$patterns[0] = '/ adsense /';
$patterns[1] = '/ google /';
$patterns[2] = '/ ppc /';
$replacements[2] = " <a href=\"http://google.com/adsense\">Adsense</a> ";
$replacements[1] = " <a href=\"http://google.com\">Google</a> ";
$replacements[0] = " <a href=\"http://google.com/adwords\">PPC</a> ";
$content = preg_replace($patterns, $replacements, mb_strtolower($content, mb_detect_encoding($content)));