there are some abstracts of some papersextract the information of number of the paper,type of the paper(review or experimental research),single_atom_material(related atom and/or material fucused on),aimed_issue(the aimed issue/challenge/difficulty),application,breakthrough(key breakthrough/conclusion/result/meaning).reply using json format,and strictly in:{number:{type:info,single_atom_material:info,aimed_issue:info,application:info,breakthrough:info}},info means exacted information,and if info is not found,which strictly use:null:
[number 5] Single-atom catalysts (SACs) show expressively enhanced activity toward diverse reactions due to maximized atomic utilization of metal sites, while their facile, universal, and massive preparation remains a pronounced challenge. Here we report a facile strategy for the preparation of SACs by use of the inherent confined space between the template and silica walls in template-occupied mesoporous silica SBA-15 (TOS). Different transition metal precursors can be introduced into the confined space readily by grinding, and during succeeding calcination single atoms are constructed in the form of M-O-Si (M = Cu, Co, Ni, and Zn). In addition to the generality, the present strategy is easy to scale up and can allow the synthesis of 10 g of SACs in one pot through ball milling. The Cu SAC has been applied for CO cycloaddition of epichlorohydrin, and the activity is obviously higher than the counterpart prepared without confined space and various reported Cu-containing catalysts.
 Provide your response in exactly 6 paragraphs (separated nearby paragraphs with 3 aterisk symbols ***).
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