**Waste Seashells as a Highly Active Catalyst for Cyclopentanone Self-Aldol Condensation**

**Xueru Sheng 1,**†**, Qianqian Xu 1,**†**, Xing Wang 1, Na Li 1, Haiyuan Jia 2, Haiqiang Shi 1, Meihong Niu 1, Jian Zhang 1,\* and Qingwei Ping 1,\***


Received: 29 July 2019; Accepted: 31 July 2019; Published: 1 August 2019

**Abstract:** For the first time, waste-seashell-derived CaO catalysts were used as high-performance solid base catalysts for cyclopentanone self-condensation, which is an important reaction in bio-jet fuel or perfume precursor synthesis. Among the investigated seashell-derived catalysts, *Scapharca Broughtonii*-derived CaO catalyst (S-shell-750) exhibited the highest dimer yield (92.1%), which was comparable with commercial CaO (88.2%). The activity sequence of different catalysts was consistent with the CaO purity sequence and contact angle sequence. X-ray diffraction (XRD) results showed that CaCO3 in waste shell were completely converted to CaO after calcination at 750 ◦C or above for 4 h. CO2 temperature-programmed desorption (CO2-TPD) results indicate that both the amount and strength of base sites increase significantly when the calcination temperature climbs to 750 ◦C. Therefore, we can attribute the excellent performance of S-shell-750/850/950 catalysts to the higher CaO content, relatively low hydrophilicity, and stronger acidity and basicity of this catalyst. This study developed a new route for waste shell utilization in bio-derived ketone aldol condensation.

**Keywords:** biomass; waste seashell; aldol condensation; heterogeneous catalyst
