How can i write systematic data into excel sheet with systematicly?

I have been working with big though systematic data. Therefore I have wrote only shape of my data frame to below. I need to write every 3 column into different excel sheet. I tried some code and functions but i didnt achieve due to my lack of programming.

  x1 <- c(2,3,8,9)
  x2 <- c(4,6,2,1)
  x3 <- c(1,2,25,20)
  y1 <- c(45,15,56,74)
  y2 <- c(56,25,4,9)
  y3 <- c(92,52,4,9)
  z1 <- c(71,45,61,96)
  z2 <- c(31,4,78,7)
  z3 <- c(12,22,11,31)
  
  df<-data.frame(x1,x2,x3,y1,y2,y3,z1,z2,z3)
  
  df

  x1 x2 x3 y1 y2 y3 z1 z2 z3
1  2  4  1 45 56 92 71 31 12
2  3  6  2 15 25 52 45  4 22
3  8  2 25 56  4  4 61 78 11
4  9  1 20 74  9  9 96  7 31

Thanks for helps.

>Solution :

We could split by the names and then write to different files

lst1 <- split.default(df, sub("\\d+", "", names(df)))
library(openxlsx)
write.xlsx(lst1, file = "file.xlsx")