四甲基氢氧化铵辅助合成SSZ-13分子筛及其甲醇制烯烃的催化性能

Synthesis of SSZ-13 Molecular Sieve Using Tetramethylammonium Hydroxide as an Auxiliary and Its Catalytic Performance in Methanol to Olefins Reaction

以N,N,N-三甲基金刚烷氢氧化铵(TMAdaOH)为模板剂合成SSZ-13分子筛,探讨有机季铵碱四甲基氢氧化铵(TMAOH)取代体系中的氢氧化钠(NaOH)对SSZ-13分子筛合成的影响,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅里叶红外光谱(FT-IR)、热重-微商热重(TG-DTG)、NH_3程序升温脱附(NH_3-TPD)和N_2吸附-脱附等手段对合成样品进行表征,分析合成凝胶的硅/铝比对SSZ-13分子筛的结晶度、比表面积、酸量等的影响,并考察了SSZ-13分子筛在甲醇制烯烃(MTO)反应中的催化性能。结果表明,当有机碱TMAOH完全取代NaOH时,合成样品的结晶度从92.68%提高至108.75%,且合成体系的硅/铝比(n(SiO_2)/n(Al_2O_3))范围可以显著拓宽(33～100),合成产物的硅/铝比也相应提高,比表面积可增大至约800 m^2/g,强酸量减少,SSZ-13分子筛样品在MTO催化反应中表现出了更长的寿命和更高的双烯(乙烯+丙烯)选择性。

Effects of the replacement of NaOH by tetramethylammonium hydroxide (TMAOH) on the synthesis of SSZ-13 molecular sieve were investigated in the presence of the N ,N ,N -trimethyl-1-adamantanammonium hydroxide (TMAdaOH) as structure-directing agent.The influences of silica/alumina ratios in synthetic gel on the structural,textural and acidic properties of SSZ-13 molecular sieve were investigated.The obtained SSZ-13 molecular sieves were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),Fourier transform infrared (FT-IR),thermogravimetry-derivative thermogravimetry (TG-DTG),NH 3-temperature programmed desorption (NH 3-TPD) and N 2 physisorption techniques.The catalytic performance of the SSZ-13 molecular sieves was evaluated by methanol to olefins (MTO) reaction.Results demonstrate that the crystallinity of the product significantly increases from 92.68% to 108.75% when the organic alkali TMAOH completely take place of the inorganic NaOH.The silica/alumina ratio in synthesis gel ranges from 33 to 100,thus accordingly enhancing the silica/alumina ratio of molecular sieves.Meanwhile,these materials possess large BET surface area of 800 m 2/g and low strong acid amount,therefore exhibit longer catalytic lifetime and higher light olefin (ethylene + propylene) selectivity than conventional SSZ-13 catalysts in MTO reaction.