Effect of phosphorus precursor on the catalytic performance of metal phosphides in the methanation of syngas
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摘要: 采用氢气程序升温还原方法制备了系列金属磷化物催化剂,研究了磷前驱体和H2/CO比对其甲烷化催化性能的影响。结果表明,与磷酸氢二铵相比,由植酸制备的金属磷化物催化剂具有较高的甲烷化活性;植酸作为螯合剂可以有效地分散金属前驱体,降低还原温度,使催化剂具有较高的比表面积和较小的晶粒尺寸,并更好地还原为纯磷化物晶相。不同金属磷化物催化剂的活性顺序为MoP > WP > CoP > NiP。高H2/CO比有利于甲烷化反应进行,随着反应物H2/CO比的增加,所有磷化物催化剂的甲烷选择性都增加。Abstract: A series of metal phosphides including MoP, WP, CoP and NiP was prepared by temperature-programmed reduction with hydrogen from different phosphorus precursors. The effect of phosphorus precursor and feed H2/CO ratio on the catalytic performance of metal phosphides in the methanation was investigated. In comparison with diammonium hydrogen phosphate (DAP), phytic acid (PA) as a chelating agent can effectively disperse the metal precursor, reduce the reduction temperature, promote to form pure phosphide phase, and give the phosphide catalyst a higher surface area and a smaller particle size; as a result, the metal phosphides prepared with PA as a phosphorus precursor exhibit higher catalytic activity in methanation. In addition, the catalytic activity of various metal phosphides in methanation follows the sequence of MoP > WP > CoP > NiP. A high H2/CO ratio in the feed is favorable for the methanation over the phosphide catalysts; the selectivity to methane increases with an increase in the H2/CO ratio.
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Key words:
- phytic acid /
- methanation /
- phosphate /
- metal phosphide /
- H2/CO ratio /
- catalytic performance
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Table 1 Methanation performance of various metal phosphide catalysts at 550 °C, 3.0 MPa, and 5000 mL/(g·h)
Catalyst H2/CO = 1 H2/CO = 3 $x_{ {\rm{CO} } }$/% $ s_{{\rm{CO}}_2} $/% $ s_{{\rm{CH}}_4} $/% $ s_{{\rm{C}}_2{\rm{H}}_6} $/% $ x_{{\rm{CO}}} $/% $ s_{{\rm{CO}}_2} $/% $ s_{{\rm{CH}}_4} $/% $ s_{{\rm{C}}_2{\rm{H}}_6} $/% MoP-DAP 50.1 45.8 53.1 1.1 59.6 41.9 57.2 0.9 MoP-PA 65.6 46.8 51.9 1.3 72.5 31.9 67.5 0.6 WP-DAP 17.3 41.9 57.5 0.6 22.8 32.0 67.5 0.5 WP-PA 21.3 43.0 56.0 1.0 23.8 32.9 66.2 0.9 CoP-DAP 5.8 20.0 78.1 1.9 9.4 10.1 88.8 1.1 CoP-PA 12.4 23.6 75.8 0.4 17.3 16.8 82.1 1.1 NiP-DAP 3.2 13.4 84.0 2.6 3.4 7.0 90.3 2.7 NiP-PA 3.2 14.3 84.1 1.6 4.3 12.0 86.3 1.7 Table 2 Textural properties determined by N2 sorption of various phosphide catalysts
Catalyst Surface area A/(m2·g−1) Pore volume v/(cm3·g−1) Average pore size d/nm Particle size d/nm MoP-DAP 3.7 0.022 27.0 19.7 MoP-PA 40.1 0.010 8.9 14.7 WP-DAP 3.2 0.024 55.5 35.5 WP-PA 27.4 0.083 11.1 22.9 CoP-DAP 1.0 0.003 52.6 90.8 CoP-PA 10.9 0.062 30.2 38.1 NiP-DAP 4.0 0.029 48.1 25.8 NiP-PA 8.1 0.021 38.3 19.7 -
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