Novel polyhedral@SiO₂ core–shell catalysts designed for Fischer–Tropsch synthesis

Abstract

Background: Fischer-Tropsch synthesis (FTS) has attracted much attention for converting syngas to liquid fuels. Enhanced catalytic stability and excellent product selectivity can be achieved by rational design of catalysts. However, the traditional SiO 2 -supported Fe-based catalysts display higher interaction between active metal and SiO 2 support, thus resulting in a lower catalytic activity. Rational design of catalysts with weaker Fe-Si interaction promises excellent catalytic performances.Results: Novel polyhedral@SiO 2 core-shell catalysts with adjustable shell thickness were prepared. The incorporation of SiO 2 shell with suitable thickness can maintain the integrity of the active structure, and thus promising excellent C 5+ productivity combined with higher catalytic activity. On the other hand, the SiO 2 layer can prolong the residence time of C n H m intermediates on the active surface of Fe particles that enhance the C-C coupling reaction, favoring chain growth for production of C 5+ yield. However, excessive addition of tetraethyl orthosilicate cannot increase the shell thickness in the absence of ammonium hydroxide and can be responsible for a poor CO conversion. Si-66 with shell thickness of 66 nm achieves an optimum C 5+ yield of 2.23 × 10 −3 g HC g Fe −1 s −1 and a higher iron time yield value of 31.5 ∼mol CO g Fe −1 s −1 . Obviously, this C 5+ yield is comparable to that for the Mn-promoted FeSiMn catalyst (2.22 × 10 −3 g HC g Fe −1 s −1 ) reported in our previous work.Conclusions: The introduction of SiO 2 as shell can improve structural stability during FTS. Moreover, the novel polyhedral@SiO 2 core-shell catalyst exhibits excellent C 5+ yield, and which is 1.8 times higher than that for a spindle@SiO 2 core-shell catalyst reported in our previous work.