To extract a *.tar.xz file you need to install the xz-utils package and after that use the command unxz to extract the *.tar from *.tar.xz.

Install the xz-utils package

Copy the RPMs related to xz-utils and install them

[root@dbappweb rpm]# ll
-rw-r--r-- 1 root root 149504 Mar  5  2010 xz-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
-rw-r--r-- 1 root root  96793 Mar  5  2010 xz-libs-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
-rw-r--r-- 1 root root  15619 Mar  5  2010 xz-lzma-compat-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
[root@dbappweb rpm]# rpm -ivh xz-libs-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
warning: xz-libs-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing...                ########################################### [100%]
   1:xz-libs                ########################################### [100%]
[root@dbappweb rpm]# rpm -ivh xz-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
warning: xz-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing...                ########################################### [100%]
   1:xz                     ########################################### [100%]
[root@dbappweb rpm]# rpm -ivh xz-lzma-compat-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm
warning: xz-lzma-compat-4.999.9-0.3.beta.20091007git.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing...                ########################################### [100%]
   1:xz-lzma-compat         ########################################### [100%]

Extract or Decompress *.tar.xz File

Here I have to extract the *.tar.xz file given below

[root@dbappweb Wkhtmltopdf]# ll
-rw-r--r-- 1 root root 14541904 Jan 10 10:53 wkhtmltox-0.12.4_linux-generic-amd64.tar.xz

Use the command unxz or xz –decompress to extract *.tar.xz file to  *.tar

[root@dbappweb Wkhtmltopdf]# unxz wkhtmltox-0.12.4_linux-generic-amd64.tar.xz

OR

[root@dbappweb Wkhtmltopdf]# xz --decompress wkhtmltox-0.12.4_linux-generic-amd64.tar.xz

[root@dbappweb Wkhtmltopdf]# ll
-rw-r--r-- 1 root root 124702720 Jan 10 10:53 wkhtmltox-0.12.4_linux-generic-amd64.tar

Now use the command tar -xvf to extract the *.tar file

[root@tcpepsutil Wkhtmltopdf]# tar -xvf wkhtmltox-0.12.4_linux-generic-amd64.tar
wkhtmltox/
wkhtmltox/lib/
wkhtmltox/lib/libwkhtmltox.so.0.12.4
wkhtmltox/lib/libwkhtmltox.so.0
wkhtmltox/lib/libwkhtmltox.so.0.12
wkhtmltox/lib/libwkhtmltox.so
wkhtmltox/include/
wkhtmltox/include/wkhtmltox/
wkhtmltox/include/wkhtmltox/image.h
wkhtmltox/include/wkhtmltox/dllbegin.inc
wkhtmltox/include/wkhtmltox/pdf.h
wkhtmltox/include/wkhtmltox/dllend.inc
wkhtmltox/bin/
wkhtmltox/bin/wkhtmltoimage
wkhtmltox/bin/wkhtmltopdf
wkhtmltox/share/
wkhtmltox/share/man/
wkhtmltox/share/man/man1/
wkhtmltox/share/man/man1/wkhtmltopdf.1.gz
wkhtmltox/share/man/man1/wkhtmltoimage.1.gz
[root@tcpepsutil Wkhtmltopdf]# ll
total 122176
drwxrwxr-x 6 1000 1000 4096 Nov 22 2016 wkhtmltox

Note: I have performed the above steps on RHEL 5.8 64-bit server