摘要
用XRD,N2吸附,NH3TPD和Py IR等手段对REHY分子筛进行了表征,并通过多晶XRD法测定了稀土离子在Y分子筛骨架外的分布.结果表明,在含水条件下,定位于Y型分子筛β笼SⅠ′位的RE3+与骨架氧及定位于SⅡ′位的H2O配位,稳定了分子筛的骨架,减少了分子筛酸性中的最强酸部分;定位的RE3+通过极化定位的配位水,增加了分子筛的中强酸,减缓了RE3+取代H+所引起的酸量下降.从结构测定可推测出,在FCC催化剂中Y型分子筛上RE3+的最佳量应为每个晶胞含11个稀土离子,并完全定位于β笼的SⅠ′位.
In the fluid catalytic cracking (FCC) process, REHY is the main active component of cracking catalyst for reducing naphtha olefins. The loading, position, occupation and coordination of RE3+ on HY zeollte directly affect not only the acid amount (density of acid centers), acidic intensity and the ratio of Bronsted acid to Lewis acid, but also the catalytic activity of the FCC catalyst. In an effort to understand the effect of RE3+ distribution and positions in Y zeolite on the acidity of the catalyst, the REHY zeolite was characterized by XRD, N-2, adsorption, NH3 -TPD and Py-IR. The distribution of RE3+ outside the framework of the Y zeolite was det ermined by polycrystalline XRD with the Rietveld method. RE3+ replaced Na+ or H+ in the Y zeolite and situated at S-I(') sites in β cages. As a result, they made the framework of Y zeolite more stable and improved the hydrothermal stability. Besides they were coordinated with the framework oxygen of Y zeolite, they were also coordinated with the water situated at S-II(') sites. This behavior reduced the strongest acid sites of the Y zeolite. When RE3+ situated at S sites polarized water situated at S-II(') sites, the mild strong acid sites of the Y zeolite were increased, and the reduction of acid sites in the Y zeolite was slowdown. The determination of the REHY structure showed that 11 RE3+ in every cell of the Y zeolite in FCC catalyst should be the optimum value, and they all should be situated at S sites in P cages. If there was much more RE3+ in the catalyst, the number of H+ lons polarized by RE3+ on an average reduced. In addition, some of them would enter into the supercages and reduce the total acid amount on a large scale.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2005年第4期301-306,共6页
基金
国家自然科学基金资助项目(2037302).
