Preparation Of Organic MMT Supported Ni And Application In Hydrogen From Ethanol Steam Reforming

Hydrogen has been known as a promising energy source, because it has been thought as the cleanest and the least pollution. There are many ways for hydrogen production in which ethanol steam reforming（ESR） for its renewable, low toxicity, readily biodegradable, decrease dependence on fossil fuels, and as well as provide a green development path for the development of renewable energy.ESR catalyst focused on Ni catalysts, because of their excellent C-C and CH bond breaking capacity and low cost advantages by researchers of great concern. But it is prone to coke and deactivation, stability needs to be improved. Carriers also affect catalyst activity and stability, not only to activate reaction material, but also dispersion of the active metal, its intensity of acid can also affect the ESR reaction pathway. Montmorillonite（MMT） is a two-dimensional layered silicate clay, weakly acid, its unique characteristic layered structure, cation exchange, good thermal stability is widely used as a catalyst carriers. In this paper, MMT as a carrier, quaternary ammonium cation as intercalation agent, organic montmorillonite（OMMT） were prepared by cation exchange method. Ni/OMMT catalyst was prepared by equal volume impregnation method in OMMT carriers. The activity and the selectivity of ESR were quantitatively correlated with the structure, reduction behavior, and the synergistic effect between different catalytic functions of the catalyst or MMT. These preparation conditions were controlled and characterized by XRD, N₂ adsorption-desorption analysis, H₂-TPR, XPS and SEM analysis. By optimizing organically modified catalyst, structures, conditions to prepare more pretreatment dispersion and more stable and highly active catalyst. The experiment and main conclusions are summarized as follows:（1） 10%Ni/MMT catalysts were prepared by impregnation method, and investigated effect of different calcination temperature and the reaction temperature on the structure and catalytic properties. In the calcination temperature 400℃-700℃, the surface area of 10Ni/MMT decreased from 14.723 to 7.447m²/g. Calcined 10Ni/MMT at 700 ℃, MMT structure was damaged, part of Ni and Al formed Ni Al₂O₄ structure which was difficult to be reduced. For 10Ni/MMT catalysts, at 500℃, LHSV=12mlg^-1h^-1, H₂O/C₂H₅ OH molar ratio of 3:1, with conditions of calcination temperature increased from 400 ℃ to 500 ℃, C₂H₅ OH conversion increased from 65% to 80%, SH₂ is increased from 52% to 62.1%, for calcination temperature 700 ℃, the conversion was 68%, SH₂⁵5%, C₂H₄ O and C₂H₄ were not detected. 10Ni/MMT-500 catalyst stability tests show that the catalytic reaction within 10 h more stable performance, the conversion was 80%, H₂ selectivity of 60%; the conversion decreased after 10 h, accompanying with byproduct C₂H₄ and C₂H₄ O. C deposition amount was 50%, and C rods on the surface of used catalyst was observed by SEM, it indicates carbon deposition reactions occurs on 10Ni/MMT-500 catalysts and lead to poor activity and deactivation.（2） OMMT was prepared from alkane chain quaternary ammonium and MMT by cation exchange. Effects of different types of quaternary ammonium salts and varying amounts（multiples of cation exchange capacity（CEC）） of cetyltrimethyl ammonium bromide（CTAB） on MMT structure, spacing and arrangement of the interlayer were investigated. When the C atoms of the quaternary ammonium salt increase from 15 to 21, which consists of monolayer tile into paraffin type monolayer arrangement between the layers; CTAB content increased from 0.5CEC to 1.5CEC, OMMT of d001 increase from 1.25 nm to 4.13 nm, d001 reduced to 3.68 nm at 2CEC, interlayer cations are arranged into tile monolayer layer into a paraffin type bilayer.（3） Effects of amount of CTAB, different Ni precursors, the reaction temperature, the amount of metal loading on the ESR was investigated. For the nitrate Ni as source of nickel, 10Ni/0.5-2CTAB-MMT were prepared by 0.5-2CEC of OMMT supported 10wt%Ni by impregnation method, the catalyst surface area of from 95 m²/g to 137.60 m²/g. Over reaction temperature 500℃, H₂O/C₂H₅ OH molar ratio of 3:1, and LHSV=12 mlg^-1h^-1, 10Ni/0.5CTAB-MMT and 10Ni/1CTAB-MMT catalysts, their C₂H₅ OH conversion reached 99%, H₂ selectivity increased from 68.2% to 72.4%; for CTAB content at 2CEC, C₂H₅ OH conversion was 90%, H₂ selectivity was 59%, the activity decreased. Ni loading were 7, 10, 15wt%, C₂H₅ OH conversion ¹00%; 3wt% and 5wt%Ni/OMMT, C₂H₅ OH conversion ⁵8.7%, 78%, respectively, indicating that Ni loading is the greater, the activity of the catalyst is higher. At reaction temperature of 500℃, H2O/C₂H₅OH=3:1, LHSV=12mlg^-1h^-1, Ni loading of 10%, ethanol conversion was 100%, H₂, CO, CO₂, CH₄ selectivity was 72.4%, 5.3%, 20.1%, 3.8%, and accompaning with C₂H₄ C₂H₄ O, and 10%Ni/OMMT catalyst carbon deposition during 30 h is 20%, but obvious deactivation was no observed. Carbon deposition occurs only on the outer surface of the catalyst, which has little effect on the active center of the catalyst layer. When the Ni source is nickel sulfate, with the increase of calcination temperature from 550℃ to 900℃, catalyst specific surface area decrease from 87 m²/g to 10.6 m²/g, pore volume from 0.14 cm³/g down to 0.02 cm³/g. For Ni（NH₂SO₃）₂/OMMT calcination temperature < 800 ℃, the main generating Ni SO₄, C₂H₅ OH conversion was 30.7%, H₂ selectivity was 38.3%; at the calcination temperature>800℃, high-temperature calcination to generate Ni O, C₂H₅ OH conversion increased to 92.6%, H₂ selection to 72%, so calcined nickel sulfamate at low temperature poor response to the ESR active. Catalytic properties of nickel nitrate precursor is superior to nickel sulfate. The modification of MMT with CTAB can significantly improve the stability of the Ni/OMMT catalyst in ethanol steam reforming and reduce the carbon deposition rate by immobilizing highly dispersed nanoparticle Ni on the interlayers of OMMT, the selectivity to ethylene and acetaldehyde is also greatly depressed.