No abstract

High temperature calcined spherical alumina material with macroporous structure is widely used in the typical strong exothermic industrial catalytic process due to its good heat transfer ability. Aiming at the problem that its low surface area limits the dispersion of active metals, an in situ growth method is applied to fabricate an alumina array on spherical alumina, while maintaining the heat transfer advantages. Taking the as-obtained modified alumina as support, a highly dispersed PdAg catalyst for selective hydrogenation of acetylene is synthesized, which exhibits a remarkable enhanced intrinsic activity. Moreover, when the conversion of acetylene reaches 90%, the selectivity toward ethylene still remains 89%. Preferred selectivity is assigned to more isolated Pd sites as well as high electronic density, which facilitates the desorption of the resulting ethylene. More importantly, the array modified catalyst exhibits good structural stability and resistance to carbon deposition. From one aspect, the decrease of the heat production rate over a single active site is conducive to reducing the reaction heat accumulation, thereby avoiding the formation of hot spots over the catalyst, which is a necessary condition for the endothermic reaction of carbon deposition. From another point of view, both the new generated outer opening pore structure and the original macroporous structure of the molded alumina are beneficial for the heat transfer.

Focusing on the simultaneous enhancement of activity and selectivity in α, β‐unsaturated aldehyde hydrogenation, we designed and prepared an ultrathin CoAl‐LDH supported Pt catalyst. A series of technologies revealed the ultrathin CoAl‐LDH support possesses the characteristic of dual defects, oxygen vacancy (VO) and cobalt vacancy (VCo). Then, two kinds of vacancy related interface sites were identified, namely Pt−VO−Coδ+ and Pt−VCo−OHδ−. Compared with the bulk catalyst, the ultrathin catalyst exhibits both enhanced intrinsic activity and C=O bond selectivity under the synergistic effect of the dual interface sites. Specifically, the Pt−VO−Coδ+ interface site changes the adsorption mode of cinnamaldehyde and promotes the activation of C=O bonds, thus leading to the improved cinnamyl alcohol selectivity. The H atoms of the Pt−VCo−OHδ− interface site participate in the hydrogenation process, which facilitates the mobility of active hydrogen and therefore promotes the intrinsic activity. More importantly, the ultrathin catalyst shows good reusability.

Cinnamaldehyde (CAL) is a typical sustainable biomass molecule which is classified as α, β-unsaturated aldehydes. Selective hydrogenation of CAL to produce high-value and fine chemical cinnamylalcohol (COL) is an attractive catalytic transformation process. However, the hydrogenation of C=O bond in CAL is more unfavorable than C=C bond in thermodynamics and kinetics, leading to great challenge on achieving high yield of unsaturated alcohol. In this work, a Pt/CoAl-LDHs catalyst was prepared for hydrogenation of CAL to COL, showing outstanding intrinsic activity (TOF as high as 4.93 s À 1 ) and finally achieving 93.6 % selectivity at 95.4 % conversion. In contrast, the yields of COL over Pt/Co(OH) 2 and Pt/Al(OH) 3 were only 73 % and 34 % respectively. Characterizations including Raman, O-XAFS, XPS revealed that the Co 2 + À O 2À À Al 3 + structure in CoAl-LDHs contributed to strengthened metal-support interactions, and resulted in electron-rich and geometric decoration Pt δÀ sites. The electron-rich Pt δÀ provided preferable H 2 activation capability, and also exposed abundant unsaturated sites which optimized the adsorption mode of cinnamaldehyde favorable for C=O hydrogenation. However, in Pt/Co(OH) 2 and Pt/Al(OH) 3 catalysts, the Pt 0 without electron-rich and unsaturated property cannot improve the H 2 activation capability as well as electronic repellency to C=C bond. In addition, a possible catalytic mechanism was proposed to illustrate the role of Pt δÀ À Co 2 + À O 2À À Al 3 + interfacial structure on enhancing activity and selectivity.

Aiming at the low surface area of high-temperature-calculated alumina limits the dispersion of active metals, an in-situ growth method is applied to fabricate the alumina array modified spherical alumina. Taking the modified alumina as support, the highly dispersed PdAg catalyst for selective acetylene hydrogenation is synthesized, which exhibits a remarkable enhanced intrinsic activity. Moreover, when the acetylene conversion reached 90%, the ethylene selectivity remains 89%. Preferred selectivity is assigned to more isolated Pd sites and high electronic density, which facilitates the desorption of the resulting ethylene. More importantly, the modified catalyst exhibits good structural stability and resistance to carbon deposition. From one aspect, the decrease of heat production rate over active site is conducive to reduce the reaction heat accumulation, thereby avoiding the formation of hot-spots over the catalyst. From another point of view, the outer opening pore structure of the modified alumina are benefit for the heat transfer.