerol dehydration into acrolein. Chai et al. [84] used Nb 2 O 5
catalyst for glycerol dehydration reaction at 315 °C where effect of different calcination temperatures, acidity, catalyst structure and crystal structure was studied.
Glycerol conversion of 88% with 51 mol.% selectivity for acrolein was observed.
Suprun et al. [56] explored gas phase glycerol dehydration over aluminium phosphate (AlPO 4 ), titanium phosphate (TiPO 4 ) and silica-alumina phosphates (e.g.
SAPO-11 and SAPO-34). The glycerol conversion was found to be dependent on
the acidity and textural characteristics of the catalyst. The catalyst SAPO-34 could
achieve 59% conversion of glycerol with 72% acrolein selectivity, but its drawback
was fast deactivation. Wang et al. [85] probed different types of vanadium phosphate catalysts where various reaction parameters could be varied to ultimately
achieve 66% acrolein selectivity at complete conversion of glycerol. The oxygen
flow in the reaction ended up giving good results. In another study on vanadium
pyrophosphate oxides, Wang et al. did some temperature study on the catalysts and
found out that morphology, crystallinity and acidity changed with it. The catalyst
treated at temperature 1073 K exhibited 64% selectivity for acrolein at 100% glycerol conversion. Deleplanque et al. [55] synthesized iron phosphates in hydrothermal methods which could obtain an acrolein yield of 92%, and the catalyst showed
activity up to 25 h. Dubois [86] performed glycerol dehydration on potassium (K)-,
strontium (Sr)- and caesium (Cs)-doped phosphate catalyst, where Cs-catalyst
obtained 72% acrolein yield. In a different study by Lauriol-Garbey et al. [43], they
K. Bhaduri et al.