To study the effect of SiO2 on the physicochemical characteristic of modified biochar, bio-chars were obtained at 600℃in a vertical furnace from a pyrolysis of rice straw, cotton stalk, and rice husk. Bio-chars were activated at different temperatures (400, 600, 800, and 1 000℃) in a gaseous NH3 and/or CO2 atmosphere. The variation of chemical properties, the CO2 adsorption capacities, and the physicochemical properties linked with an ash analysis of different raw chars and modified chars were investigated. An X-ray fluorescence (EARGE Ⅲ, EDAX Inc.) and an ion chromatograph (ICS-90, Dionex) were used according to the national standard of GB/T1574 to analyze the ash composition of pyrolytic biochars. The content of SiO2 in rice husk char (87.47%) was the highest among the studied samples, followed by rice straw and cotton stalk chars, which were 51.99%and 18.21%, respectively. However, according to the proximate analysis of biomass raw materials, the proportion of ash in rice straw and rice husk was about 2-3 times of that of cotton stalk, therefore, the amount of SiO2 retained in rice husk and rice straw was nearly 15 times and 4-5 times of that in cotton stalk, respectively. The production and modification of biomass chars were carried out in a self-designed vertical furnace reaction system which included two parts: A gas generating zone and a modification reaction zone. The modification reaction zone mainly consisted of a stainless steel reactor (inner diameter 38 mm, outer diameter 40mm, and height 600 mm) and a temperature programmed furnace.A Fourier transform infrared spectrum analyzer (VERTEX70, Bruker) was used to analyze the variation of chemical properties and surface functional groups of biochars before and after NH3 modification at different temperatures. And the Fourier transform infrared spectra of the corresponding biomass raw materials linked with a proximate and ultimate analysis were also presented to compare with that of chars and modified chars. The results showed that in the NH3 atmosphere, a certain amount of nitrogen had been introduced onto the surface of chars, but the amount of N-containing functional groups that was introduced into rice straw chars or rice husk chars were obviously lower than that of cotton stalk chars which may be caused by the large amount of SiO2 that remained in the ash of rice straw and rice husk. The bond energy of Si-O was considerable high, which usually cracks above 1 400℃ and is very difficult to react with the free radical groups such like –NH2 and –NH under an NH3 atmosphere. Since there is a large amount of Si-O function group on the surface of rice straw or rice husk chars, it will hinder the reactions between –NH2, -NH and other radical groups and chars, which will reduce the total modification efficiency of pyrolytic chars. The CO2 adsorption capacities of biochars before and after modification were investigated by an automatic adsorption instrument (ASAP2020, Micromeritics) at room temperature. Experimental results showed that the positive influence of CO2 on pore structure evolution and the introduction of N-containing function groups into char structure may be weakened by SiO2. Bio-chars derived from cotton stalk which were modified under a CO2 atmosphere showed the best CO2 adsorption capacities among all the modification methods and different feedstock. It indicated that modified bio-chars with lower SiO2 content showed better CO2 adsorption performance.%为了探索SiO2对改性生物质焦理化特性的影响，以稻秆、棉秆、稻壳作为原料，在600℃下热解制备生物质焦；焦样再经不同温度下NH3/CO2高温气态改性后获得对CO2具有高选择性的富氮生物质焦。采用傅立叶红外光谱分析改性前后生物质焦的表面官能团结构，利用ASAP2020自动吸附仪测量其常温变压下的CO2吸附量，并结合 X 射线荧光光谱对热解焦的灰成分进行分析，探讨不同原料的生物质焦改性过程中，其理化特性的演变。研究表明，生物质焦灰分中过高的SiO2会阻碍其高温下CO2的活化作用及NH3的氨化作用；焦样灰分中的SiO2含量越低，其改性效果越理想。
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